What is the First law of Segregation?

Mendel observed that when pea plants with contrasting traits were crossed, the first generation (F₁) showed only the dominant trait. However, in the second generation (F₂), both dominant and recessive traits reappeared in a 3:1 ratio. From this, he proposed the Law of Segregation.

According to this law, a diploid organism passes on only one allele of a gene to its offspring, chosen randomly. During meiosis, the two alleles of a gene separate, and each gamete receives just one allele.

In a monohybrid cross, both alleles are expressed in the F₂ generation without blending, proving that gametes carry single alleles. The law rests on four key principles:

1. A gene can exist in multiple allele forms.
2. During meiosis, allele pairs separate so each gamete carries one allele.
3. Every organism inherits two alleles for each trait (one from each parent).
4. The two alleles differ in dominance, with one being dominant and the other recessive.