Achondroplasia is a common cause of dwarfism in humans. All individuals with achondroplasia are thought to be heterozygous at the locus that controls this trait. When two individuals with achondroplasia mate, the offspring occur in a ratio of 2 achondroplasia : 1 normal. What is the MOST likely explanation for these observations?
A) Achondroplasia is incompletely dominant to the normal condition.
B) Achondroplasia is codominant to the normal condition.
C) The allele that causes achondroplasia is a dominant lethal allele.
D) The allele that causes achondroplasia is a recessive lethal allele.
E) The allele that causes achondroplasia is a late-onset lethal allele.

Question

Quizplus · Accepted Answer

The allele that causes achondroplasia is a recessive lethal allele. This means that individuals who are homozygous for the allele will die before birth. Therefore, the only offspring that can be produced by two individuals with achondroplasia are heterozygous, which have achondroplasia.

Achondroplasia Is a Common Cause of Dwarfism in Humans