What is the term for a cross involving two traits?

The term for a cross involving two traits is a dihybrid cross.

In genetics, a dihybrid cross follows the inheritance of two different characteristics at the same time. Mendel’s classic example combined pea-seed shape—round or wrinkled—with seed color—yellow or green. Each trait was associated with a separate pair of hereditary factors, now understood as alleles of different genes.

When two plants heterozygous for both traits are crossed, the expected phenotypic ratio is 9:3:3:1. This result helped support Mendel’s law of independent assortment, which says that alleles of different genes can be distributed independently during gamete formation, provided the genes are not linked.

A dihybrid cross is not the same as a test cross: a test cross uses a homozygous recessive individual to reveal an unknown genotype. A monohybrid cross examines one trait, while a trihybrid cross examines three.