Question

Hitchhiker's thumb is inherited via two recessive alleles and causes a hyperextensibility of the thumb. The dominant allele causes a straight thumb phenotype. Predict the phenotypic and genotypic ratios from the following cross.

One parent with Hitchhiker's thumb crossed with a Straight thumbed individual who had a parent with Hitchhiker's thumb.

a. Phenotypic and Genotypic 1:1
b. Phenotypic 2:1 and Genotypic 1:1
c. Phenotypic 1:1 and Genotypic 2:1
d. Phenotypic and Genotypic 3:1

Answer 1

a. Phenotypic and Genotypic 1:1

Step-by-step explanation:

Two recessive alleles are required in order to be phenotypically affected for Hitchhiker's thumb. Hence, the genotype of the parent with Hitchhiker's thumb would be homozygous recessive.

Assuming the trait to be represented by the allele h, the genotype of the parent with Hitchhiker's thumb would be hh while the genotype of an individual with straight thumb who had a parent with Hitchhiker's thumb would be heterozygous, Hh.

Crossing the two individuals.

hh x Hh

Progeny: Hh hh Hh hh

Hh - Straight thumb

hh - Hitchhiker's thumb

Hence, the genotypic ratio is 1:1 while the phenotypic ratio is also 1:1.

The correct option is a.