Question

People with achondroplastic dwarfism are heterozygous for a dominant allele conferring this trait. The homozygous dominant condition for the achondroplasia allele is lethal. What is the probability that two people with achondroplastic dwarfism will have a surviving child with this trait?

Answer 1

When both a man and woman carry a lethal allele for the same gene each pregnancy has 25 % chance of  aborting

Answer 2

Two people with achondroplastic dwarfism will have 50% of their surviving child having heterozygous trait for achondroplastic dwarfism. 25% of child will have homozygous lethal dominant allele for the achondroplasia and 25% child will have homozygous recessive allele.