What kind of cross would help identify if a yellow-seeded pea plant is homozygous or heterozygous?

To determine whether a yellow-seeded pea plant is homozygous (YY) or heterozygous (Yy), a test cross with a plant that has a known recessive phenotype for seed color is the most effective approach. In this case, the recessive phenotype would be the green-seeded trait, represented by the genotype yy.

When performing a test cross with a homozygous recessive plant, if the yellow-seeded plant is homozygous (YY), all offspring will express the yellow phenotype, as they will all inherit one dominant Y allele from the yellow-seeded parent and one recessive y allele from the green-seeded parent. In contrast, if the yellow-seeded plant is heterozygous (Yy), the offspring will show a 1:1 ratio of yellow to green seeds, reflecting the presence of both yellow and green offspring.

This contrast in potential offspring phenotypes enables the determination of the yellow-seeded plant's genotype. A self-cross or crossing with another yellow-seeded plant would not give any clarity about the homozygosity or heterozygosity, as both could yield only yellow-seeded offspring regardless of the genotype of the yellow plants involved.