Theresa has huntingtons disease while her husband louis does not what percentage of their children will develop this disease

Question

Theresa has huntingtons disease while her husband louis does not what percentage of their children will develop this disease

Answer 1

Hi Anya,

Huntington's disease is an autosomal dominant trait, so to have Huntington's, the affected only needs one dominant allele. That means to be unaffected you need to recessive alleles therefore Theresa is not a carrier. To represent the possibilities, let's use 'H' to represent the dominant allele and 'h' to represent the recessive. If one of their children has a single 'H' they will have the disease. We should do a Punnett square-

In possibility one, Theresa is homozygous for Huntington's (HH, y axis) and Louis is homozygous recessive (hh, x-axis).

h. h

H Hh. Hh

H. Hh. Hh

In this scenario, all of their children would be affected since they all have a dominant allele (H).

In possibility two, Theresa is heterozygous for Huntington's (Hh) because remember to be affected, which the question states she is, you only need one dominant allele. Louis is unaffected so he will remain homozygous recessive (hh).

h. h

H. Hh. Hh

h. hh. hh

So if they were to have four kids, theoretically based on the square, two of them would be affected and two of them would not be. So what % is 2/4?