FORENSIC DNA ANALYSIS:
TECHNOLOGY AND APPLICATION
Science and Technology Division
DNA AND MOLECULAR GENETICS
Variable Number Tandem Repeats (VNTR)
Restriction Fragment Length Polymorphisms (RFLP)
Short Tandem Repeats (STR)
Polymerase Chain Reaction
Mitochondrial DNA (mDNA)
OF FORENSIC-DNA PROFILING
RFLP (Restriction Fragment Length Polymorphism) Analysis
PCR/STR (Polymerase Chain Reaction/Short Tandem Repeat) Analysis
DNA DATA BANKS
Use of DNA Data Banks in Other Countries
A Proposed Canadian DNA Bank
Canadian Bar Association
Canadian Police Association
TECHNOLOGY AND APPLICATION
It will be long before
a British jury will consent to convict a man upon the evidence of his
finger prints; and however perfect in theory the identification may
be, it will not be easy to submit it in a form that will amount to a
- From an 1892 review in The Athenaeum
of Finger Prints, by Sir Francis Galton.(1)
The proposal that human
fingerprints could be used as a tool for identification, and as evidence
in criminal proceedings, was revolutionary in its day. Francis Galtons
century-old caution notwithstanding, however, the use of fingerprints
as evidence has been long established as an invaluable tool in the prosecution
of criminals, as well as in the identification of missing persons and
Over the past decade, a
forensic technology even more revolutionary in concept than fingerprints
has entered into common use. Forensic-DNA typing, or profiling, was first
used in 1986 in England in the case of Colin Pitchfork, who was eventually
convicted of the sexual assault and murder of two teenage girls. It is
significant to note, in light of recent developments in Canada, that the
technology was used in this initial case to exonerate a young man who
had falsely confessed to the murders.
In an attempt to identify
the murderer of the teenage girls in the Pitchfork case, the police authorities
took the extraordinary step of requesting the entire male population of
the area to give DNA samples voluntarily for testing. Colin Pitchfork
at first avoided being tested by the new technique by persuading an acquaintance
to give a blood sample on his behalf. Later, after Pitchfork had been
arrested for the murders (without the involvement of forensic-DNA profiling),
the DNA-typing procedure proved that he had, indeed, committed both crimes.
He is now in prison serving a number of concurrent sentences, including
two life sentences for murder.(2)
The value of forensic-DNA
profiling in exonerating innocent persons has recently been much in the
news in Canada, in connection with two murder cases. In 1985, Guy Paul
Morin was arrested for the murder of nine-year old Christine Jessop, a
crime that also involved sexual assault. Morin was acquitted in his first
trial (in 1986) but was re-tried, and convicted, in 1992. In 1995, after
15 months in prison, Morin was exonerated on the basis of DNA testing,
a technology not available when the crime had originally been committed.
In fact, the DNA sample obtained from Christine Jessops clothing
was so degraded by 1995 that an advanced form of the technology, only
recently perfected, was needed to perform the analysis. The Morin case,
and the manner in which it was originally investigated and prosecuted,
is currently under intense review by the Ontario government.
More recently, forensic-DNA
analysis was used to exonerate David Milgaard, who had been convicted
in 1969 of the rape and murder of Gail Miller in Saskatoon. Milgaard spent
almost 23 years in prison.(3)
The Milgaard case differs from the Morin case in several important ways.
First, there was a large amount of DNA (from semen) available for analysis
from the clothing of Gail Miller. A U.S. forensic serologist, Edward Blake,
who is also an expert on forensic-DNA, has suggested that this material,
properly analyzed, would almost certainly have exonerated Milgaard in
1992 when new tests were carried out.(4)
The second major way in
which the Milgaard case differs from that of Guy Paul Morin is that police
have since arrested a suspect on the basis of the forensic-DNA evidence
developed in 1997. Larry Fisher, a convicted serial rapist, who had long
been suspected of being involved in the rape and murder of Gail Miller,
has been arrested by the RCMP; Fishers DNA profile matches that
obtained from the semen taken from Gail Millers clothing.(5)
Forensic-DNA profiling has
now been used in many criminal and civil cases around the world, and has
become an established technology. The first time DNA-typing evidence was
used in Canada was in 1988. By October 1989, the central RCMP laboratory
in Ottawa was able "to offer a national casework service in forensic
DNA typing."(6) In addition
to the Morin and Milgaard/Fisher cases described above, one of the most
notorious cases in which the prosecution has used DNA-typing evidence
in this country was the 1991 murder trial of Allan Legere in New Brunswick.
Legere was eventually found guilty of murder, partly on the basis of the
In this paper, the technology
of forensic-DNA analysis and profiling will be described and the idea
of establishing a national forensic-DNA data bank will be discussed. First,
however, is a short summary of the scientific background that has led
to the development of the DNA-profiling procedure.
DNA AND MOLECULAR GENETICS
All living organisms are
composed of cells, the basic integrated units of biological activity.
In humans, as in other higher organisms, the hereditary material deoxyribonucleic
acid, or DNA, is contained in the cell nucleus in microscopic
assemblages known as chromosomes. Human cells have 23 pairs of
chromosomes for a total of 46. A typical human cell has one pair of sex
chromosomes, and 22 pairs of non-sex chromosomes, known as autosomes.
The units of inheritance are known as genes: human beings are thought
to have 50,000 - 100,000 genes which are contained in the chromosomal
DNA in the cell nucleus.
The history of forensic-DNA
analysis, also called forensic-DNA typing, (or popularly, "DNA fingerprinting"),
is little more than a decade old. The basic science goes back at least
to 1953, however, when two young Cambridge University researchers, James
Watson and Francis Crick, discovered the molecular structure of DNA.(7)
Their landmark paper in molecular genetics opened the way for the dramatic
advances in recent years in our understanding of inheritance, development
and metabolism. Any discussion of DNA typing and its important contribution
to forensic science therefore requires some understanding of the molecular
basis of inheritance.
DNA is a complex double-chained
molecule twisted into a helical form: the "double helix" structure
that has become familiar through popular science articles. The structure
of DNA resembles a spiral ladder in which the "sides" are made
of sugar-phosphate molecules and the "rungs" are formed from
pairs of chemicals known as bases or nucleotides. In DNA
from all sources there are only four bases: adenine, thymine, guanine
and cytosine. The pairing of the bases is specific: adenine is always
paired with thymine, and cytosine is always paired with guanine. In biochemical
shorthand, as shown in Figure 1, the base-pairs are represented as A-T
(adenine-thymine) and G-C (guanine-cytosine). It is estimated that there
are about 3 billion base-pairs in the human genome, the term
used to describe the total hereditary material in the 46 chromosomes.
These four nucleotide bases
represent the "genetic alphabet" and the sequences of base-pairs
along the length of the DNA molecule comprise a biochemical vocabulary
which encodes the genetic information essential to life processes. The
absolute specificity of base-pairing also provides a mechanism through
which "parent" DNA molecules can be copied to form identical
"daughter" DNA molecules in the process of reproduction. The
mechanism, known as replication (as opposed to duplication), is
possible because the two sides of the parent DNA molecule are complementary
rather than identical. In the replication process, the parent DNA molecule
"splits" along its length, each side serving as a template
for one of the new (and identical) daughter molecules.
Although genes are composed
of DNA and contained in the chromosomes in the nucleus of the cell, only
a small fraction of that DNA is actually used to form genes. Put another
way, most of the DNA in our chromosomes has no known function; the portion
of such DNA may be more than 95% of the total complement in humans.(8)
Another source suggests that only 2.5-3.3% of DNA can be expected to be
found in the genes.(9)
These observations seem
to fly in the face of traditional (or evolutionary) logic which dictates
that any cellular component, particularly one as important as DNA, must
have an essential function. The presence of so much DNA with no known
genetic role in chromosomes is a mystery. Ironically, however, it is this
chromosomal "flotsam and jetsam" or "junk DNA" that
is of special interest to the forensic scientist.
In the next several paragraphs,
a number of terms essential to an understanding of forensic DNA analysis
will be introduced and discussed.
