What Is the “Law of Segregation” in Biology?

US Department of Agriculture/CC-BY-2.0

In biology, the law of segregation explains how the offspring of parents with similar characteristics sometimes have offspring with a different characteristic. It is one of the rules regarding genetics discovered by Gregor Mendel in the 1860s. According to this law, the two alleles, which form a gene, separate during the formation of the reproductive cells and recombine as the two parent cells join, determining the genetics of an offspring.

Mendel’s studies involved peas. He observed that peas planted from two plants that produced green peas sometimes created yellow peas. Mendel’s observations led him to believe there were dominant and recessive genes. The separation of the alleles allows the offspring to develop the traits that vary from the parent.

In humans, eye color follows Mendel’s law of separation. Blue eyes are a recessive gene and brown is a dominant gene. Due to the separation factor, two parents with brown eyes sometimes have a child with blue eyes. In these parents, both have a hybrid gene for brown eyes and the dominant brown color masks the recessive blue. However, if one parent has a pure brown eye color, all the offspring have brown eyes. If both parents have blue eyes, the offspring all have blue eyes.