Question

Achondroplasia is caused by a dominant allele. Two parents have achondroplasia, but their child does not. Explain how it is possible for the child not to have achondroplasia.

Answer 1

When both parents have achondroplasia, the chance for them, together, to have a child with normal stature is 25 percent. Their chance of having a child with achondroplasia is 50 percent. Their chance for having a child who inherits the gene mutation from both parents (called homozygous achondroplasia - a condition that leads to death) is 25 percent.