Thomas Hunt Morgan studied Drosophila melanogaster, better known as fruit flies. He noticed that one of
his male fruit flies had white eyes (fruit flies normally have red eyes). He wanted to understand how the
white-eyed trait would be passed on to the next generation.
1. He started by crossing the white-eyed male with a homozygous red-eyed female. If red eyes are
dominant to white eyes, what phenotypes would you expect to see in the F1 generation?
2. Morgan then crossed two members of the F1 generation. What genotypes and phenotypes would
you expect to see in the F2 generation?
3. Morgan saw that in the F2 generation, no females had white eyes. ½ of the males in the F2
generation had red eyes while the other half had white eyes. Morgan realized that the gene for eye
color was located on the X chromosome. While the white-eyed gene was recessive, males
expressed it with only one copy because they only had one copy of the gene.
Repeat the cross of two F1 individuals, this time keeping in mind that eye-color is sex-linked.
4. As you watch the video, check your work for the first three problems.
You are a cat breeder. Your customers tell you what color kitten they want and it is your job to fill
their order. Orange coat color (XO) is a sex-linked trait. Heterozygous females will have patches of
orange fur (known as calico) while homozygous orange females will have all orange fur. The other sexlinked fur allele is simply Xo for not orange.
Work in groups to fill the following customer orders. When the customers arrive, you will have to explain
to them verbally (raise your hand and explain to Mr. B when you have finished all problems) how you
decided which color parent cats to breed. Use Punnett squares to show your work. Your goal is to choose
parent cats that will have the greatest chance of producing the desired kitten.
1. An orange female kitten
2. A calico female kitten
3. An orange male kitten
4. A calico male kitten
Challenge: try to find more than one pair of parents that would produce the desired kitten