Question

Gregor Mendel used pea plants that were heterozygous for each of two traits—seed color and seed shape—to generate a dihybrid cross. The phenotypic ratio of the resulting offspring was nine with round and yellow seeds, three with round and green seeds, three with wrinkled and yellow seeds, and one with wrinkled and green seeds. From these results, what could Mendel conclude?
Traits are inherited as pairs, sets, or groups.
Traits that are dominant mask traits that are recessive.
Gametes carry one allele for each trait.
Traits are passed independently of one another.

Answer 1

All of them. Mendel’s 9:3:3:1 dihybrid result supports these conclusions:

- Traits are inherited as discrete units (alleles) that occur in pairs (one from each parent).
- One allele can be dominant and mask the effect of a recessive allele.
- Those paired alleles segregate so each gamete receives one allele for each trait (law of segregation).
- Different trait pairs assort independently into gametes (law of independent assortment), producing the 9:3:3:1 phenotypic ratio.