Question

You observe that the frequency of an allele at the YAPPY gene appears to be at a stable equilibrium (p* = 0.5) in a finite but extremely large population not experiencing mutation. You note that the heterozygotes for this gene tend to have more offspring because they survive to a greater degree than either homozygous genotype. Which of the following term best describes what is happening?

	A.	Mutational equilibrium
	B.	Hardy-Weinberg Equilibrium
	C.	Wright-Fisher population
	D.	Underdominance
	E.	Overdominance

You observe that the frequency of an advantageous allele decreases from one generation to the next by 20%. Which of the following is the most likely explanation?

Natural selection is driving the advantageous allele to fixation in an extremely large population.
	B.	Natural selection is driving the advantageous allele to be lost in an extremely large population.
	C.	Natural selection is driving the advantageous allele to fixation in a small population.
	D.	Natural selection is driving the advantageous allele to be lost in a small population.

Answer 1

1. Overdominance

Overdominance is the condition wherein a heterozygote produces a phenotype more extreme or better adapted than that of the homozygote.

Underdominance is the selection against the heterozygote, causing disruptive selection and divergent genotypes.

2. Natural selection is driving the advantageous allele to be lost in a small population.

smaller populations are more likely to be affected by chance events since there are not as many alleles to “balance out” random changes in allele frequencies. The phenomenon is called as genetic drift.