Variable Number Tandem Repeats (VNTR)
The specific base-pair sequences
in the genes are known to define the function a certain gene will perform
in the organism. It is also known that the non-coding DNA contains repeated
base-pair sequences arranged in tandem which, while having no known function,
are inherited by the individual from his/her parents just as functional
genes are inherited. (Coding DNA also contains such repeats, but less
commonly than non-coding DNA.) These tandem repeats, in total,
make up a molecular-DNA "fingerprint" that is believed to be
unique for each individual (with the possible exception of identical twins)
because the number of repeated sequences can vary from person to person.
These non-coding base-pair repeated sequences bear the complicated name
variable number tandem repeats, abbreviated to VNTR.
When DNA is extracted for
use in forensic analysis, the DNA is cut into fragments by enzymes,
special chemicals which break down large molecules (such as DNA) into
smaller sub-units. An enzyme which is used to cut the DNA molecule into
fragments is called a restriction enzyme, restriction nuclease,
or restriction endonuclease, the first and last being abbreviated
to RE. Many different REs are known and they are differentiated
on the basis of the point at which they will cut the DNA molecule. That
point is known as a recognition sequence, a specific sequence of
four, five or six nucleotides.
The resulting fragments
of DNA produced by the enzyme's action will differ in length from person
to person. There are two reasons for this. One reason is that the cutting
sites of different individuals DNA may appear at different places
along the molecule. The second reason is that the region of DNA between
cutting sites may contain more or fewer tandem repeats of nucleotide sequences,
hence the name "variable number tandem repeats."
Restriction Fragment Length Polymorphisms (RFLP)
The DNA fragments of interest
in forensic-DNA analysis and typing are called restriction fragment
length polymorphisms, abbreviated to RFLP (pronounced "riflip").
The term "polymorphism" refers to the fact that genes, and non-coding
DNA sequences, can exist in more than one form on separate chromosomes.
The reader will recall that chromosomes exist in pairs, one pair inherited
from each parent. Where a specific gene, or non-coding DNA sequence, is
identical on each of the pair of chromosomes, the condition is said to
be homozygous, in contrast to a heterozygous condition,
where the two genes, or sequences, differ in some way.(10)
The physical basis of the
differences lies in the nucleotide sequences in the DNA molecule. The
sequences will differ in one or more nucleotide pairs, which is an actual
physical difference; hence the term "polymorphism," which means,
literally, more than one form. RFLPs occur both in the coding regions
of DNA (that portion of the DNA which codes for genes), and in non-coding
DNA, which does not have a genetic function. RFLPs are quite common in
the human genome, and at least several thousand have been identified.
RFLPs have been extremely useful in the diagnosis of genetic disease;
for example, the malfunctioning gene that causes cystic fibrosis was located
precisely on human chromosome 7 through the use of a series of RFLP markers.(11)
The methods by which RFLPs
are detected, identified and utilized in forensic-DNA typing, are described
in the next section.
Short Tandem Repeats (STR)
Short tandem repeats, as
the name implies, are similar to VNTRs described above, except that the
repeated units are much shorter. Those fragments chosen for forensic use
generally have a tandem repeat unit of only three to four base-pairs,
which may be repeated in the DNA molecule from a few to dozens of times.
Clearly, units of only three to four base pairs are extremely small; this
presents both an advantage and a problem in forensic-DNA work. The advantage
is that only small amounts of even badly degraded DNA may be sufficient
for forensic use. The problem is that a very small sample of very short
DNA segments - the short tandem repeats - needs to be increased in size
for analytical convenience and efficiency. This is done through the use
of a relatively new technology known as the polymerase chain reaction.
Polymerase Chain Reaction
The polymerase chain reaction,
or PCR, is an innovative technique for increasing the amount of
a specific sequence of DNA in a sample. The technique has proven to be
invaluable in forensic-DNA work, and is also used widely in genetic research
The term "polymer"
- which literally means "many parts"- refers to a chemical molecule
made of a very large number of repeated units of one or more small molecules.
A "polymerase" is an enzyme that produces multiple copies of
(in the context of this discussion) a specific segment of DNA; the "chain
reaction" aspect means that the process will continue for as long
as desired to produce the required amount of DNA. Literally, PCR can make
millions or billions of copies of a selected, or target, DNA sequence,
in a test tube, and accomplish this feat within a matter of a few hours.(12)
This is technically called "DNA amplification"; in popular parlance,
it is sometimes referred to as "molecular Xeroxing."
The PCR process is similar
to the mechanism by which DNA duplicates itself in the cell. There are
three steps in the process, as carried out in the laboratory: first, the
double-stranded DNA segment, or sequence, is separated into two strands
by heating; next, the single-stranded segments are prepared through being
hybridized with "primers" - short DNA segments - that define
the target sequence to be amplified; and, third, the enzyme DNA polymerase
is added to the mixture, along with a quantity of the four nucleotide
bases, and the replication process begins.(13)
The three-step cycle is repeated, usually 25-30 times.
Dr. Ron Fourney, who is
with the RCMPs Central Forensic Laboratory in Ottawa, is a recognized
expert on forensic-DNA typing, particularly in the use of PCR:
The PCR method uses basic
cellular chemistry and enzymes in a controlled "molecular copying
process" to synthesize (amplify) exponential numbers of "target
sequence" from the original DNA extracted from forensic samples.
PCR technologies selectively amplify DNA fragments of interest to the
forensic scientist and capitalize on fragments that have common differences
As noted, the PCR technology
is particularly useful where forensic-DNA typing is carried out using
short tandem repeats (STR). This technology will be discussed below.
Mitochondrial DNA (mDNA)
Not all of the DNA in human
and other organisms is located in the chromosomes in the nucleus of the
cell. Some DNA is found in organelles called mitochondria, which
are within the cells but outside the nucleus of the cell. The mitochondria
carry out essential metabolic functions, notably with respect to cellular
energy production and respiration. Although mitochondrial DNA is not often
used for forensic purposes, it can be - and has been - used in certain
situations to establish family relationships.
The most celebrated use
of such DNA for identification purposes took place in September of 1992
when scientists with the Forensic Science Service in the United Kingdom
were asked to analyze mDNA from the bones of five bodies exhumed from
a grave in Ekaterinburg in the Ural Mountains in Russia. Ekaterinburg
is the location where Czar Nicholas II and his family were murdered in
Mitochondrial DNA is passed
from one generation to the next, essentially unchanged, solely through
the maternal line of a family. (Unlike the eggs from the female, the male
sperm does not typically contribute mitochondria to the offspring.) By
comparing the mitochondrial DNA from the five exhumed bodies with that
from a blood sample donated by Prince Philip (whose maternal grandmother
was Czarina Alexandra's sister), and also with that in blood from two
surviving maternal relatives of the Czar, scientists were able to demonstrate,
with approximately 99% certainty, that the bodies found in Ekaterinburg
were in fact those of the Russian Royal Family.(15)
Using the same technology,
scientists have also been able to demonstrate that Anna Anderson, who
claimed to be the Princess Anastasia, was a fraud.(16)
OF FORENSIC-DNA PROFILING
The current level of sophistication
and expertise in the science and technology of molecular genetics has
provided the basis for the "genome project," an international
program to determine the sequence of all the base-pairs in the 23 pairs
of human chromosomes. The approximately 3 billion base-pairs in the human
genome incorporate both the specific sequences which constitute functional
genes, and the 95% (or more) of human DNA which is non-coding; that is,
which has no known genetic function. It is important to understand that
the genome project is separate, and different, from forensic-DNA profiling,
although some of the same technologies are used in both activities.
Another essential point
is that the DNA profile, or "DNA fingerprint," of an individual
as used in forensic-DNA profiling does not represent the genetic make-up
of that person. It represents only a number of fragments of the person's
DNA; these have been extracted, processed and utilized to form an individualized
molecular-DNA "snapshot" that can be used for identification
purposes. The forensic-DNA profile does not give any information on the
individuals genetic make-up.
