Question

What is the probability that in the cross Aa Bb × aa Bb the progeny will be aaBB?

Answer 1

Set up a dihybrid cross.

The idea is that the parent has four different chromosomes. Each of those four chromosomes has on it one copy of each possible allele - that is, one chromosome has the A allele, another has the a allele, a third has the B allele and the last has the b allele.

Any of those individual chromosomes from the parent could end up in the offspring - subject to the constraint that each child will get one chromosome carrying either of the two A or a alleles, and one chromosome carrying either of the two B or b alleles.

So the possible combinations of alleles that the offspring could get from the first parent are AB, Ab, aB or ab.

The possible combinations of alleles the offspring could get from the second parent are aB ab aB and ab.

Set up a Punnett Square with the parents' genotypes at the top and fill it in. What percentage or ratio of the offspring have the genotype aaBB that it asks you about?

Answer 2

Thank you blues!