双杂交组合

In pea plants Gregor Mendel also performed dihybrid crosses, breeding experiments between organisms that vary by two traits, like seed shape and seed color.

For example, if one parent is homozygous dominant for round and yellow seeds and the other is homozygous recessive for wrinkled and green seeds, all plants of the F1 generation area dihybrids, meaning that they're heterozygous for two traits.

The F1 plants display the dominant phenotype for both traits and have round and yellow seeds.

When they self fertilize, their progeny, the F2 generation, includes plants with round, yellow seeds, round green seeds, wrinkled yellow seeds, and wrinkled green seeds, in a nine to three to three to one ratio.

Importantly, the relationship of round to wrinkled seeded plants and yellow to green seeded, is three to one for both, indicating that these traits segregated independently, which demonstrates the principle of independent assortment.