A homozygous round yellow seed is crossed with a homozygous

A homozygous round yellow seed is crossed with a homozygous wrinkled green seed.

a. What proportion of the round and yellow F1 progeny from this cross is homozygous at both loci?

b. Assuming Mendelian ratios, what proportion of the round and yellow F2 progeny from this cross is homozygous at least at one locus?

c. Under what conditions would you expect to see only parental phenotypes in the offspring?

Solution

Its given that round and yellow seed (which is homozygous) i crossed with a wrinkled geen seed (which is homozygous).

Therefore this cross can be represented as RRYY X rryy (P1 or first parental generation)

The gamete of P1 are - RY and ry

Hence the F1 generation\'s genotype will be RrYy

(a) There are no homozygous F1 progeny in this cross.

(b) F2 generation cross can be represented as RrYy X RrYy

The punnett square for the cross of F2 is a follows-

Parental combinations of the genotype R-Y- are in the phenotypic ratio 9:16 (yellow and round)

Parental combinations of the genotype rryy are in the phenotypic ratio 1:16 (green and wrinkled)

So, asuming Mendelian ratios, the homozygous F2 progeny are in the ratio 1:8 , which are homozygous at at-least one gene locus.

(C) Only parental genotypes can be obtained in the F3 when all seeds of the F2 having the genotype R-Y- are self pollinated.