Question

Huntington's disease, an autosomal dominant disorder, is expressed only with a homozygous phenotype.
a. True
b. False

Answer 1

b. False

Being autosomal "dominant" means that only one copy of the dominant allele need be present to cause the disorder.
So if H is the dominant Huntington allele, and h is normal, HH (homozygous dominant) or Hh (heterozygous) will lead to Huntington. Only homozygous recessive will be free from the disorder, or normal (hh).