Question

Huntington's disease is an inherited condition in which the neurons in the brain break down over time. An individual who inherits one allele for Huntington's disease will most likely express the symptoms. A man who is heterozygous for the Huntington's disease allele has a child with a woman with no family history of Huntington's disease.
Which of the following best explains the percent chance that the child will inherit an allele for Huntington's disease?
There is a 100% chance that the child will inherit the Huntington's disease allele, because the father has the condition.
There is a 50% chance that the child will inherit the Huntington's disease allele, because the father has one copy of the allele.
There is a 25% chance that the child will inherit the Huntington's disease allele, because the allele comprises 25% of all alleles for the gene in the parents.
There is a 0% chance that the child will inherit the Huntington's disease allele, because the mother has no family history of the condition.

Answer 1

There is a 50% chance, because Huntington's is autosomal dominant and the heterozygous father (Hh) will pass either the H (disease) allele or the h (normal) allele with equal probability. Crossing Hh × hh gives 50% Hh (affected) and 50% hh (unaffected).