Question

1. For this problem, we’re going to be dealing with the B and Q genes, both of which are located on chromosome 6. Use these letters when providing the genotypes and use typical conventions from class to report your answers to be eligible for credit.

a) You’re going to be performing a dihybrid testcross; tell me what the genotypes are for each of the parents involved in this cross.

b) Cool. List here the four different genotypic classes you’d see in the offspring of this dihybrid testcross. I’ll tell you the first one, since I’m going to put it in the next question.

genotypic class #1: b⁺/b q/q

genotypic class #2:

genotypic class #3:

genotypic class #4:

c) OK, OK. So, b⁺/b q/q is one of the parental offspring genotypes. So what must be the other parental offspring genotype?

Answer 1

a) dihybrid test cross is the cross between an individual who is heterozygous at both loci and homozygous recessive individual.

the genotype of individuals are b+bq+q ( dihybrid) bbqq ( homozygous recessive)

b+bq+q * bbqq

b) b+bq+q * bbqq

	b+q+	b+q	bq+	bq
bq	b+q+/bq	b+q/bq	bq+/bq	bq/bq

c)  b⁺/b q/q is parental type progeny.

there four genotypic classes in the progeny two are parental type and 2 are recombinant type.

parental type progenies are formed from parental type gametes, parental type gametes have same combination of alleles as that in the chromosomes in the dihybrid parent,.

given b+q/bq is parental type.

so one chromosome in the dihybrid parent has b+ and q alleles and the other chromosome in the dihybrid parent is b q+, so another parental type gamete is b q+.

so the other parental type offspring is b q+/b q ( or we can write b/b q+/q).