Linkage, Haemophilia, Genes, Maize, Drosophila, Inheritance, Chromosomes, Sweet pea, Pollen grains, Linear fashion

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Linkage
Linkage is defined as the tendency of two or more genes to remain together in the original combination in the same chromosome during the process of inheritance for a number of generations. All the genes on a chromosome are said to be linked to one another.
Linkage was discovered by T.H. Morgan.
Linkage was found in Drosophila, sweet peas, maize, man, etc.
In Drosophila, the genes of body colour and nature of wings are linked and located on the same chromosome.
In sweet pea, the genes of flower colour and size of pollen grains are linked.
In maize, the genes for colour and shape of seeds are linked.
In man, the genes for haemophilia and colour blindness are linked.

T.H. Morgan (1911) proposed the theory of linkage based on his experiments in Drosophila. The theory of linkage explains the main principles of linkage. They are the following:
1. A chromosome contains many genes.
2. The genes are arranged in a linear fashion on the chromosome
3. The genes present in a chromosome are chromosome linked.
4. The linked genes are inherited together from the parents to the offspring.
5. Linkage is a rare phenomenon when compard to crossing over.
6. The strength of linkage depends on the distance between the linked genes. Closely located genes show strong linkage. Widely located genes show weak linkage.

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