Huntington disease is a rare fatal, degenerative neurological disease in which individuals start to show symptoms, on average, in their 40s. it is caused by a dominant allele. joe, a man in his 20s, just learned that his father has huntington disease. a. what is the probability that joe will also develop the disease? b. joe and his new wife have been eager to start a family. what is the probability that their first child will eventually develop the disease?

a. 50% b. 25%

Explanation:

If you have a dominant disease, you will always have it if you have the gen.

Joe's father has it.

If his father was heterozygous dominant, he has two genes for the same trait and could have the other gen recessive.

In this case, you have a 50% chance of joe having the disease.

If his wife did not have the disease, and joe has it, the chances of their child to have it is 25%

To know that, you can draw the possibilities.

Joe's father: Aa (A is the dominant, sick gen)

Joe's mother: aa

Aa x aa = Aa Aa aa aa = 50% having it Aa 50% not having it aa.

Joe's possibilities: Aa or aa

Joe's wife: aa

Possibilities of offspring:

Aa x aa = 50% having it Aa 50% not having it aa.

aa x aa = 100% not having the disease.

Their child has 1/4 posibilities to have it