Name: ______________________________________

calicoPractice Problems – Sex Linkage

1. Coat color in cats is a codominant trait and is also located on the X chromosome. Cats can be black, orange or calico. A calico cat has black and orange splotches. In order to be calico. the cat must have an allele for the black color and an allele for the orange color. Use a punnett square to show why there are no male calico cats.

 

 

2. A female calico cat is crossed with a male black cat. What are the phenotypes of the offspring and in what proportion?

 

 

3. Also located on the X chromosome of a cat is a gene that codes for deafness. This gene is recessive. A black female cat that is heterozygous for deafness (Dd) is crossed with a orange male cat that is not deaf. Show the cross. What are the phenotypes of the offspring and in what proportion? Hint: place two letters on the X chromosome in your cross.   (You will need to use two superscript letters on your X chromosome)

 

 

4.  Eye color in fruit flies is sex linked, with the recessive allele causing white eyes.  Show the cross for a white eyed female and a red-eyed male.   How many offspring will have white eyes and what is their sex?

 

 

 

5.  In humans, colorblindness is sex linked and recessive.  If a woman is a carrier for the trait, what is the chance that her sons will be colorblind?   Her daughters?   (Assume the father has normal vision.)

 

 

 

6.  In humans, hemophilia is sex linked.    If a woman is a carrier for the trait, what is the chance that her daughters will also be carriers.  (assume father is normal)

 

 

rooster

7. It is difficult to determine the sex of very young chickens, but it is easy to tell, by visual observation, whether the feathers are "barred." The barred pattern is inherited as a sex-linked dominant trait. This trait is used regularly by chicken breeders who receive orders for only male or female chicks, and must be able to deliver the appropriate sex of very young birds. Determine whether the male and female parents should be taken from normal or barred true-breeding lines in order for the sex of all chicks to be determined at the time of hatching. Show the Punnett square for the mating you select, to confirm that the desired phenotypes result.

(Note: In birds, sex is determined as follows: XX = male, XO = female; only the X chromosome carries sex-linked genes.)