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Linkage and Crossing Over Between Genes - After Sutton suggested the chromosomal theory of inheritance in 1903. evidence accumulated for the idea that genes were located on the chromosome.

Morgan showed that there could be genes more than chromosomes.

Sturtevant first showed that genes are arranged in a linear fashion on the chromosome.

The concept of presence of genes on chromosomes is universally accepted.

But genes present on single chromosome move together to the same pole in every meiosis step.

As a consequence such genes would fail to show independent segregation. But in real situation when a test cross is carried in pea plant (flower colour and pollen shape) the result showed 7: 1 : 1 : 7 ratio instead of 1 : 1 : 1 : 1 ratio as per Mendelian law of independent segregation.

Bateson and Punnett observed these variations and were puzzled. Hence they named this peculiar behaviour as coupling and repulsion phase. But Morgan in 1911 proposed the new concept of linkage.

1. Genes are arranged on the chromosome in a linear fashion.

2. Genes located in the same chromosome tend to stay together during every generation or inheritance.

3. The distance between two genes decides whether they will be inherited together and if so with what frequency.

 
 

 
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