Video Transcript
A cross between two rabbits
produced offspring with the genotype uppercase B uppercase B uppercase F lowercase f
only. The genotype of the father was
uppercase B uppercase B uppercase F uppercase F. What was the genotype of the
mother?
All offspring inherit genetic
material in the form of DNA from their biological parents. In this question, we are discussing
the inheritance of two genes in particular: gene B and gene F. Because we are looking at the
inheritance of two genes and their respective alleles, we know this question is
about dihybrid inheritance. To help us answer this question,
let’s use a Punnett square to show a dihybrid cross.
We are given the genotype of the
father in the question. And to complete the Punnett square,
we need to determine the combination of alleles that would be present in his
gametes. Each gamete will contain only one
allele for each gene. As this father is homozygous
dominant, all of his gametes will have the combination uppercase B uppercase F. Let’s put the alleles found in the
father’s gametes along the top of our Punnett square.
We are also told in the question
that all of the offspring had the same genotype: uppercase B uppercase B uppercase F
lowercase f. So, we can complete the cells of
our Punnett square with this information. Now, we are looking for the
mother’s genotype, which we can determine by figuring out the combination of alleles
present in her gametes. In each of the offspring genotypes,
one uppercase B and one uppercase F must have come from the father. So, the other uppercase B and the
lowercase f must have come from the mother.
As all the possible genotypes of
the offspring are the same, this must have been the only combination of alleles
present in the mother’s gametes. So, the mother’s gametes all
contained the alleles uppercase B and lowercase f. We know that we need two alleles
for each gene present in the mother’s genotype. Working backwards, we can conclude
that because all of the possible combinations of alleles in the gametes were the
same, her genotype must have been uppercase B uppercase B lowercase f lowercase
f.
So, we have our final answer. The genotype of the mother must
have been uppercase B uppercase B lowercase f lowercase f.