Forensic-DNA profiling can
make use of any specimen that contains DNA. As shown in Figure 2, the
list can include hair (with the root attached), blood stains, semen, bone
marrow, or any other tissue or bodily fluid that has nucleated cells.
In the use of blood stains, it is the DNA from the white blood cells that
is used: mature human red blood cells do not have nuclei and so contain
no DNA. Semen normally contains large amounts of DNA in the sperm cells,
which makes it very useful for DNA typing, especially in cases of sexual
assault. (If the rapist had been vasectomized, however, there would be
no sperm cells and the specimen would not be useful with current RFLP
The standard forensic-DNA
typing technology initially used in Canada was the RFLP technology; this
is now being replaced by the newer PCR/STR (polymerase chain reaction/short
tandem repeat) technology. As of May 1997, the RCMPs Central Forensic
Laboratory in Ottawa, as well as the laboratories in Regina and Vancouver,
had converted to PCR/STR from RFLP; the RCMP laboratories in Halifax and
Edmonton were still using the RFLP technology; and the Winnipeg laboratory
was using both technologies. Full conversion of the RCMP forensic laboratory
system to PCR/STR analysis is expected to be completed in early 1998.(17)
The Centre for Forensic Sciences in Toronto also uses the PCR/STR technology.
RFLP (Restriction Fragment Length Polymorphism) Analysis
The following description
of RFLP analysis is illustrated in Figure 3.
First, the DNA is extracted
from the specimens, using established procedures. In the next step, the
extracted DNA is broken into fragments, using restriction enzymes. Although
there are several hundred such enzymes, or REs, available today, the laboratories
of most North American law enforcement agencies and governments (Canada
included) selected one specific RE (called "HaeIII")
in order to achieve uniform results and to facilitate "networking"
of DNA-typing information.
After the extracted DNA
has been digested by the enzyme, the various fragments are sorted according
to size, using a technique called agarose gel electrophoresis,
initially used in genetics research and adapted to forensic use. Agarose
gel is a jelly-like material containing pores through which the DNA molecules
can pass. The digested DNA samples are loaded into slots at one end of
a flat slab of the gel. An electric current is applied across the gel
causing the DNA fragments to migrate through the material. The smaller
fragments migrate farther than the larger ones, to give the end result
of an orderly array of fragments separated by size.
In the next step, the DNA
fragments are denatured by soaking the gel in an alkali solution.
In denaturing, the hydrogen bonds holding the two sides of the double
helix of the DNA together are broken, with the result that there are now
single-stranded DNA fragments arrayed on the gel in place of the
original double-stranded fragments.
Because the agarose gel
is not sufficiently stable to be used in the rest of the RFLP-typing procedure,
the DNA fragments are transferred to the surface of a thin nylon membrane.
This technique, called "Southern blotting" or "Southern
transfer," is named for Edwin Southern, the scientist who developed
it. When the DNA is fixed to the nylon membrane, the fragments are ready
to be analyzed.
The subsequent analytical
technique is called nucleic acid hybridization.
The term is explained as follows. Hybridization is a process that involves
pairing the single-stranded DNA (nucleic acid) fragments on the nylon
membrane with specific complementary DNA strands; the reader will recall
from the earlier discussion that the double-stranded DNA molecule comprises
two complementary, rather than identical, strands.
The hybridization is carried
out with strands of DNA which have been labelled with a radioactive isotope,
usually an isotope of phosphorus. These strands are known as DNA probes,
so-called because their base sequences are known and they are used specifically
to bind only to those DNA strands containing complementary sequences.
Because the probes carry a radioactive label, the newly hybridized strands
can be visualized as images on an x-ray film. The visual result is often
compared to a supermarket "bar code."
The specimen in question
can then be compared with known specimens through their x-ray images.
If there is a difference in the patterns between the DNA from the suspect
individual and the DNA from the specimen taken from the crime scene, the
suspect will be exonerated. If the patterns match, the prosecution can
use this fact as evidence linking the suspect to the crime scene.
PCR/STR (Polymerase Chain Reaction/Short Tandem Repeat) Analysis
As noted above, the RFLP
technology is being replaced in Canada by the newer PCR/STR technology.
In some basic respects,
PCR/STR technology is similar to the RFLP technology described above.
The selection and extraction of the DNA is the same, and in both technologies
the selected fragments of DNA are placed in a special gel and sorted by
size through the use of an electric current. However, with PCR/STR, a
much smaller amount of DNA in a sample is adequate to carry out the profiling;
even badly degraded DNA, such as might be obtained from decayed or severely
burned bodies, can be used. In fact, enough DNA can be extracted from
a single hair follicle, or from a saliva trace on a cigarette butt or
envelope, to carry out the profiling using this technology.(18)
Additional advantages of PCR/STR are that the technology is less susceptible
than earlier PCR-based methods to being compromised by contaminants, and
there is a "significant advantage in deciphering the origin of specific
DNA profiles from complex sample mixtures...i.e., mixed blood stains,
commingled remains and sexual assault samples."(19)
The principal difference
between the two technologies is the use of polymerase chain reaction (PCR)
to amplify the amount of DNA in the sample. A second important difference
is that the PCR/STR technology lends itself well to the use of fluorescent
labels for detecting the DNA bands visually, and several such systems
have been developed. Also, fluorescence is amenable to automated detection,
which greatly facilitates subsequent analysis of the forensic-DNA profiles
and the storage and retrieval of data.(20)
Dr. Fourney describes the
use of automated fluorescent detection, as follows:
A major tool employed
by both clinical diagnostic laboratories and numerous larger forensic
laboratories has been automated fluorescent detection of DNA fragments
using DNA sequencers...Essentially, several DNA fragments can be labelled
simultaneously with a different fluorescent tag in a single reaction
tube (multiplex analysis) during the (PCR) amplification process. Automated
detection incorporates the technique of "real time analysis"
of DNA fragments as they migrate through a polyacrylamide gel past a
laser window which excites the fluorescent tag (fluorochrome) of the
fragment and detects the specific enhanced light using an array of CCDs
(charge coupled devices). DNA fragments are precisely sized ... calibrated
and entered into a digital computer base ...
... a major characteristic
of this detection method is the precision and accuracy afforded through
the use of an internal sizing standard run in the same lane (of the
gel) as each STR sample. The internal lane standard is recognized by
the computer and used to generate a fragment size calibration curve,
thereby providing an accurate quantitation of the amount of a fluorescent
signal (from the tagged fragment) and a precision standard for evaluating
any potential aberrant electrophoretic migration patterns. With the
aid of the computer and precise digital sizing data, the forensic scientist
evaluates each fragment with regards to match or nonmatch.(21)
PCR/STR profiling systems
are extremely sensitive and capable of analyzing a DNA sample as small
as 1 ng (1 nanogram = one- billionth of a gram); however, DNA samples
of 2-8 ng are considered optimal for the processing of numerous forensic
samples in the multiplex format described above.(22)
A simplified illustration
of the PCR/STR technology is shown in Figure 4.
Source: The Globe and
Mail, 19 July 1997, p. A6.
An important point regarding
the admissibility of DNA-typing evidence in court can be noted at this
point. Admissibility of evidence can be general or specific:
... refers to whether any evidence derived from the technique
in question should be introduced in court. Once a technique has gained
general admissibility, its results can still be ruled inadmissible if
they were obtained in an unreliable manner. General admissibility focuses
on reliability of the technique while specific admissibility
focuses on that of its results. (Emphasis in the original)(23)
The basic science and technology
behind forensic-DNA typing is not under serious question in Canada, or
elsewhere. The theory is scientifically sound and the technology used
to obtain DNA profiles is both well-established and evolving in accuracy
One of the most important
issues associated with forensic-DNA typing is the individuality of a so-called
It was noted above that a forensic-DNA profile does not represent the
complete genetic make-up of an individual; rather, it is a selection of
DNA fragments which can be used as identification markers. The key to
the usefulness of the DNA- typing procedure is the fact that the use of
"an appropriate number and combination of probes demonstrates that,
with the exception of identical twins, each individual (person) has a
assertion is not made as a consequence of an inclusive analysis of the
forensic-DNA profiles of the entire human population, or even of a small
fraction of the human population. The claim for uniqueness of a forensic-DNA
profile rests on statistical probabilities developed by population geneticists:
Finding that two samples
have the same DNA patterns does not necessarily mean they come from
the same individual, just as finding two specimens with the same blood
type does not mean they come from the same person. RFLP patterns represent
only a snapshot of the unique DNA sequence of each individual ... population
genetics is an essential element in forensic uses of all genetic techniques,
including DNA technologies.
