Biology Reference
In-Depth Information
comparing VNTR profiles was a major limitation. STR profiles can be digitized very
easily to create a digital code. This digital code allowed for the effective computer-
ization of DNA profiles (see Chapter 6).
The UK NDNAD was established using the SGM multiplex, which analysed six
STR loci and the amelogenin locus. The average match probability of SGM was
1in10
8
of the population, which for a population of 58 million within the UK
was deemed acceptable. However, when six loci were used there were a number of
coincidental (adventitious) matches.
Adventitious hits
In 1995 Raymond Easton was asked to donate a DNA profile as part of an
investigation into a domestic dispute. Four years later a burglary at a home
approximately 200 km from where Raymond Easton lived generated a DNA
profile that was compared with the NDNAD. This profile matched that of Ray-
mond Easton and he was accused of the crime. A match probability of 1 in
37 million was reported. At the time of the burglary, Raymond Easton was suf-
fering from Parkinson's disease and was unable to walk more than 10 m unaided.
This was an example of an adventitious hit. The test was conducted using the
six SGM loci, but the chance that a similar adventitious cold hit will occur has
been reduced greatly by extending the test to 10 loci [7].
In 1999, the six-locus SGM test was changed to the 10-locus SGM Plus
test.
The chance that two DNA profiles from unrelated people will match at all 10 loci
is less than 1 in 1 billion. To date no two people have been found to match at all
10 loci; however, matches to two or more people do occur if a partial DNA profile,
recovered from poor-quality DNA, is searched against the NDNAD.
Operation of the NDNAD
The NDNAD has two main sets of data: profiles generated from evidence that
has been collected from crime scenes (350 000 were retained in the database as of
31 March 2010) and profiles generated from individuals (4.85 million as of 31 March
2010 [8]).
A biological sample collected from a crime scene will be submitted for DNA
analysis. The resulting DNA profile will be compared with those currently held on
the NDNAD and if there is a match then this will be reported back to the police
force that collected the sample (Figure 10.1).
Since 2000, on average the NDNAD has provided around 40 000 crime scene
to individual matches each year (Figure 10.2). Although the intention had been to
use the NDNAD to match samples from serious crimes such as sexual assaults and
