Question

In humans, polydactyly (an extra finger on each hand or toe on each foot) is due to a dominant gene. When

one parent is polydactylous, but heterozygous, and the other parent is normal, what are the genotypic and
phenotypic ratios of their children?

Answer 1

50/50 for both or 2:2

Answer 2

Answer: The genotype ratio of their children is 2Ff : 2 ff

The phenotype ratio is 2 polydactyl individuals : 2 normal individuals.

Explanation: Let F represent the gene for extra finger while f represent the gene for normal finger. From the information provided, F is dominant while f is recessive. A heterozygous parent will have a genotype of Ff while a normal parent will have a genotype of ff. A cross between them will produce 2 Ff and 2 ff. Ff will manifest phenotypically as polydactyl because F is a dominant allele while ff will manifest phenotypically as normal fingers because f is recessive. For a recessive allele to express itself outwardly, it must occur in a homozygous state. Ff is heterozygous polydactyl.

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