Biology Reference
In-Depth Information
1E 20
1E 19
1E
18
No F ST correction
1E 17
F ST 0.01
1E 16
1E
F ST 0.03
15
1E 14
1E 13
1E
12
1E 11
1E 10
1E
09
1E 08
0
50
100
150
200
250
UK Caucasian Individuals
Figure 8.2 The SGM Plus frequencies from 252 UK Caucasians are shown with: no correction;
theta (F ST ) 0.01; and theta (F ST ) 0.03. The impact of the theta correction varies - the greatest
effect is with rare alleles and homozygous loci
inbreeding may have occurred. The impact of different theta (F ST ) values can be
seen in Figure 8.2: as the theta increases the profile frequencies decrease.
Profile ceiling principle
In some countries, such as the UK, the approach has been to use a match probability
of 1 in a billion (1 000 000 000). This approach is highly conservative [30]. It does
have the advantage that individual profile frequencies do not have to be calculated
because the value used is much lower than the most common profile frequency, even
if conservative corrections are incorporated [32].
Which population frequency database should be used?
In some cases, the ethnic origins of material recovered from the crime scene are
known: for example, if a woman has been sexually assaulted she can normally
describe the assailant as white, black, Asian, and so on. In such a case, for example if
the assailant was described as white, then it would be logical to use a white Caucasian
allele frequency database to calculate the profile frequency. In other contexts, there
may be no information about who could have left the material at the crime scene. In
countries or regions having substantial populations with different ethnic backgrounds,
a common practice is for the profile frequency to be calculated using an allele
database for each major population group, and to use the most conservative profile
frequency. If we take the example from Table 8.1, the allele frequency data used
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