Question

Researchers believe that in a fish species, individuals with the recessive genotype aa are predisposed to disease. Homozygous dominant (AA) individuals and heterozygous (Aa) individuals are not believed to be susceptible to this disease. A pond was stocked with 100 fish of the AA genotype and 100 fish of the aa phenotype, and the fish were allowed to breed. In the next generation, 35 percent of the fish had the dominant (AA) phenotype. What does this result indicate?

Answer 1

Answer:

The homozygous dominant phenotype is higher than expected, indicating that evolution has occurred.

Explanation:

At the start there are 200 fishes in the pond, 100 of them are AA(50%) and 100 of them are aa(50%). Using the Hardy-Weinberg Equilibrium equation we can say that the gene frequency is

A=0.5

a=0.5

With those frequency, the expected percentage of offspring with dominant genotype will be:

AA= 0.5 * 0.5 = 0.25 = 25%

The number of homozygous dominant found is 35% which is higher than expected  (25%). Higher homozygous dominant frequency than expected means the Hardy-Weinberg Equilibrium is changed. In this case, evolution probably the cause that shifts the gene frequency.