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.
