In garden peas, yellow (Y) seed color is dominant to green (y). Because yellow and green are two different forms of the same gene (seed color), they are alleles. Use a Punnett square to show a cross between two heterozygous pea plants. What are the phenotype(s) of the offspring? What are the genotype(s) of the offspring?

During a cross, parents produce gametes that combine to form the offspring. In a Punnett Square we write down the gametes produced by the parents and the possible offspring that arises from their combination.

The Y allele (yellow color) is dominant over y (green color).

The cross between two heterozygous plants would be Yy x Yy. During meiosis the alleles separate to the daughter cells, so the gametes will have either the Y allele or the y allele.

The genotype of an individual is the combination of alleles it has for a particular gene.

The genotypes of the offspring are:

1/4 YY
2/4 Yy
1/4 yy

The phenotype of an individual is the manifestation of the trait in the individual which can be observed. It could be seed color, plant height, flower color, etc.

The phenotypes of the offspring are:

3/4 yellow seeds (1/4 YY + 2/4 Yy)
1/4 green seeds (1/4 yy)