When the results obtained from the standard sample from a known individual are all consistent
with or are all present in the results from the unknown crime scene sample, then the results are
considered an inclusion or nonexclusion. The term “match” is also commonly used when the test
results are consistent with the results from a known individual. That individual is included (cannot be excluded) as a possible source of the DNA found in the sample. Often, statistical frequencies regarding the rarity of the particular set of genetic information observed in the unknown
evidence sample and for a known individual are provided for various population groups.
It is possible for a falsely accused individual to be included as a source of a sample, particularly
if the test system used only tests at one or a few loci (e.g., the DQα). In this situation, additional
testing at more loci should be performed with the remaining evidence and/or DNA.
for that particular case from a legal perspective. Situations where this might apply are when the
results obtained are all consistent with the individual from whom the samples were collected
Exclusions
When the results obtained from the standard sample from a known individual are not all present in the results from the unknown crime scene sample, the results are considered an exclusion, a
nonmatch, or noninclusion. With limited exceptions, an exclusion of an individual at any one
genetic region eliminates that individual as a source of the DNA found in the sample.
In some cases where an exclusion is reported, it may be necessary to do additional testing for
that exclusion to be meaningful to the case or to provide evidence for exoneration. A situation
where this might apply is when the defendant is excluded as a donor of the DNA in a sexual
assault case, but no samples are available from the victim and/or consensual partners.
Inconclusive Result
Results may be interpreted as inconclusive for several reasons. These include situations where
no results or only partial results are obtained from the sample due to the limited amount of suitable human DNA or where results are obtained from an unknown crime scene sample but there
are no samples from known individuals available for comparison. In the latter case, the results
would be suitable for comparison once an appropriate sample for comparison is tested.
Database
RFLP-based and PCR-based databases have been constructed and are continuing to be expanded
in many laboratories throughout the United States and the world with samples from convicted
sex offenders and convicted felons, as well as samples from unsolved crimes. These databases
will be especially helpful for linking previously unrelated cases and for screening a large number
of known individuals already convicted of a crime to newly tested crime scene samples.
DNA databases of mitochondrial sequences are being established that are currently being used
for statistical purposes. It is possible that databases containing mitochondrial sequences may be
constructed for comparison to crime scene samples in the future.
Testing in the Future
Testing of hair shafts using mitochondrial DNA sequencing likely will become more widely
available in the immediate future. It may be possible to isolate and test DNA from other samples
that are not routinely tested today (e.g., fingerprints).
Y-specific probes are sequences of DNA found only on the Y (or male) chromosome. Development and validation of these probes are in progress. These probes will be especially useful for
mixed samples in which the female component is not relevant or may make interpretation of the
results more difficult (e.g., sexual assault samples, fingernails from female victims when the
assailant is male) and in the analysis and determination of the number of male sources of DNA in
samples where there are multiple male contributors (e.g., multiple assailants and/or consensual
partners in sexual assault samples). Because Y chromosomes are inherited through the male lineage, Y-specific probe results may be used to link a crime scene sample to a particular family.
DNA probes useful for identification testing are being developed from many other organisms and
may be useful in crime scene investigation. There are reported cases in which DNA from cat hair18
and from a particular type of plant has been used to link individuals to a particular crime scene.
Progress is being made in developing technologies for miniaturization of DNA tests (e.g.,
microchip analysis) that may be applied to forensic testing in the future. Expansion of existing
technologies (e.g., sequencing of nuclear DNA) may emerge for forensic testing. Other as yet
unknown or undeveloped technologies may be forthcoming that could be applied to forensic
testing. It is likely that future tests could increase the sensitivity and speed of testing, as well
as increase the discrimination capability of a test to unique identification of an individual.
with or are all present in the results from the unknown crime scene sample, then the results are
considered an inclusion or nonexclusion. The term “match” is also commonly used when the test
results are consistent with the results from a known individual. That individual is included (cannot be excluded) as a possible source of the DNA found in the sample. Often, statistical frequencies regarding the rarity of the particular set of genetic information observed in the unknown
evidence sample and for a known individual are provided for various population groups.
It is possible for a falsely accused individual to be included as a source of a sample, particularly
if the test system used only tests at one or a few loci (e.g., the DQα). In this situation, additional
testing at more loci should be performed with the remaining evidence and/or DNA.
for that particular case from a legal perspective. Situations where this might apply are when the
results obtained are all consistent with the individual from whom the samples were collected
Exclusions
When the results obtained from the standard sample from a known individual are not all present in the results from the unknown crime scene sample, the results are considered an exclusion, a
nonmatch, or noninclusion. With limited exceptions, an exclusion of an individual at any one
genetic region eliminates that individual as a source of the DNA found in the sample.
In some cases where an exclusion is reported, it may be necessary to do additional testing for
that exclusion to be meaningful to the case or to provide evidence for exoneration. A situation
where this might apply is when the defendant is excluded as a donor of the DNA in a sexual
assault case, but no samples are available from the victim and/or consensual partners.
Inconclusive Result
Results may be interpreted as inconclusive for several reasons. These include situations where
no results or only partial results are obtained from the sample due to the limited amount of suitable human DNA or where results are obtained from an unknown crime scene sample but there
are no samples from known individuals available for comparison. In the latter case, the results
would be suitable for comparison once an appropriate sample for comparison is tested.
Database
RFLP-based and PCR-based databases have been constructed and are continuing to be expanded
in many laboratories throughout the United States and the world with samples from convicted
sex offenders and convicted felons, as well as samples from unsolved crimes. These databases
will be especially helpful for linking previously unrelated cases and for screening a large number
of known individuals already convicted of a crime to newly tested crime scene samples.
DNA databases of mitochondrial sequences are being established that are currently being used
for statistical purposes. It is possible that databases containing mitochondrial sequences may be
constructed for comparison to crime scene samples in the future.
Testing in the Future
Testing of hair shafts using mitochondrial DNA sequencing likely will become more widely
available in the immediate future. It may be possible to isolate and test DNA from other samples
that are not routinely tested today (e.g., fingerprints).
Y-specific probes are sequences of DNA found only on the Y (or male) chromosome. Development and validation of these probes are in progress. These probes will be especially useful for
mixed samples in which the female component is not relevant or may make interpretation of the
results more difficult (e.g., sexual assault samples, fingernails from female victims when the
assailant is male) and in the analysis and determination of the number of male sources of DNA in
samples where there are multiple male contributors (e.g., multiple assailants and/or consensual
partners in sexual assault samples). Because Y chromosomes are inherited through the male lineage, Y-specific probe results may be used to link a crime scene sample to a particular family.
DNA probes useful for identification testing are being developed from many other organisms and
may be useful in crime scene investigation. There are reported cases in which DNA from cat hair18
and from a particular type of plant has been used to link individuals to a particular crime scene.
Progress is being made in developing technologies for miniaturization of DNA tests (e.g.,
microchip analysis) that may be applied to forensic testing in the future. Expansion of existing
technologies (e.g., sequencing of nuclear DNA) may emerge for forensic testing. Other as yet
unknown or undeveloped technologies may be forthcoming that could be applied to forensic
testing. It is likely that future tests could increase the sensitivity and speed of testing, as well
as increase the discrimination capability of a test to unique identification of an individual.