## Problem box answer

Using the allele frequencies in Table 2.3 we can calculate the expected genotype frequencies for each locus:

D3S1358: 2(0.2118)(0.1626) = 0.0689; D21S11: 2(0.1811)(0.2321) = 0.0841; D18S51: (0.0918)2 = 0.0084; vWA: (0.2628)2 = 0.0691; FGA: 2(0.1378)(0.0689) = 0.0190; D8S1179: 2(0.3393)(0.2015) = 0.1367; D5S818: 2(0.3538)(0.1462) = 0.0992; D13S317: 2(0.0765)(0.3087) = 0.0472; D7S820: 2(0.2020)(0.1404) = 0.0567.

As is evident from the allele designations, the amelogenin locus resides on the sex chromosomes and can be used to distinguish chromosomal males and females. It is a reasonable approximation to say that half of the population is male and assign a frequency of 0.5 to the amelogenin genotype. The expected frequency of the ten-locus genotype is therefore 0.0689 x 0.0841 x 0.0084 x 0.0691 x 0.0190 x 0.1367 x 0.0992 x 0.0472 x 0.0567 x 0.5 = 1.160 x 10-12. The odds ratio is one in 862,379,847,814. This 10-locus DNA profile is effectively a unique identifier since the current human population is approximately 6.5 billion and we would expect to observe this exact 10-locus genotype only once in a population 132 times larger than the current human population. In fact, it is likely that this 10-locus genotype has only occurred once in all of the humans who have ever lived.

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