Question

The fatal human illness called Huntington disease is caused by a dominant mutant allele. Calculate the probability that a couple will have a child with the disease if the father is heterozygous and the mother is homozygous recessive.

Answer 1

Answer: There is a 50% chance that the offspring will inherit Huntington's disease

Explanation:

Huntington's disease is expressed by a dominant allele.

Since the father is heterozygous for Huntington's disease, his genotype would be as follows:Hh

Even though he carries a normal allele, the dominant allele is disease causing and thus masks the effects of the normal allele, therefore he expresses the disease.

The mother does not have Huntington's because she is homozygous recessive, in other words, she carries 2 copies of the normal alleles.with the genotype hh.

If you do a punnet square, and you cross the mother and father, the following genotypes can be produced:

Hh, Hh, hh, hh

Therefore, there's a 50% chance that the offspring will inherit the disease causing allele and 50% chance that the offspring will not inherit it.