The genetic linkage among 3 gene loci in guinea pigs is being studied. The loci
ID: 227179 • Letter: T
Question
The genetic linkage among 3 gene loci in guinea pigs is being studied. The loci are part of autosomal chromosomes and they MIGHT be on the same pair of homologous chromosomes. There are two alleles at each locus. At the coat color locus, allele B is for black; and b is for white. At the weight locus, allele H is for fat, and h is for thin. At the tail locus, allele T is for long, and J is for short. Upper case alleles are completely dominant to their respective lower case allele. There are no interactions among the 3 loci. A male guinea pig with the phenotype black, fat and long-tailed was mated with a female guinea pig that was white, thin and short-tailed. Several mattings produced 800 progeny as described in the table: a. What are the genotypes of the likely parental types of gametes produced by the male? b. What locus is in the middle on the genetic map for these loci? c. Calculate the recombination frequency between the coat color and the tail locus. Show your calculations. d. Calculate the recombination frequency between the tail locus and the weight locus. Show your calculations. e. Calculate the recombination frequency between the coat color and the weight locus. Show your calculations. f. What is the expected frequency of double crossovers? Show your calculation. g. What is the estimate of interference for these data? Show your calculation. h. If the 3 loci were segregating independently of each other, how many guinea pigs in the progeny would be expected in the genotypic class, "BbhhTt?Explanation / Answer
a: Since the progeny shows maximum number of progeny with "black, fat and long tail" and "white, thin and short tail", the parental types of gamete produced by male has the genotype of "BHT".
b: When two genes are present close to each other, they show minimum or no crossover.
Crossover frequency between coat color and weight locus(X)= (63+58+55+56/800)x100= 29%
Crossover frequency between coat color and tail locus (Y)= (15+13+58+56/800)x100= 17.75%
Crossover frequency between weight and tail locus (Z)= (63+15+13+55/800)x100= 18.25%
Since Z=X-Y; the tail locus is present in between and the coat color and weight loci are present at two extremes.
c:
Crossover frequency (recombination frequency) between coat color and tail locus (Y)= (15+13+58+56/800)x100= 17.75%
d:
Crossover frequency (recombination frequency) between coat color and weight locus(X)= (63+58+55+56/800)x100= 29%
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