Question

Using punnet square,try to find out the nature of offspring of a test cross what ratio did you get?

Answer 1

Gametes	Y	?
y	Yy (Yellow)	Yy (Yellow)
y	Yy (Yellow)	Yy (Yellow)

Gametes	Y	?
y	Yy (Yellow)	yy (green)
y	Yy (Yellow)	yy (green)

Test cross is used to find the genotype of an individual by crossing with a individual of known phenotype. The resulting offsprings are then observed to find the genotype of parent. The following is the example

Monohybrid test cross: If a yellow pea (Y?-unknown genotype with dominant yellow allele 'Y') is crossed with homozygous green pea (yy-genotype having both recessive alleles y) based on the genotypes of offsprings the genotype of crossed yellow pea can be known.

Punnet square 1: see table 1

Since all off springs are yellow pea and obtained heterozygous genotype, it indicates the parent yellow pea genotype is homozygous YY.

Punnet square 2: see table 2

Since all off springs are in 1:1 ratio of yellow pea and green pea, it indicates the parent yellow pea genotype is heterozygous Yy.