Question

figure 1. rock color and coat color at three sites on a lava flow (west, mid, and east), and three nearby sites: o’neill hills (o’neill), the tule mountains (tule), and christmas pass (xmas)
in the arizona populations, the melanocortin-1 receptor (mc1r) gene is responsible for coat color phenotype (light or dark). the mc1r d allele, which results in a dark coat, is dominant to the d allele. researchers collected samples of mice from all six study sites and sequenced the mc1r gene. they also collected mice with dark coats from a location in new mexico, the carrizozo lava flow, to determine if the mc1r gene was also responsible for the dark coat colors observed in that population. the rock pocket mouse population in carrizozo is isolated from the populations in arizona. table 1 presents the genotypic data from sampled mice from all seven locations.
table 1. mc1r genotypes of rock pocket mice at seven collection sites

state	collection site	mc1r genotype
arizona	christmas pass	0	0	6

which of the following best explains why the population is not in hardy-weinberg equilibrium?
a) the presence of heterozygotes for the mc1r gene in the east lava flow population indicates that mating is occurring randomly between mice with different coat colors.
b) the selective pressures on the east lava flow population are not strong enough to maintain hardy-weinberg equilibrium.
c) the east lava flow population does not experience migration, which is a required condition for hardy-weinberg equilibrium.
d) the presence of mc1r alleles in the east lava flow population is an indication of gene flow from mice populations living on light granite rocks.

Explanation:

To determine why the population is not in Hardy - Weinberg equilibrium, we analyze each option:

• Option A: Random mating is a condition for Hardy - Weinberg equilibrium. If mating is random (as indicated by heterozygotes), this would support the population being in equilibrium, not explain why it's not. So A is incorrect.
• Option B: Hardy - Weinberg equilibrium can be maintained with or without strong selective pressures. The strength of selective pressures is not the main reason for deviation from the equilibrium in this context. So B is incorrect.
• Option C: One of the conditions for Hardy - Weinberg equilibrium is no migration (gene flow). If the East lava flow population does not experience migration, this would be a condition that supports equilibrium, not explain the deviation. So C is incorrect.
• Option D: The presence of new alleles (from gene flow) violates the Hardy - Weinberg condition of no gene flow. If there is gene flow from mice populations on light granite rocks (introducing new alleles), this would cause the population to deviate from Hardy - Weinberg equilibrium.

Answer:

D. The presence of \( MC1R \) alleles in the East lava flow population is an indication of gene flow from mice populations living on light granite rocks.