USA Biology Olympiad (USABO) Practice Exam

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What is the frequency of the a allele in a population of 15 AA, 25 Aa, and 10 aa individuals?

0.25
0.35
0.45
0.55

The correct answer is: 0.45

To determine the frequency of the a allele in the given population, one must first calculate the total number of alleles present and then the number of a alleles. The population consists of: - 15 AA individuals, each contributing 2 A alleles. - 25 Aa individuals, each contributing 1 A allele and 1 a allele. - 10 aa individuals, each contributing 2 a alleles. First, calculate the total number of each allele: - Total A alleles from AA individuals: 15 AA * 2 = 30 A alleles. - Total A alleles from Aa individuals: 25 Aa * 1 = 25 A alleles. - Total a alleles from Aa individuals: 25 Aa * 1 = 25 a alleles. - Total a alleles from aa individuals: 10 aa * 2 = 20 a alleles. Now, sum these contributions to find the total number of A and a alleles: - Total A alleles = 30 + 25 = 55 A alleles. - Total a alleles = 25 + 20 = 45 a alleles. Given that each individual contributes a total of 2 alleles, the total