Biology · Principles of Inheritance and Variation · NEET
A parent has two alleles for a gene (for example T and t). When the parent makes gametes (eggs or pollen), these two alleles separate. One gamete gets T, another gamete gets t. No gamete gets both. So half the gametes carry one allele and half carry the other. This separation is what we call segregation.
Because each gamete stays PURE for one allele — it carries only one, never a mixture of both. Even in a Tt parent, the T and t do not blend inside a gamete. A gamete is either T or t, clean and pure. That is why the two names mean the same law.
They separate during MEIOSIS, when gametes are formed. The two alleles of a gene sit on two homologous chromosomes. When these homologous chromosomes separate (in Anaphase I of meiosis), the alleles they carry go to different cells. So meiosis is the physical reason behind segregation. This link was later explained by the Chromosomal Theory of Inheritance.
Law of Dominance explains what you SEE — in a Tt plant, only the dominant trait (tall) shows in F1. Law of Segregation explains what happens INSIDE during gamete formation — the alleles separate so the hidden recessive can reappear in F2. Dominance explains the 3:1 look; segregation explains WHY the recessive comes back and gives the 1 in that 3:1.
Yes. This is a common NEET trap. Even in incomplete dominance, the alleles still separate cleanly during gamete formation. In Snapdragon, red (RR) x white (rr) gives pink (Rr) F1, and selfing gives 1 Red : 2 Pink : 1 White in F2. The red and white parents REAPPEAR in F2 — that only happens because the alleles were pure and segregated. So the Law of Segregation ALWAYS applies; only the Law of Dominance changes.
In a Tt x Tt cross, each parent's alleles segregate, so gametes are 1/2 T and 1/2 t. When they combine randomly: TT, Tt, Tt, tt. Genotype ratio is 1:2:1. Because T is dominant, the phenotype is 3 tall : 1 dwarf. The recessive dwarf reappears only because the alleles stayed pure and separated.
In Antirrhinum (Snapdragon), a red flower was crossed with a white flower and in F1 generation pink flowers were obtained. When pink flowers were selfed, the F2 generation showed white, red and pink flowers. Choose the incorrect statement from the following:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Gregor Johann Mendel proposed it from his monohybrid crosses on garden pea (Pisum sativum). It is called Mendel's Second Law of Inheritance.
Yes. Both names describe the same idea: the two alleles separate during gamete formation, so each gamete carries only one pure allele.
Yes, it is considered a universal law with no known exception, because it depends on the separation of homologous chromosomes during meiosis, which happens in all sexually reproducing organisms.
Segregation deals with ONE gene pair separating during gamete formation. Independent assortment (Mendel's Third Law) deals with TWO or more gene pairs separating independently of each other.
