Red-Green colorblindness is a X-linked recessive disorder. Huntington\'s is an a

Question

Red-Green colorblindness is a X-linked recessive disorder. Huntington's is an autosomal dominant disorder. Susan's father is color blind and has Huntington's disease and is heterozygous for the Huntington's allele. Her mother is normal and has no history of colorblindness or Huntington's in her family. Her brother has developed Huntington's but is not colorblind. Her husband Greg is healthy and has no incidence of either disorder in his family. Susan is not colorblind and has not yet be tested to see if she has inherited the Huntington's allele. What is the chance that a child of Susan and Greg will be a girl with normal vision but having Huntington's? a. 1/8 b. 1/16 c. 1/32 d. 1/64 e. 1/4

Explanation / Answer

We first need to know what susan's genotypes are:

since her father had huntington's and color blindess and mother did not have any, the crosses would be :

and

this explains that susan is a carrier for color blindness XCXc and could be a carrier for huntington's as well

chances of susan being a carrier for huntington's is 50% or 1/2

since her husband does not have an family history of both the diseases, we will assume he is not a carrier for both, since we have to find out the chances of them having a girl child with normal vision and having huntington's , we would assume susan is a carrier. the crosses would be as follows:

and

chances of having a girl are 1/2 chances of girl having normal vision are 1/2 and chances of having huntington's is 1/2 as well . here we can also take into account the chances of Susan having huntington's is 1/2 as well

therefore, it would be - 1/2 x 1/2 x 1/2 x 1/2 = 1/16

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