Gene Cloning

416 Gene Cloning
Box 13.1 DNA Profile Databases
The primary DNA profile database in the UK is the National DNA Database
(NDNAD) which is run by the Forensic Science Service on behalf of the
Association of Chief Police Officers. In the United States the equivalent
database is the Combined DNA Index System (CODIS) which is maintained
by the FBI. Each of these databases contains over 2.5 million DNA
profiles, most of which have been obtained from individuals arrested for,
or convicted of, serious offences. A smaller proportion of the profiles in
each database are forensic profiles obtained from crime scenes. These
databases can be searched for matches to samples obtained from crime
scenes and have become a very important tool for the police in obtaining
evidence which may lead to the identification and eventual conviction of
offenders.
are taken and stored in controlled conditions and yield reliable high quality
DNA profiles. Samples collected from crime scenes may be of blood,
semen, hair or skin cells, and while DNA is a remarkably robust molecule,
the conditions before collection are seldom ideal and many samples are
degraded. It is here that one of the strengths of the STR-based DNA profile
system comes into play, as it is possible to amplify the short STR loci by
PCR from samples of relatively poor quality. In fact DNA profiling has been
used to revisit unsolved cases and analysis of forensic samples from over 20
years ago has successfully been used to obtain convictions.
13.6 Obtaining More Information from DNA Profiles
A DNA profile from a sample left at a crime scene is only really useful either
if there is a match to it in one of the DNA databases or if you have a profile
from a suspect against which to compare it. The inclusion of the amylogenin
locus in the standard DNA profile makes it possible to determine the
gender of the donor. However, it would be useful in the investigation of
crime to be able to deduce other physical characteristics such as race, hair
and eye color, height and age. Two services currently offered by the
Forensic Science Service test for red hair and infer ethnicity.
The red-hair test is based on detecting mutations in the MC1R gene
which encodes the melanocortin 1 receptor. MC1R acts as a molecular
switch that affects hair color. The test looks at 12 variants of this gene, eight
of which are associated with red hair. The test based around detecting
these can identify 84% of red heads.
Inference of ethnicity is based on studies showing that the frequency of
the STR alleles, used for genetic profiling, differs between populations.
Humans are thought to have evolved from early hominids living in Africa