A forensic analyst evaluates a single autosomal STR locus in a crime scene sample, revealing a heterozygous genotype with alleles 14 and 15. The population frequencies of alleles 14 and 15 are 0.1 and 0.3, respectively. Assuming Hardy-Weinberg equilibrium, what is the probability that a randomly selected unrelated individual would match this heterozygous genotype at this locus?
- A 0.01
- B 0.03
- C 0.06 ✓
- D 0.09
Correct answer: C. 0.06
Explanation
For a heterozygous genotype, the random match probability is calculated using the formula 2pq, where p and q are the population frequencies of the two alleles. Here, p equals 0.1 and q equals 0.3, so 2 times 0.1 times 0.3 equals 0.06. Option B represents pq alone, which is a common error where the analyst forgets to multiply by two, as either allele can be contributed by either parent. Option A is p squared.
Reference: Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers, 2nd ed.
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