An STR locus on chromosome 6 has multiple alleles, each with a different number

Question

An STR locus on chromosome 6 has multiple alleles, each with a different number of CA repeats (the allele name is the number of tandem CA repeats). In the American population, the alleles have the following frequencies: Allele Frequency 20 0.100 21 0.001 22 0.120 23 0.050 24 0.300 25 0.100 26 0.009 27 0.090 29 0.230 These allele frequencies describe the entire American gene pool for the STR locus (the sum of these frequencies = 1.000). Assume that the population is in Hardy-Weinberg Equilibrium.

a. What’s the expected frequency of 25/25 homozygotes?

b. What genotype (not allele) is expected to be the most common in this population?

c. What’s the expected heterozygosity at this locus? (Hint: the heterozygosity can be calculated as 1 minus the sum of the frequencies of all the homozygotes.)

Explanation / Answer

p2 + 2pq + q2 = 1 and p + q = 1

p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals

a)Ans: 1

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