Question

If there is complete linkage with genes Ss (for smooth or wrinkled seeds) and Gg (for green or yellow seeds), what phenotypes would you expect in the offspring of a cross with one heterozygous parent (Ss, Gg), which would all produce all smooth and green seeds, and a homozygous recessive parent (ss, gg), which would produce all wrinkled yellow seeds?

Answer 1

Answer:

Smooth and green seeds

Smooth and yellow seeds

Wrinkled and green seeds

Wrinkled and yellow seeds

Explanation:

This is a typical dihybrid cross involving two linked genes; one gene coding for seed texture and the other for seed colour. The allele for Smooth seed (S) is dominant over the allele for Wrinkled seed (s) in the first gene while the allele for green seed (G) is dominant over the allele for yellow seed (g) in the second gene.

The cross is between a heterozygous smooth, green plant and a homozygous recessive wrinkled, yellow plant

According to the law of independent assortment, each parent will undergo meiosis to produce the following gamtes with genotypes:

SsGg: SG, Sg, sG, sg

ssgg: sg, sg, sg, sg

Using a punnet square to perform a cross between these gametes ( check attached image), a total of 16 offsprings with four different phenotypes will be expected. The phenotypes are as follows:

SsGg: Smooth and green offsprings (4)

Ssgg: Smooth and yellow offsprings (4)

ssGg: Wrinkled and green offsprings (4)

ssgg: wrinkled and yellow offsprings (4)