Practice Problems – Sex Linkage

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1. Coat color in cats is a codominant trait and is also located on the X chromosome. Cats can be black, orange or tortoiseshell (mix of black and orange) 

 A tortoiseshell cat has black and oRange fur color (XBXR).   Show the cross between a female tortoiseshell cat and an orange male ( XRY) .   How many offspring are calico?


2. A black female cat is crossed with an orange male 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. Ared 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?


7. If a man is colorblind, what percentage of his sons will be colorblind (assuming the mother is not a carrioer)?


8.A colorblind woman who is also a carrier for sickle cell anemia (Aa) is married to a normal vision man who is also a carrier for sickle cell anemia. What isthe probability that their SONS will be colorblind and have sickle cell disease.