The direction of shell coiling in the snail Lymnea is determ

The direction of shell coiling in the snail Lymnea is determined by a maternal effect gene for which the dextral allele is dominant to the sinistral allele. In a cross in which the phenotype of the snail contributing eggs was sinistral, all F_1 progeny are dextral. a) What was the genotype of the snail that contributed eggs? b) These dextral F_1 progeny are self-fertilized and they produce an F_2 generation comprising 50% dextral and 50% sinistral snails. What was the genotype of the sperm donor in the initial Cross? (Don\'t forget to show your work here)

Solution

Answer:

Based on the given information:

dextral allele is dominant to sinistral allele

Phenotype of the snail contributing eggs was sinistral all F1 progeny are dextral
Let Dextral (D) and Sinistral (d)

a) Genotype of the snail that contributed eggs: Dd

In this case egg (Dd) x Sperm (dd) --> F1 (Dd, dd) - F1 progeny is dextral

b) Dextral F1 progeny are self fertilized and produce a F2 generation comprising 50% dextral and 50% sinistral snails.

Genotype of the sperm donor in the initial cross? dd

Explanation: Progeny are self fertilized Dd x dd = Dd, Dd, dd, dd - 50% are dextral and 50% sinistral snails