Principles of Genetics and Breeding

2.1.3 Mendel's explanation

• Mendel visualized the determinants of the characters, the factors or elements (later gene by Johannsen, 1909).
• According to Mendel each male and female parent contained a pair of such hereditary factors and each parent passed only one factor of a pair to the offsprings. The hereditary factors determine the characters. Further, he predicted each factor retained its originality from generation to generation and it was not modified in the hybrid.
• T and t alleles though remain together in F₁ does not contaminate or mix with one another and both alleles segregate to produce gametes for (T) dominant and (t) recessive alleles in F₂ and the phenotypic ratio is 3:1.

1. Law of segregation or law of purity of gametes states that "during the formation of gametes the 2 alleles responsible for a trait separate from each other. Alleles for a trait are then recombined at fertilization, providing the genotype for the traits of the offspring".

Law of segregation has universal application and occur both in plants and animals. To formulate this law Mendel considered monohybrid cross and noted the behaviour of a single pair of traits and single pair of alleles of a gene at a time.