Genetic Linkage

Genetic informations are inherited to offspring only through specific genes or alleles. The genes that are close together establish a linkage between two alleles. The genetic informations are transferred during meiosis stage of cell division. To begin with chromosomes of maternal and paternal cells are transmitted. This transmission helps in genetic information exchange. After intertwining they get separated resulting in the formation of offspring. Recombinants are produced by new combination of maternal and paternal traits.

Crossing over occurs during linkage of genes. Some changes can take place without the help of phenotype and independently on each other traits in independent assortment mannerism. Genes inherited on same chromosomes are genetically linked. When genes are inherited between different loci on chromosomes recombinants are produced. For instance, in fruit fly Drosophila melanogaster wing alleles and eye color alleles get inherited when they are present in the same chromosome.

History

British scientist William Bateson and Reginald Punnett were the first to discover the genetic linkage right after the discovery of Mendel’s laws. Thomas Hunt Morgan made efforts to understand the theory behind genetic information exchange. The distance between the genes can be easily traced by mapping of genetic links. The distance is measured in terms of centimorgan or genetic map unit. Centimorgan is nothing but a  product of meiosis equalling hundred recombinants. With the help of recombinant occurrence, it is possible to calculate the distance between two genes which are genetically inherited. When the distance between genes is more, the occurrence of non sister chromatids are prevalent.This is studied by Scientist Alfred Sturtevant. Haldane mapping function will represent the recombinant occurrence statistically.

Linkage map

Linkage map helps in positioning of alleles or genes with the help of genetic markers. Genetic markers aids in calculation of distance between phenotypes, for instance, eye color of fruit fly or microbial enzyme production which may result in genetic diseases. If recombination frequency is more, then the distance between the genes that are located on chromosome are more and vice versa. Recombination frequency is a frequency of single cross-over between chromosomes during meiosis cell division cycle. There is no recombinant production when double cross- over occurs.