Acho ndroplasia is an autosomal dominant form of dwarfism. People with acho ndroplasia are heterozygotes because carrying two copies of the dominant, mutant allele is fatal during embryogenesis. Two people with acho ndroplasia decide to start a family.

Two people with acho ndroplasia will have 50% of chance to have a child with acho ndroplasia. According to Mendelian inheritance, we can indicate dominant allele by A and recessive allele by a, so dominant homozygotes are AA, recessive homozygotes aa and heterozygotes Aa.

Two heterozygotes Aa will have 50% of chances to have a child with acho ndroplasia (AA), 25% of chances to have a recessive homozygote child (aa) and 25% of chance to concieve a child with two dominant mutant allele (AA):

Parental generation: Aa x Aa

F1 generation: AA, Aa, Aa, aa

Ratio: 1 : 2 : 1