Question

In freshwater snails, pigment color is influenced by two genes. If two heterozygous pigmented freshwater snails were crossed and offspring were produced in a ratio of 9 pigmented snails to 7 albino snails, what are the genotypes of the offspring?
a. (A_B_),(A_bb)(aaB_)(aabb)
b. Genotype of pigmented snail
c. Genotype of Albino Snails

Answer 1

Answer:

The genotype of pigmented snails are A_b_

The genotype of Albino snail are A_bb; aaB_

Explanation:

The parent genotypes and offspring phenotypic ratios in this table can help you figure out what kind of inheritance is at work.

Parent Genotypes Offspring Phenotypic Ratio   Type of Inheritance

Aa x Aa                    3 A_ : 1 aa             Simple dominance, monohybrid cross

Aa x Aa                    1 AA : 2 Aa : 1 aa                           Incomplete dominance

AaBb x AaBb         9 A_B_ : 3 A_bb : 3 aaB_ : 1 aabb            Dihybrid cross

AaBb x AaBb        9 A_B_ : 3 A_bb : 4 aaB_ : aabb             Recessive epistasis

AaBb x AaBb        12 A_B_ : A_bb : 3 aaBb : 1 aabb            Dominant epistasis

Answer 2

Answer:

a. (A_B_),(A_bb)(aaB_)(aabb)

Explanation:

This scenario is an example of recessive epistasis.

It involves two recessive alleles concealing the expression of an allele at varying locus.

The 9:7 ratio seen in this case is a rare form of epistasis known as duplicative recessive epistasis (a situation in which the other gene expression are masked due to the effect of either aa or bb presence on them).

In this scenario, if snails possess two copies of one or the other allele I.e allele a or allele b, pigment production would be inhibited leading to albino individuals.

A recessive phenotype is seen for a homozygous recessive gene at Gene A or Gene B.

Therefore, the genotypes of the offspring is AABB, AaBB, AABb, aaBb, aaBB, AAbb, Aabb and aabb.