Question

Huntington’s disease is inherited in an autosomal dominant pattern. What was the probability of children #1 and #2 inheriting the disorder, and did child #3 have a chance to get Huntington’s disease?

Answer 1

Answer: C. child #1 and #2 each had a 50% chance of getting HD; child #3 had a 0% chance.

Huntington’s disease is inherited in an autosomal dominant pattern which means you only need one allele from any parents to get the disease. That also means that there is no carrier, a healthy person must not carry any of the genes. 

Parent of child 1 and 2 is a healthy male and female with HD. If the female has 2 HD gene, all of her children will get HD. But since she has a few normal children, then she must be heterozygous. Child of one heterozygous parent has 50% to get HD. 

Since child 1 is normal, there is no chance for child 3 to get HD.