Which Mendelian law states that alleles segregate randomly during gamete formation?

The Mendelian law stating that alleles segregate randomly during gamete formation is the Law of Segregation. It says that the two alleles for a gene separate when reproductive cells form, so each gamete receives only one allele.

For example, a pea plant with two different alleles for a trait can pass either allele to its pollen or egg cells. At fertilization, the offspring receives one allele from each parent, restoring a pair. This explains why a recessive characteristic that disappears in the first hybrid generation can reappear in the next generation.

In a classic heterozygous cross, the expected genotype ratio is 1:2:1: one homozygous dominant, two heterozygous, and one homozygous recessive combination. When complete dominance applies, those genotypes produce a familiar 3:1 phenotype ratio. Mendel inferred these patterns from repeated pea-plant crosses.

The Law of Segregation is sometimes called Mendel’s First Law, although historical treatments differ in how they order his principles. It should not be confused with the Law of Independent Assortment, which concerns how allele pairs for different traits are inherited relative to one another.