The law of segregation is one of the fundamental principles of genetics discovered by Gregor Mendel. It states that during the formation of gametes (sex cells), the two alleles (alternate forms of a gene) responsible for a trait separate from each other so that each gamete receives only one of the two alleles.


Mendel's experiments with pea plants revealed that each plant possessed two alleles for each trait, one inherited from each parent. These alleles could be either dominant or recessive. Dominant alleles mask the expression of recessive alleles, and they are expressed in the phenotype of an organism. On the other hand, recessive alleles are only expressed in the phenotype when two copies of the same allele are present.

When gametes are formed, each parent contributes one allele for each trait. These alleles separate during the formation of gametes, so each gamete carries only one allele. During fertilization, the gametes combine, and the resulting zygote (fertilized egg) receives two alleles for each trait, one from each parent.


To illustrate the law of segregation, let's consider the inheritance of flower color in pea plants. Suppose we have a pea plant with the genotype Aa, where A represents the dominant allele for purple flowers and a represents the recessive allele for white flowers. When this plant produces gametes, the A and a alleles separate, so half of the gametes carry the A allele and the other half carry the a allele.

Suppose this plant is crossed with another pea plant with the same genotype, Aa. The resulting offspring will inherit one allele from each parent, so there are four possible combinations: AA, Aa, aA, and aa. Because the A allele is dominant, the AA and Aa genotypes will have purple flowers, while the aa genotype will have white flowers.


The law of segregation explains how traits are passed from parents to offspring and why offspring can inherit different combinations of alleles from their parents. This law is essential for understanding the principles of genetics and predicting the outcomes of genetic crosses.