Illustrated · 1 min
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How Genes Separate
The Law of Segregation says that organisms have two copies of every gene and that they get one copy of each gene from each parent. It is one of Gregor Mendel's laws of inheritance. This is closely tied to the Law of Independent Assortment, which says that during gamete formation, genes for different traits segregate independently of each other.
Here's an example of the law of segregation in action:
In this imaginary lumpy species, the gene for (more lumpy) is dominant to the gene (less lumpy). Two heterozygous lumpies with genotype (meaning they have one dominant allele and one recessive allele) mate and have children. The results of this monohybrid cross are as follows:
Image source: By Sylvia Freeman
We can see that the dominant and recessive alleles from the parents have been distributed to the offspring. As a result, each of the offspring has two alleles for this trait.
On a molecular level, the law works because of how chromosomes separate during meiosis.
When we form gametes during meiosis, the homologous chromosomes get randomly separated into daughter cells. The result is that gametes have half the normal number of chromosomes. Diploid organisms, like humans, have two copies of every chromosome, so their gametes are haploid. Haploid gametes come together during fertilization to form a diploid zygote.