The validity of forensic
DNA tests does not hinge on population genetics.
Interpreting test results, however, depends on population frequencies
of the various DNA markers ... In other words, population genetics provides
meaning - numerical weight - to DNA patterns obtained by molecular genetics
techniques. (Emphasis in the original)(26)
If a set of patterns produced
through forensic-DNA typing indicates a match between evidence from, say,
a bloodstain and a known DNA sample from a suspect or a victim, established
population frequencies of the RFLP or STR patterns are used to determine
the probability of the matchs having arisen randomly. Once the forensic
laboratory has matched RFLP or STR patterns from two samples of DNA an
analyst may estimate how frequently such a match might be expected to
arise by chance in a given population.
Two steps are involved in
this process. First, the frequency of the individual bands are ascertained
by examining random population samples. This step may be described as
a fundamentally empirical exercise, involving comparisons with established
data bases for various sub-populations. Such data bases (which do not
identify the individual sources of the DNA specimens) exist in Canada,
the United States, and elsewhere in the world.
The second step calls for
an estimate of the population frequency of the overall DNA pattern. In
contrast to the basic empiricism of the first step, the second step is
a fundamentally theoretical exercise which draws upon information and
procedures developed by population geneticists. The statistical significance
of forensic-DNA profiles, or fingerprints, in terms of their usefulness
in criminal and civil proceedings is an important subject.
A heated debate on this
issue has taken place in scientific journals, and in the news media, particularly
in the first half of the present decade. An extensive literature is now
available on the matter. In particular, two reports have been generated
by the United States National Research Council. The first - DNA Technology
in Forensic Science - was published in 1992.(27)
The second US-NRC report, The Evaluation of Forensic-DNA Evidence,
was published in 1996.(28)
The major controversy that
erupted over forensic-DNA typing - and which led to the two reports noted
above - concerned the statistical methods used, principally by population
geneticists, to interpret the significance of matching forensic-DNA profiles.
The probability that two forensic-DNA patterns could match entirely by
chance has been, and is, considered unlikely in the extreme.
An important issue in this
debate is the possible influence of population substructures on the significance
of individual profiles obtained with forensic-DNA technology. If human
matings were entirely random - that is, if individuals always wed, and
mated with, persons who were totally unrelated - there would have been
much less concern about the individuality of forensic-DNA profiles. However,
humans often do not mate randomly in most population subgroups.
In an extreme example, individuals
in an isolated community (for example on an island) would mate with persons
who were related in some way, perhaps as distant, or not-so-distant, cousins.
Similarly, marriages within the ethnic and racial communities in cities
and regions in both Canada and the United States are common, and often
lead to the mating of persons with a shared ancestry. The question inevitably
arises as to whether identical forensic-DNA profiles might be more likely
to be obtained from different individuals in such communities than in
the general population.
Most authorities now seem
to agree that this question has been adequately answered, and that forensic-DNA
profiles, even from a theoretical point of view, are acceptably specific
in identifying individuals when the technology is rigorously applied.
(It is even possible to identify siblings of the same sex using the current
technology.) The reliability of a profile increases with the number of
markers that are used: in RFLP analysis, for example, the use of five
markers (rather than three or four) greatly decreases - virtually to nil
- the likelihood that similar forensic-DNA profiles could be obtained
from different individuals.(29)
In Canada, the PCR/STR system
is seen as producing profiles that are highly individual and random matches
are judged to be very unlikely. The likelihood of a random match in the
system used by the RCMP is described by Dr. Fourney as follows:
A multi-DNA fragment match
in the (RCMPs) DNA analysis procedure is considered exceedingly
rare and extremely probative evidence. Currently the Royal Canadian
Mounted Police use three multiplex systems which have excellent discrimination
potential and (which are also) capable of gender determination. The
estimated frequency of the average genetic profile in the Canadian population
across (the) 10 STR loci (used in the system) is one in 94 billion.(30)
In most cases, it should
also be noted, a suspect will be associated with a crime scene by evidence
other than his/her forensic-DNA profile. The profile then becomes corroborating
evidence, and usually will not have to stand alone in the prosecutions
case. However, where the suspect is identified and apprehended entirely
on the basis of a forensic-DNA profile - as could happen through the use
of a forensic-DNA data base - concerns about the individuality of the
identifying profile rise accordingly.
With respect to the specific
admissibility of forensic-DNA evidence, the question is whether a
forensic-DNA profile has been developed using the appropriate technology,
and whether that technology has been rigorously applied. It is possible
that, as this technology becomes more widely used, the quality of individual
tests on samples might decline as demand rises to meet the evidentiary
needs of both the prosecution and the defence.
In Canada, most forensic-DNA
typing is done in government laboratories. In addition to the forensic
laboratories operated by the RCMP, which handle most such analyses in
Canada, DNA typing is also done by the Centre of Forensic Sciences in
Toronto and the Laboratoire de Police Scientifique in Montreal.(31)
There are several private laboratories operating in Canada and, in addition,
work is sometimes done by private United States laboratories under contract.
According to the RCMP, most private-laboratory work is done for civil
cases, particularly paternity cases, and for use by defence counsel. Arguably,
quality control is more readily achieved in Canada, because of the relatively
large government involvement, than in the United States, where private
companies are more widely operating.
The quality control, or
quality assurance of one organization will be described. TWGDAM, the Technical
Working Group on DNA Analytical Methods, first met in November 1988; the
meeting was hosted by the United States Federal Bureau of Investigation
(FBI) Laboratory and Academy. At that time, TWGDAM consisted of 31 scientists
representing 16 forensic laboratories in the United States and Canada
- including that of the RCMP - and two research institutions.(32)
The purpose of TWGDAM is
described by Inman and Rudin as follows:
together a select number of individuals from the forensic science
community who are actively pursuing the various DNA analysis methods;
the methods now being used;
the work that has been done;
guidelines where appropriate.(33)
TWGDAM has produced detailed
guidelines for forensic-DNA profiling: Guidelines for Quality Assurance
Program for DNA Analysis. The guidelines were first published in 1991;
they were updated in 1996.(34)
Finally, it can be noted
that, in addition to its use in human forensic work, forensic-DNA profiling
has found a place in wildlife research and casework, in Canada and elsewhere.
The technology can be used in a variety of applications, from species
identification based on bloodstains or meat samples, to estimating the
health of a population by determining the amount of inbreeding that might
have occurred. Poaching has placed the survival of many wildlife species
at risk. DNA typing based on small evidentiary specimens can be used in
cases involving poachers just as it can in cases involving murderers and
DNA DATA BANKS
Use of DNA Data Banks in Other Countries
During this century, thousands
of crimes have been solved through the use of automated systems that search
data banks for a match with unidentified latent fingerprints taken from
crime scenes. In Canada (and the United States) an Automated Fingerprint
Identification System (AFIS) conducts comparison searches against the
national repository of the fingerprint collection and a parallel repository
of latent fingerprint impressions from crime scenes. Criminal records
are generated from the fingerprint forms and entered on the Canadian Police
Information Centre (CPIC) computer to which Canadian police forces and
other accredited law enforcement agencies have direct access.(35)
Forensic DNA profiles are,
in terms of their use in identification, similar to fingerprints; as witness
the popular use of the term "DNA fingerprint." The ability of
forensic-DNA typing to link scene-of-the-crime evidence to a suspect is
well established and, as noted, has enabled authorities to obtain convictions
in a significant number of cases. The Solicitor General of Canada has
referred to the use of forensic-DNA typing to obtain "convictions
in hundreds of violent crimes."(36)
In the United States since 1986, forensic-DNA typing has been used in
more than 24,000 cases.(37)
The potential of DNA technology
to assist in solving crimes, particularly violent crimes where DNA evidence
is left at the scene, would be significantly enhanced by the creation
of forensic-DNA data banks, similar to those already in existence for
fingerprints. The possibility of establishing DNA data banks has been
widely discussed in Canada and elsewhere. In some jurisdictions, notably
the United States and the United Kingdom, forensic-DNA data banks already
have been established.
