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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. In humans, Duchenne muscular dystrophy (DMD)  is a disease where muscles become weaker over time.  The gene is located on the X chromosome and is recessive.   Those afflicted with this disease usually die in childhood.   If a female is a carrier for DMD, what percentage of her sons will inherit the disease?  What percentage of her daughters will inherit the disease.

 

 

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. Show a reciprocal cross: a red eyed female (homozygous) and a white eyed male.

 

 

 

6.  In humans, colorblindness is sex linked and recessive.  If a woman is is colorblind, what percentage of her sons will also be colorblind?