AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

TYPES OF LINKAGE

• All the genes, which are linked with another, form a linkage group.
• Since linked genes are present in the same chromosome, the number of linkage group in an animal or plant is equal to the haploid number of chromosomes present in one cell.
• Linkage is an exception to Random Assortment.

Kinds of Linkage

• The phenomenon of linkage is of following two kinds
• Complete linkage
  • A phenomenon in which two or more genes of characteristics inherited together for a number of generations.
  • In these genes are closely situated in the chromosome and there occurs no breakage in between them.
  • Only combinations of parental characteristics are recovered in test cross progeny.
  • Complete linkage is seen only in male Drosophila.
• Incomplete Linkage
• In in-complete linkage the linked genes do not always stay together because homologus non-sister chromatids may exchange segments of varying length (which bearing many linked genes) with one another during meiotic prophase, by the process of crossing over and lead to recombinants.
• Here the recombinant types are also recovered along with parental types in the test cross progeny.
• Examples : seen in female Drosophila, Pea, Zea mays (maize), Tomato, Mice, Poultry and Man. Here, the examples of linkage have been considered only for Drosophila

To view "Incomplete Linkage Animation"