Question

At the C locus in horses, chestnuts (sorrels) are CC, palominos are Cc^cr, and cremellos are c^cr c^cr. Assume we have two large populations of horses in which stallions of one herd are bred to mares of the other herd, and vice versa. Coat color is not a factor in selection and/or mating decisions. The frequency of the C allele in population 1 is 0.70, while the frequency of the C allele in population 2 is 0.25.

a. What will be the gene and genotypic frequencies at the C locus in the offspring (F1) population?

b. If the F1 offspring are mated among themselves, what will be the gene and genotypic frequencies in the F2 generation (assuming HW equilibrium)?

Answer 1

a)

In Population 1:

Frequency of C allele = p₁ = 0.7
Thus, frequency of ccr allele = q₁ = 0.3

In Population 2:

Frequency of C allele = p₂ = 0.25
Thus, frequency of ccr allele = q₂ = 0.75

Now, if the Stallions from one herd are bred to the Mares of the other herd and vice versa, populations are effectively mixed.

This means that the allele frequencies will be an average of the two, assuming an equal number of Stallions and Mares are taken from either population, that is if x Stallions from Population 1 are bred with Mares from Population 2, then x Mares from Population 1 would be bred with Stallions from Population 2.

Thus, New allele frequencies will be:

Frequency of the C allele = p = (0.7 + 0.25) / 2 = 0.475
Frequency of the ccr allele = q = (0.3 + 0.75) / 2 = 0.525

The Genotypic Frequencies are:

CC = q² = (0.475)² = 0.2256
Cccr = 2pq = 2 * 0.475 * 0.525 = 0.4988
ccr ccr = q² = (0.525)² = 0.2756

b.

Since Hardy-Weinberg equilibrium is maintained, the frequencies remain unchanged between the F1 and F2. This is because mating is random and no selection is present.