Karnataka Board PUCPUC Science 2nd PUC Class 12

Mendelian Inheritance - Mendel’s Laws of Heredity - The Law of Segregation (Law of Purity of Gametes)

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Notes

Law of Segregation or Law of purity of gametes:

  • The Law of segregation states that “When a pair of contrasting factors are brought together in a F1 hybrid. The two factors of the allelic pair remain together without mixing and when gametes are formed, the two separate out, so that only one enters each gamete.” 
  • Law of Segregation is also known as the Law of Purity of Gametes because one gamete contains only one allele from each parent, so all gametes are always pure.

According to the law of segregation:

  1. Alleles do not show any blending, both characters are seen as such in the F2 generation although one of the characters is not seen in the F1 generation.
  2. Each organism contains two factors or alleles for each trait in its diploid cells and the factors segregate during the formation of gametes.
  3. Each gamete then contains only one factor from each pair of factors. The two alleles (contrasting characters) do not mix, alter or dilute each other and the gametes that are formed are 'pure' for the characters which they carry". 
  4. A homozygous parent produces similar gametes and a heterozygous parent produces two kinds of gametes each having one allele with equal proportion. Gametes are never hybrid. 
  5. During the formation of gametes, the factors or alleles of a pair separate and segregate from each other such that each gamete receives only one of the two factors.
  6. When Mendel crossed a homozygous tall plant with a homozygous dwarf plant, the offspring was discovered to be a hybrid tall plant (F1 generation). The resulting hybrid tall has two alleles: 'T' (tallness) and 't' (dwarfness). When this hybrid tall produces gametes, the two alleles, 'T' and 't', segregate as shown below:
  7. The appearance of a recessive trait in the F2 generation demonstrates the law of segregation. It is a universally applicable law.
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