A large population of fish live in a lake. The color of their scales is determined by two different alleles of the S gene, S1 and S2. Homozygous S1 fish have yellow scales, S2 homozygotes have blue scales, and heterozygotes are green. Scientists catch 100 fish at random and record their color. Among those 100 fish are 30 yellow, 50 blue, and 20 green ones.

After the original sample is analyzed, an asteroid landed in the lake and killed all the fish that happened to be in one location. When 100 fish were sampled again, 15 were yellow, 75 were blue, and 10 were green.

-What is the frequency of the S¹ allele in the population before the asteroid hit?

Question

Quizplus · Accepted Answer

Before the asteroid hit, the population consisted of 30 yellow (SS), 50 blue (ss), and 20 green (Ss) fish. The frequency of the S allele can be calculated by taking the total number of S alleles and dividing it by the total number of alleles. Each yellow fish has two S alleles, and each green fish has one S allele. Therefore, the total number of S alleles is (2*30) + (1*20) = 60 + 20 = 80. The total number of alleles in the population is 2*100 (since each fish has two alleles) = 200. Thus, the frequency of the S allele is 80/200 = 0.40.

A Large Population of Fish Live in a Lake