The United Kingdoms
computerized DNA data base is operated by the Forensic Science Service
(FSS) at Birmingham; it became operational in April 1995. The U.K. Criminal
Justice and Public Order Act 1994 empowers the police in the UK to
take DNA samples from anyone charged with a "recordable offence"
- which includes a wide variety of offences, including non-violent crimes
- whether or not the DNA was immediately relevant to the offence with
which the person was being charged.(38)
The DNA profiles used in the UK data base are being produced using the
PCR/STR technology, which, as noted earlier, is the technique that the
RCMP is adopting in Canada. In 1995, the UK data base was expected to
contain 4 million DNA profiles by the year 2000.(39)
The UKs forensic-DNA
data bank has been used extensively:
...more than 50,000 STR
(short tandem repeat) samples have been added to their National Offender
Database and helped to solve more than 1,500 crimes that previously
had no prime suspect.(40)
Most, if not all, states
in the United States now have legislation in place mandating the collection
and analysis of samples for DNA data banks. Generally, DNA samples in
that country are collected from convicted felons, particularly rapists,
upon their release from prison. The rationale for this approach is that
a relatively small number of people are responsible for a disproportionately
large number of violent crimes; some studies have suggested that the recidivism
rates for some crimes, after imprisonment, may be as high as 50%. DNA
samples are typically sent to the state forensic-DNA laboratory for typing
and storage. The FBI is leading the effort in the United States to create
a national data bank, and pilot programs have been implemented.(41)
A Proposed Canadian DNA Bank
The first phase of the federal
governments legislative strategy involving forensic-DNA typing was
implemented on 13 July 1995, when Bill C-104, An Act to amend the Criminal
Code and the Young Offenders Act (forensic-DNA analysis), came into force.
That legislation permitted authorities, under warrant, to take DNA samples
from suspects in certain crimes.
On 10 April 1997, the Canadian
federal government introduced in the House of Commons Bill C-94, the DNA
Identification Act, to create a national data bank containing DNA
profiles from convicted offenders:
The new law will require
persons convicted of designated offences to provide samples of bodily
substances for forensic-DNA analysis, with the resulting profiles maintained
in a national DNA bank.
The data bank will consist
of a convicted offenders index that will contain DNA profiles
of adult and young offenders convicted of designated Criminal Code
offences, and a crime scene index that will contain DNA profiles
obtained from unsolved crime scenes.(42)
When introducing Bill C-94,
the Solicitor General, Mr. Gray, said:
Canada will be one of
only a handful of countries in the world to have a national DNA data
bank. This will give us a powerful investigative tool that will protect
Canadians from violent criminals. It will help ensure that those guilty
of serious crimes, such as repeat sex offenders and violent offenders,
are identified and apprehended more quickly while excluding innocent
The designated Criminal
Code offences under the bill would have been divided into primary
and secondary lists. The primary list would have included the most serious
violent offences, including sexual offences. Upon conviction of an accused,
the court would have ordered his or her bodily substances to be obtained
for the purpose of data banking. The list of primary offences was as follows:
- sexual interference (s. 151)
- invitation to sexual touching (s. 152)
- sexual exploitation (s. 152)
- incest (s. 155)
- offence in relation to juvenile prostitution
- murder (s. 235)
- manslaughter (s. 236)
- causing bodily harm with intent (s. 244)
- assault causing bodily harm or with a
weapon (s. 267)
- aggravated assault (s. 268)
- unlawfully causing bodily harm (s. 269)
- sexual assault (s. 271)
- sexual assault causing bodily harm or
with a weapon (s. 272)
- aggravated sexual assault (s. 273)
- kidnapping and forcible confinement (s.
- any offence under any of the following
provisions of the Criminal Code, chapter c-34 of the Revised
Statutes of Canada, 1970 as they read from time to time before 4 January
rape (s. 144)
sexual intercourse with a female under fourteen, between fourteen and
sixteen (s. 146)
sexual intercourse with feeble-minded (s. 148); and
- as they read before 1 January 1998; namely,
sexual intercourse with
step-daughter (paragraph 153(1)(a)).
The secondary list of designated
offences would have required samples for data bank purposes, upon court
order, following conviction of secondary offences where the judge was
satisfied that such an order was in the interests of public safety;
- piratical acts (s. 75)
- highjacking (s. 76)
- endangering safety of aircraft or airport
- seizing control of ship or fixed platform
- using explosives (s. 81(1)(a))
- causing death by criminal negligence
- causing bodily harm by criminal negligence
- failure to stop at the scene of an accident
- assault (s. 266)
- torture (s. 269.1)
- assaulting a police officer (s. 270(1)(a))
- hostage taking (s. 279.1)
- robbery (s. 344)
- breaking and entering with intent, committing
offence or breaking out (s. 348(1))
- mischief - that causes actual danger
to life (s. 430(2))
- arson (s. 433 & s. 434.1) and
- an offence under any of the following
provisions of the Criminal Code as it read from the time before
1 July 1990; namely:
s. 433 - arson
s. 434 - setting fire to other substance, and
- attempt or conspiracy to commit any of
Under Bill C-94, young offenders
would have been treated in the same way as adults for the purposes of
inclusion in the DNA data bank; and their DNA profiles while in the bank
would have been governed by the same rules of access. Unlike the situation
for adults, however, the periods of retention for the DNA profiles of
young offenders would have paralleled provisions for police records set
out in the Young Offenders Act. For adults, profiles would have
been retained indefinitely, unless the conviction were reversed or the
offender were granted a pardon.
The proposed data bank legislation
had a number of other features. DNA samples could have been collected
retroactively from currently sentenced offenders under two circumstances:
first, where an offender had been declared a "dangerous offender"
under Part XXIV of the Criminal Code; or, second, where an offender
had been convicted of more than one sexual offence, and was currently
serving a term of two years of more, even if on parole. There was also
a provision for "retrospective application," where a judge,
in the interests of public safety, could have ordered that a DNA sample
be taken from persons charged with a designated offence prior to the legislation
coming into effect and convicted afterwards.
Bill C-94 would also have
provided for restrictions on access to DNA samples and on data collected
under the legislation:
Stringent rules will govern
the collection, use and retention of DNA profiles and biological samples.
Access to DNA profiles contained in the convicted offenders index and
to samples will be strictly limited to those directly involved in the
operation of the data bank. Only the name attached to the profile will
be communicated to the appropriate law enforcement authorities for the
purpose of investigating criminal offences. Criminal penalties will
also be created to guard against any misuse or abuse of DNA profiles
or biological samples.(44)
Although Bill C-94 died
when the Prime Minister called the federal election on 27 April 1997,
Solicitor General Andy Scott said that similar legislation would be introduced
in the new session of Parliament beginning in September 1997.(45)
The various points of view on the legislation, including those noted below,
will be debated at that time.
It should be noted that
the costs associated with a proposed national forensic-DNA data bank would
be substantial. The technology is at the cutting edge, and is expensive.
Forensic DNA profiles can be computerized, however, which would produce
operational efficiencies. Also, the PCR/STR technology that is being adopted
in Canada by the RCMP will cost less than the older RFLP (restriction
fragment length polymorphism) technology, although the precise amount
of savings is not yet known. The start-up costs for the data bank are
estimated at $2.9 million, and it is anticipated that annual operating
costs would about $3.0 million.(46)
Predictably, there is a
divergence of opinion in Canada on how the DNA data bank should be organized
and run. In the following paragraphs, a sense of the contrasting views
will be presented, through the positions of the Privacy Commissioner of
Canada, the Canadian Bar Association, and the Canadian Police Association.
