Which of the following populations is not in Hardy-Weinberg equilibrium?
a. a population with 12 homozygous recessive individuals (yy), 8 homozygous dominant individuals (YY), and 4 heterozygous individuals (Yy)
b. a population in which the allele frequencies do not change over time
c. p2 + 2pq + q2 = 1
d. a population undergoing natural selection
The correct answer is d. a population undergoing natural selection.
A population undergoing natural selection is not in Hardy-Weinberg equilibrium because natural selection causes changes in allele frequencies over time. Hardy-Weinberg equilibrium assumes no evolutionary forces (such as natural selection, genetic drift, mutation, migration, or non-random mating) are acting on the population, so the allele frequencies remain constant across generations.