EXTENSION OF MENDELIAN GENETICS

EXTENSION OF MENDELIAN GENETICS

9.   EXTENSION OF MENDELIAN GENETICS

Bateson and Punnet were the followers of Mendelian genetics. They worked on sweet pea ( Lathyrus odoratus). They started with monohybrid cross in sweet pea and get the same ratio as Mendel i.e. 3:1. However, when they started the dihybrid ratio they get more parental types of plants rather than recombinant one. The dihybrid ratio deviated from typical 9:3:3:1. In the dihybrid cross, they crossed a red and long pollen plant with white and short pollen plant. In F2 generation almost all plants were parental. only a few plants were red and short pollen plants and white and long pollen plants. 
However, Bateson and Punnet were failed to explain the reason behind this result. Bateson later proposed a coupling and repulsion phenomena to explained it, but it was rejected later. The right explanation was provided by Morgon by his linkage theory.


9.1.    Coupling heterozygote 
When the dominant allele of both the genes are contributed by one parent and second parent contribute the recessive allele of a gene. The F1 produced by cross-fertilization is heterozygotes and it produces only red and long pollen plants, and white and short pollen plants.
9.2.    Repulsion heterozygote 
When one parent gives dominate allele of a gene and the second parent gives a dominant allele of other genes. Where a wild type allele of one gene is adjacent to a mutant allele of another gene on the same homologous chromosome. 


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