Principle of Segregation

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The Principle of Segregation

The principle of segregation by Gregor Johann Mendel, also known as Mendel's first law or law of equal segregation (Griffiths, Wessler, Carroll & Doebley. 2012, p. 32)[1], states that each characteristic of an organism is controlled by two alleles (gene occurring in pairs). During gametes formation in meiosis I, the alleles from each gene will segregate from each other and each gamete will only carry one of the alleles (Hartl & Ruvolo. 2012, p.85)[2].

The Principle of Segregation

Significance of the Discovery of Principle of Segregation

This law of equal segregation allows us to understand single-gene inheritance pattern. It also provides us with an insight as to how traits are being passed down from one generation (parent) to the subsequence generation (offspring).

Mendel’s Experiment

Main article: Mendelian Inheritance

In order to have a better grasp on the principle of segregation, we must first understand the experiment carried out by Gregor Mendel that eventually brought to the discovery of this principle.

Mendel began by crossing a pure-breeding (true-breeding) tall pea plant with another pure-breeding dwarf pea plant (parental generation, P1 generation). Following the crossed, he noticed that all progenies of the first filial (F1) generation grew into tall pea plants.
He then crossed a F1 plant with another F1 plant (selfing). The intercrossed of two F1 plants produced second filial (F2) generation with two different characteristics. F2 generation was a mixture of tall and dwarf pea plants. The ratio of tall pea plant to dwarf pea plant was roughly around 3:1 (75% of F2 generation grew into tall pea plants while 25% of the F2 generation grew into dwarf pea plant.).

Monohybrid crosses involving alleles controlling the stem length of pea plant that leaded to the discovery of the principle of segregation.


  1. GRIFFITHS, A.J.F., WESSLER, S.R., CARROLL, S.B. and DOEBLEY, J., (2012) Introduction to Genetic Analysis. Tenth ed. New York: W.H. Freeman and Company.
  2. HARTL, D.L. and RUVOLO, M. (2012) Genetics: Analysis of Genes and Genomes. Eighth ed. Burlington: Jones and Bartlett Learning.
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