The Privacy Commissioner
of Canada (PCC), while supporting the use of forensic-DNA analysis to
aid police in apprehending violent criminals, has expressed reservations
about the creation of a forensic-DNA data bank and about how such a data
bank might be used. An individuals right to privacy, "privacy"
being interpreted as including the individuals unique DNA characteristics
and genetic make-up, lies at the heart of the PCCs concerns:
We acknowledge the value
of RFLP (restriction fragment length polymorphism) analysis in solving
crimes of violence. We accept its potential utility when authorized
by statute and when sufficient care is taken to ensure the accuracy
of the information generated by the analysis. But we strongly oppose
a government cataloguing the identifying genetic characteristics of
the overwhelmingly non-criminal male population (as has been considered
in the United Kingdom).(47)
The PCC has expressed concern
about the creation and use of a forensic-DNA data bank by the police to
apprehend criminals. As an example, the Commissioner has cited the Pitchfork
case in the UK (noted earlier in this paper). In an attempt to solve the
sex murders of two teenage girls, the UK police had amassed, through a
voluntary program, more than 3,600 forensic DNA profiles of males from
the local area where the crimes occurred; later, the police used this
ad hoc "data bank" to apprehend the perpetrator of a
...the (DNA) samples were
not used for (the Pitchfork) investigation alone. Police officers later
matched a DNA print from one of the volunteers to a semen sample from
a previous unsolved rape. For the police, this was merely clever sleuthing.
For civil libertarians, it raised the spectre of future population databases
of genetic characteristics, not merely identification features, being
used as another instrument of control in society.(48)
An observer might well agree,
however, that the apprehending of a rapist through this use of forensic-DNA
technology was indeed "clever sleuthing." Furthermore, because
an individuals forensic-DNA profile gives no information on that
persons "genetic characteristics" a possible exception
being that the PCR/STR technology being phased in by the RCMP will determine
the individuals gender the same observer might also ask whether
the "spectre of future population databases of genetic characteristics"
is a realistic fear.
Nonetheless, the PCC made
a recommendation (in his 1995 report), the first part of which states:
Governments should not
establish banks of genetic samples of convicted persons or the general
population for criminal justice purposes. Governments should not establish
genetic databases of the general population for criminal justice purposes.(49)
However, in the second part
of this recommendation, the Commissioner appears to soften this viewpoint:
If genetic databases are
found to be acceptable, they should only be used for identification.
The information contained in a genetic database and any genetic samples
related to the crime should not be used to try to identify other characteristics
that may have a genetic link, such as personality.(50)
In fact a forensic-DNA data
bank, such as was proposed by the federal government in Bill C-94, would
not use the genetic material for anything other than identification purposes
in the apprehending of criminals. The PCCs point is well taken,
however; a data bank established for purposes of identification should
not be used for other, greatly expanded, purposes, particularly those
with a rationale as fragile as attempting to link an individuals
genetic complement with personality traits that might be judged, rightly
or wrongly, as indicating criminal potential.
In its 1995 response to
the Department of Justice consultation paper Obtaining and Banking
DNA Forensic Evidence, the Office of the PCC appears to have accepted
the federal governments proposal to establish a forensic-DNA data
bank, although with some restrictions on sampling, use of the DNA profile,
and disposition of the DNA sample after use. Some of the suggested restrictions
by the PCC are listed below.
The DNA sample should be
collected by a health-care professional.
should not be collected unless the information is relevant to the
crime in question, the crime must involve violence or the likelihood
of violence, and the collection must be authorized by a judge.
The PCC also discussed whether
the DNA data bank should be used to solve crimes other than the crime
for which the DNA sample was originally obtained:
After conviction (of the
individual), DNA information could be used, without a court order, to
seek a connection with any unsolved crime of a similar nature. For example,
genetic information from the DNA of someone convicted of a sexual assault
could be used to look for a match with unsolved sexual assaults. Use
of the DNA to resolve crimes that are not of the same nature as the
one for which the person was convicted, should require a judges
approval. This would prevent a fishing expedition.
It is not clear from the
PCCs brief, however, why a "fishing expedition" would
be an unacceptable use of the DNA data bank. That is, what are the specific
objections to linking the banked forensic-DNA profile of a person convicted
of robbery with the DNA profile obtained from the scene of a more serious
crime, such as rape or murder, especially if that link led to the individuals
arrest and conviction for the more serious offence?
Canadian Bar Association
The National Criminal Justice
Section of the Canadian Bar Association (hereafter, the Section) supports
the creation of a national DNA data bank "provided it is established
with appropriate respect for the liberty and privacy interests of individuals."(51)
The Section proposes a number of limitations and safeguards on collection,
retention and use of DNA samples, and these are summarized below.
recommends that a forensic-DNA data bank be used for the limited purpose
of "providing police with reasonable grounds to obtain a search
warrant for another bodily fluids sample, where a match is found between
the DNA of an unknown sample and a DNA sample held in the data bank."
The rationale for this recommendation is that the data bank match
in and of itself may not be reliable as evidence in court.
recommends, as a balance between privacy interests and the need to
protect society, that the data bank should only contain DNA profiles
only for crimes such as "homicide and serious sexual and violent
offences, including breaking and entering and committing a sexual
In the cases
of young offenders, the Section recommends that DNA profiles should
be maintained only for a limited period of time, if there has been
no further related offence. However, exceptions to this rule may be
made for serious violent crimes committed by young offenders, and
the DNA retained for an indefinite period.
"strongly opposes the seizing of (DNA) samples upon arrest,"
unless a warrant has been obtained. The Sections opposition
is based on the view that a seizure of a DNA sample before conviction
is constitutionally unsound. (Under current legislation, fingerprints
and photographs of the accused may be taken at the time charges are
believes that police officers can be trained to take samples for DNA
analysis, after conviction of an accused. The Section cites examples
of some police agencies (for example, the Vancouver City Police) who
have a training program and a standard kit for blood sample collection.
However, if the sample is taken in prison, the Section believes that
"prison health professionals" should be responsible for
taking the sample.
shares the belief of the Privacy Commissioner of Canada that DNA samples
should not be retained in a national data bank; only the results of
the analysis, the forensic-DNA profile, should be retained. The concern
of the two organizations is the same; namely, that the existence of
a collection of DNA samples might constitute an "invitation"
for inappropriate research into the possible linkages between genes
and criminal behaviour.
Canadian Police Association
The value of forensic-DNA
typing to the police, and by extension to the criminal justice system,
has been proven in many criminal investigations. Not only has the technology
linked criminals to particular crimes, it has also been used successfully
to exonerate individuals who have been wrongly convicted, the cases of
Guy Paul Morin and David Milgaard being the best known in this country.
It is not surprising, therefore, that police agencies want the collection
of DNA samples, and the operation of a national data bank, to be as efficient
and as comprehensive as possible.
The Canadian Police Association
believes that the same preconditions and restrictions should apply to
the collection and retention of forensic DNA profiles as currently apply
to fingerprints under the Identification of Criminals Act:
...like fingerprints before
them, DNA samples have a dual investigative relevance. First, they are
a method by which a person suspected of a specific crime can be either
linked or eliminated through comparison with a trace or crime scene
sample such as semen, hair or blood. Second, and far more importantly
where there is no evidence suggesting a particular individual, crime
scene evidence could be matched to previously held DNA evidence contained
in a DNA Data Bank. In this sense, DNA evidence is exactly analogous
to fingerprints in that they are in existence because of a statutorily
authorized threshold of prior activity which has led to the retention
of the record in the first place. ... their forensic investigative value
is profound. Failure to make full use of both the gathering of such
material and retention is nothing short of irresponsible given the undeniable
alternative of non-prosecution of most serious crimes.(52)
The concern expressed by
the Office of the Privacy Commissioner of Canada that DNA samples might
be used for research into the genetic basis of criminal behaviour are
summarily dismissed by the Police Association as "unjustifiable."
The Associations brief does not suggest, however, that DNA samples
should be used for purposes other than the identification of suspects
A major point of disagreement
between the Canadian Police Association and both the Privacy Commissioner
of Canada and the Canadian Bar Association is on the question of when
the DNA sample should be collected. As noted above, both the PCC and the
National Criminal Justice Section of the CBA have argued that DNA samples
should not be seized at the time of arrest, but only after conviction.
