Linkage
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Because of this reason, the genes carried in different chromosome undergo independent assortment which was explained so successfully by Mendel’s Principle.
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An organism may have numerous genes for its various phenotypic traits, but contain limited number of chromosomes.
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Each chromosome must contain many genes.
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Thus genes in the same chromosome will not be assorted independently.
- Mendel’s second principle, the law of independent assortment referring to the separation of two pairs of alleles independently has only limited application, and hence cannot be considered as a universal law.
- The second principle is valid only when two or more pairs of genes or alleles are situated in different chromosomes, enabling their independent assortment during the formation of gemetes.
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Sturtevant first showed that genes are arranged in a linear fashion on the chromosome.
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In 1906 Bateson and Punnett found two pairs of alleles in sweet Peas did not assort independently named this behaviour as coupling and repulsion phase.
 To view "Linkage Animation"
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Bateson and Punnett could not explain the exact reasons of coupling and repulsion.
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T.H. Morgan who while performing experiments with Drosophila, in 1911 proposed the new concept of "linkage".
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He proposed that each chromosome contains a collection of small units called genes and are arranged on the chromosome in a linear fashion.
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Each gene must reside on a particular chromosome and tend to be inherited together.
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All the genes on a chromosome are said to be linked to one another and belong to the same linkage group. The phenomenon of inheritance of linked genes in same linkage group is called linkage.
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He also suggested that the strength of linkage between genes depended on the distance between them on the chromosome.
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Last modified: Tuesday, 20 March 2012, 6:47 AM
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