Consider two gene loci in horses, locus 1 and locus 2. Each locus is on a differ
ID: 211848 • Letter: C
Question
Consider two gene loci in horses, locus 1 and locus 2. Each locus is on a different, non-homologous autosomal chromosome. Alleles at locus 1 influence coat color. Allele B1 is for black and allele B2 is for pinto. Allele B1 is completely dominant and allele B2 is recessive. Alleles at locus 2 influence tail length; allele T1 is for long and allele T2 is for short. Allele T1 is completely dominant to the recessive allele T2. Horse 1, genotype B1B2 T1T2, mates with horse 2, genotype B1B2 T1T2. Please provide your calculations and rationale for all parts. a. How many different gametes are expected to be produced by horse 2? b. How many different genotypes are possible in the progeny of that mating? c. What is the expected frequency of gametes with genotype B1T2? d. What fraction of the progeny is expected to be true-breeding for black coat color? e. If over the years, 20 progeny are produced, how many are expected to have long tail with black coat color? f. What fraction of the gametes from horse 2 has allele B1? SHOW ALL YOUR CALCULATIONS.
Explanation / Answer
Parental cross: B1B2T1T2 X B1B2T1T2
Number of different gametes produced by each parent = 2 X 2 = 4
Number of genotypes possible = 3^n (n = number of genes)
= 3^2 = 9
Frequency of B1T2 gamete = 1/4 = 0.25 = 25%
Progeny with B1B1 = 4/16 = 1/4 = 0.25 = 25%