The Police Association argues that the sample should be taken at the time
of the arrest, as is done with fingerprints. Moreover, the Police Association
would support, and even expand, the list of designated offences for which
DNA samples could be collected. The Association has suggested a possible
scenario which, in its view, supports the taking of a DNA sample at the
time of arrest, even for a relatively "minor" offence.
In essence, we advocated
that the current law, pursuant to the Identification of Criminals
Act, which permits taking of offender information (fingerprints)
at time of arrest for indictable offences, was exactly the process which
must be followed with the technological upgrade which DNA samples represent.
This process of taking information prior to conviction ensures that
the material will be obtained, unlike a process which allows taking
of samples following conviction...
Our criminal justice system
grants bail to over 95% of persons charged with criminal offences. If,
to use a common example, a person is charged with a break and enter
but is actually, unknown to police, responsible for a string of unsolved
rapes in which trace evidence exists, he will be released without DNA
samples being taken. The offender will know that the only way his DNA
will be obtained, and (he will) be captured for rapes, is if he returns
and is convicted on the original charge. Does anyone really believe
that such persons will not fail to appear for court?(53)
The Association cites a
statistic to the effect that, in 1995, more than 66,000 people in Canada
either broke bail or failed to appear as required. Also, the Association
says that in Canada,
...warrants issued for
people who fail to appear on such charges as break and enter are not
generally returnable throughout Canada. What this means is that if the
same undetected rapist for whom a break and enter warrant is outstanding
in Ottawa, is picked up in Alberta, current practice is that he would
not be returned to face the "minor" break and enter charge.(54)
Overall, the Canadian Police
Association is of the opinion that the proposed legislation would not
have gone far enough in creating an optimally effective DNA data bank.
In the "open letter" to Members of Parliament cited above, the
Associations president urged rejection of Bill C-94 as drafted,
and the introduction of more comprehensive and effective legislation.
As was the case with fingerprints,
forensic-DNA profiling has become an accepted, and now probably indispensable,
technology in forensic science. The rapidity of its acceptance - it is
only eleven years since the Pitchfork murder case was resolved - reflects
the technologys solid foundation in molecular genetics. This foundation
accounts for the technologys formidable, and rarely challenged,
reputation for accurate identification based on objective observations.
As noted earlier, forensic-DNA profiling can reach back over the decades
- and even centuries - to answer important questions of identity and lineage
through the use of the genetic code.
Equally impressive has been
the rapid evolution of the technology. In 1986, the forensic-DNA profiles
that ultimately resolved the Pitchfork murders (first by exonerating the
innocent self-confessed suspect, and second by confirming the guilt of
Pitchfork himself) were complicated, time-consuming, and labour-intensive.
Today, using the leading-edge type of automated PCR/STR technology being
adopted by Canadas RCMP, profiles can be developed in much less
time, and with much improved discrimination capability.
The technology undoubtedly
will continue to evolve, with expectations of increased efficiency, wider
applicability, and - it is hoped - lower costs for each forensic-DNA profile
developed. Dr. Fourney has suggested that future developments will see
the "the automation of the entire process from the extraction of
DNA to the generation and detection of discrete markers eventually leading
to a final digital entry into a database that is searchable."(55)
At the same time, he notes, there is a major challenge facing forensic
laboratories world-wide: the adoption of a common set of standards for
On the other hand, as the
technology finds a greater degree of application, within forensic science
and beyond, total costs to society for the use of the technology may well
increase, even as unit costs decline. The question of the benefits versus
the costs of using the technology will no doubt arise and come under close
examination, particularly by governments.
A great advantage of forensic-DNA
technology is, as noted, that it is based on objective science; the more
it becomes automated and removed from the possibility of human error,
the greater will be its objectivity. In recent months, police forces and
forensic laboratories in both Canada and the United States have come under
pronounced criticism for their mishandling of criminal investigations.
The Milgaard, Morin and Bernardo cases are the most notorious in this
The Morin case, in particular,
witnessed a failure in the application of forensic science, particularly
in the analysis of fibre evidence, which involves a degree of subjective
interpretation. Forensic-DNA analysis, as noted, led to the exoneration
of Guy Paul Morin and others, in situations where traditional technologies
and methods had failed, for whatever reason.
There will very likely be
more examples in this vein. While a positive forensic-DNA match is persuasive
evidence of a suspects association with a crime, it is not absolute
proof. There is always a chance, however slight, that the match might
be a random one: it is impossible to prove a negative, and statistical
probability cannot be ignored. Additional evidence and information is
usually required to obtain a conviction. However, a negative forensic-DNA
match, referred to as an exclusion, is absolute. In this context,
it is significant that the FBI in the United States has reported that
"fully 1/3 of all suspects in rape cases are released before trial
because DNA evidence exonerates them."(57)
Even if this figure may be slightly exaggerated, as Inman and Rudin suggest,
the power of the technology to prove innocence cannot be denied. In all
cases where forensic-DNA technology is used, however the possibility of
human error - particularly sample mix-ups has to be guarded against.
Any technology is only as reliable as the persons using it.
Finally, there are a number
of projects under way in the United States, Canada, and elsewhere that
are making use of forensic-DNA technology to free the innocent from incarceration.
The original initiative here has been the Innocence Project at the Benjamin
N. Cordozo School of Law at Yeshiva University in New York City. In Canada,
the Osgoode Hall Law School at York University in Toronto will launch
a similar project. In this effort, the York University group will work
with the Association in Defence of the Wrongly Convicted (AIDWYC) in Scarborough,
one of the four building blocks of DNA, indicated by the letter A.
Automated Fingerprint Identification System.
gel medium used for separating DNA fragments.
one of two or more alternative forms of a gene or a genetic marker.
applied to DNA, it is the process of making multiple copies of a DNA sequence
using the polymerase chain reaction (PCR).
also called autoradiograph or autorad; an x-ray film on
which radioactive or chemiluminescent probes have left an image determining
the position of specific DNA fragments. Sometimes described as a "genetic
any chromosome other than the X and Y sex chromosomes.
the visual image of a specific DNA fragment on an autorad. (The "bar"
in the bar code.)
in this context, a subunit of nucleic acid. The four bases are adenine,
thymine, cytosine and guanine, indicated by the letters
A, T, C and G.
the "rungs" of the DNA "ladder" are composed in part
of base pairs. Adenine always pairs with thymine; cytosine with guanine.
the nuclear structure, visible under a microscope, that contains the genes
which are transmitted from one generation to the next.
that region of the DNA that carries genetic information that has the capability
of producing a protein. (Opposite - Noncoding.)
one of the four building blocks of DNA, indicated by the letter C.
the separation of double-stranded DNA into two complementary single strands
by heat or chemical means; an essential step in forensic-DNA profiling.
DNA: the genetic material of most
organisms, including humans.
the state of having two sets of chromosomes, in pairs; humans have 23
chromosomes in pairs, for a total of 46, in all adult cells, except for
germ cells. (See haploid.)
an enzyme that synthesizes DNA from an existing template. (See polymerase
chain reaction or PCR.)
a short segment of DNA labelled with a radioactive or chemical tag that
is used to detect the presence of a particular DNA sequence or fragment.
