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The below mentioned article provides a short note on the Coupling and Repulsion Hypothesis of Gene.
Bateson and Punnett in 1906, described a cross in sweat pea, where failure of gene pairs to assort independently was exhibited. Plants of a sweat pea variety having blue flower (BB) and long pollen (LL) were crossed with those of another variety having red flower (bb) and round pollen (II). F1 individuals (BbLl) had blue flower and long pollen.
These were test crossed with plants having red flower and round pollen (bbll).
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In this case, the character for blue colour of flower is dominant over red colour, and long pollen character is dominant over round pollen. In case of independent assortment, one should expect 1:1:1:1 ratio in test cross. Instead 7:1:1:7 ratio was actually obtained, indicating that there was a tendency of dominant alleles to remain together.
The case was similar for recessive alleles also. This deviation was explained in terms of gametic coupling by Bateson.
It was also observed that when two such dominant alleles or recessive alleles come from different parents, they tend to remain separate. This was termed as gametic repulsion. In Bateson’s experiment, in repulsion phase, one parent would have blue flower and round pollen (BBII) and the other would have red flower and long pollen (bbLL).
The results of test cross in such a repulsion phase were similar to those obtained in coupling phase, giving 1:7:7:1 ratio instead of expected 1:1:1:1 (Fig. 8.1).
Bateson explained the lack of independent assortment by means of a hypothesis known as coupling and repulsion hypothesis. Later on, coupling and repulsion were discovered to be two different aspects of linkage.