A technique, used in forensic-DNA profiling, in which the DNA fragments
are separated according to size by their rate of movement in an electric
field through a gel.
a protein catalyst of a specific biochemical reaction; in forensic-DNA
work, some of the enzymes used are restriction nucleases and DNA polymerase.
a type of cell, including most human cells, that contains a nucleus, which
in turn contains the chromosomes.
a semi-solid matrix, usually agarose or acrylamide, used in electrophoresis
to separate molecules by size. (gel electrophoresis)
Genetic Marker, Marker:
a defined location on a chromosome having known genetic characteristics.
the total genetic makeup of an organism.
one of the four building blocks of DNA, indicated by the letter G.
a restriction enzyme, or restriction endonuclease, used in RFLP analysis;
the standard enzyme used in Canada and the United States.
having one set of chromosomes. (See diploid.) Sperm and egg cells
having a different allele (or version) of a gene at a particular locus
on each chromosome in a pair, in a diploid organism. (The opposite is
having the same allele (or version) of a gene at a particular locus on
both chromosomes in a pair, in a diploid organism. (The opposite is heterozygous.)
a DNA locus that shows extreme variation between people. Forensic-DNA
analysis is based on such variability in the DNA.
the specific physical location of a gene, or specific DNA sequence, on
a region of DNA which does not code, meaning that it lacks the capacity
to produce a protein.
an organelle found in eukaryotic cells, including human cells, in which
are found the chromosomes.
polymerase chain reaction.
a polymer which, formulated as a gel, is used to separate small DNA fragments
in an electrophoretic field.
Polymerase Chain Reaction
(PCR): a process mediated by a
DNA polymerase, yielding millions of copies of a desired DNA sequence.
the presence of multiple alleles of a gene in a population.
a short segment of synthetic tagged DNA, used to detect a specific DNA
fragment or sequence.
a cell lacking a nucleus; all prokaryotes are bacteria. (See eukaryote.)
Restriction Enzyme, Restriction
Endonuclease: an enzyme that cuts
DNA at specific locations determined by the particular DNA sequence.
Length Polymorphism (RFLP):
variation in the length of DNA fragments produced by a restriction enzyme
that cuts the DNA at a polymorphic locus. The polymorphism may be in the
restriction enzyme site or in the number of tandem repeats between the
cut points. Variable Number Tandem Repeats (VNTR) loci are used in forensic-DNA
short tandem repeat.
repeating units of an identical DNA sequence arranged in succession in
a particular region of a chromosome.
one of the four building blocks of DNA, indicated by the letter T.
Variable Number Tandem
Repeats (VNTR): repeating
units of an identical DNA sequence, arranged in succession in a particular
region of a chromosome; the number of repeats varies between individuals,
which makes forensic-DNA identification possible.
Quoted in: National Research Council (U.S.), The Evaluation of DNA Evidence,
National Academy Press, Washington, D.C., 1996, p. 1-1.
Marie Lussier, "Tailoring the Rules of Admissibility: Genes and Canadian
Criminal Law," The Canadian Bar Review, Vol. 71, June 1992,
David Roberts and Kirk Makin, "DNA Test Exonerates Milgaard,"
The Globe and Mail (Toronto), 19 July 1997, p. A1.
Stephen Strauss, "Canadian Testing Incompetent, U.S. Expert Says,"
The Globe and Mail (Toronto), 22 July 1997, p. A4.
Alanna Mitchell and David Roberts, "Fisher Charged in 1969 Sex Slaying,"
The Globe and Mail (Toronto), 26 July 1997, p. A1.
Lussier (1992), p. 327.
J.D. Watson and F.H.C. Crick, "Molecular Structure of Nucleic
Acids," Nature, Vol. 171, 1953, p. 737-738.
J. Robertson, A.M. Ross, and L.A. Burgoyne, Editors, DNA in Forensic
Science, Ellis Horwood Publisher, 1990, p. 24. (The actual percentage
of non-coding DNA is not known with accuracy. The estimate provided in
this source is 98.5%.)
Paul Berg and Maxine Singer, Dealing with Genes - The Language of Heredity,
University Science Books, 1992, p. 138.
Where a specific gene occurs in two or more forms, the different forms
are known as alleles. A person may be homozygous or heterozygous for a
Berg and Singer (1992), p. 153.
Ibid., p. 156. (The discoverer of the polymerase chain reaction,
Dr. Karry Mullis, was awarded the Nobel Prize in 1993.)
National Research Council (U.S.) (1996), p. 2-11.
Ron N. Fourney, "Forensic Reality and the Practical Experience of
DNA Typing," Canadian Police Chief Magazine, 1996, p. 48.
Dermot O'Sullivan, "Romanov Riddle: DNA Tests Identify Bones of Czar
and Family," Chemical & Engineering News, 19 July 1993,
p. 6-7. (The mystery of the Princess Anastasia remains unresolved. However,
most accounts of the execution say that the bodies of Anastasia and her
brother, Prince Alexei, were burned and buried separately.)
Strauss (1997), p. A6.
RCMP, personal communication, May 1997.
National Research Council (U.S.) (1996), p. 2-11.
Fourney (1996), p. 48.
Keith Inman and Norah Rudin, An Introduction to Forensic DNA Analysis,
CRC Press, 1997, p. 48.
Fourney (1996), p. 50.
Lussier (1992), p. 340.
Although the term "DNA fingerprint" is not officially used,
it continues to be a convenient shorthand term for journalists and writers
both inside and outside the scientific community. The RCMP originally
used this term but stopped doing so, partly because of confusion with
conventional fingerprinting, which resulted in mis-routing of mail and
inquiries within the organization.
Barry D. Gaudette, "DNA TYPING - A New Service to Canadian Police,"
RCMP Gazette, Vol. 52, No. 4, 1990, p. 2.
United States Congress, Genetic Witness: Forensic Uses of DNA Tests,
Office of Technology Assessment, Washington, D.C., 1990, p. 66.
National Research Council (U.S.), DNA Technology in Forensic Science,
Victor A. McKusick, Chairman, National Academy of Sciences, Washington,
D.C., April 1992.
National Research Council (U.S.), The Evaluation of DNA Evidence,
National Academy Press, Washington, D.C. (1996).
Ibid., p. 4-23.
Fourney (1996), p. 50.
The RCMP has a formal link on DNA typing to its American counterpart,
the FBI, through participation in The Technical Working Group on DNA Analytical
Methods (TWGDAM), a North American organization which meets three times
a year at the FBI Academy in Quantico, Virginia.
Inman and Rudin (1997), p. 188. The comparable European Technical
Working body is EDNAP, the European DNA profiling group.
Ibid, p. 188-189.
Royal Canadian Mounted Police, Information and Identification Services
Directorate, see web site - http://www.rcmp-grc.gc.ca.
Government of Canada, "Herb Gray and Allan Rock Introduce Bill to
Establish a National DNA Data Bank," Press Release, 10 April
Inman and Rudin (1997), p. 21.
Patsy Hughes, "DNA Fingerprinting," Research Paper 96/44, Science
and Environment Section, House of Commons Library (UK), 27 March 1996,
Charles Arthur, "Suspects DNA goes on file," New Scientist,
25 March 1995, p. 7.
Fourney (1996), p. 44.
Inman and Rudin (1997), p. 133-134. (The US armed forces have also
instituted a DNA collection program from military personnel, through the
Armed Forces DNA Identification Laboratory, AFDIL. This data bank is directed
toward the identification of victims of war, and military exercises.)
Government of Canada, "Herb Gray and Allan Rock Introduce Bill to
Establish a National DNA Data Bank," Press Release, 10 April 1997.
Keith McArthur, "Proposal to Set up a DNA Bank Will Be Retabled,"
The Globe and Mail (Toronto), 12 September 1997.
RCMP, Personal Communication, 9 May 1997.
The Privacy Commissioner of Canada, Genetic Testing and Privacy, Ottawa,
1995, p. 48. (At the time of writing, RFLP analysis was the principal
forensic DNA technology being used in Canada.)
Ibid, p. 50, Recommendation No. 11.
National Criminal Justice Section, the Canadian Bar Association, DNA
Data Banking, April 1996, p. 12.
The Canadian Police Association, DNA Data Bank Amendments - A Response
to the Solicitor Generals Consultation Document (undated), p. 1-2.
Neal Jessop, President, The Canadian Police Association, "An Open
Letter to all Members of Parliament," The Hill Times, 14 April
Fourney (1996), p. 50.
Editorial, "On Guard for Thee?" The Globe and Mail (Toronto),
22 July 1997.
Inman and Rudin (1997), p. 21.
Kirk Makin, "Police Tunnel Vision Gives No Justice, Critics
Say," The Globe and Mail (Toronto), 22 July 1997, p. A1,