The hereditary units or genes which determine the characters of an
Individual are carried in chromosomes and individual usually has many genes for determination of various different characters. As there are more genes than the chromosome it expected that each chromosome Contain more than one gene.
Genes for different characters may be either situated in same chromosome or in different chromosomes when genes situated in different chromosome, they assort independently according to Mendel’s law of independent assortment. But if the genes are situated in same chromosome and are fairly close to each other they tend to be inherited together this type of coexistence of two or more genes in the same chromosome is known as linkage. Linked genes do not assort independently but tend to stay together in same combination
- Suttons View on linkage: Sutton predicted that the bearer of genes and since number of genes are much more then chromosomes. He also stated that chromosomes move during meiosis of gamete formation. All the genes which are situated on same chromosome will be linked Together Sutton could not prove this experimentally
- Bateson and punnet found different result in a dihybrid cross in lathyrus odorotus while crossing purple flower and long pollen (PPLL) with red flower and round pollen (ppll) they found deviation from f2 ratio of Mendel they obtain purple long, purple round, red long and red round In the ratio of 14:1:1:3 respectively in f2 generation now combinations like Purple round and red long are of lesser frequency in f2 generation they Were again surprised to obtain the ratio of 7:1:1:7 in test cross as compared to expected ratio of 1:1:1:1 Bateson & punnet coined the Term coupling referring the situation were two dominant alleles of two genes are present in one parent and two recessive alleles in other parent. Thus both dominant passes into one gamete and both recessive passes into one gamete of another parent.
- Term repulsion used when parents were heterozygote such as cross
Ppll × Ppll. In these two dominant alleles of genes comes from different body of parents they are said to be in repulsion.
According to MORGAN: degree of linkage depends upon the distance between the linked genes in the chromosome. Morgan’s concept about the linkage developed the theory of linear arrangement of genes in chromosomes which helped the cytogeneticists in the construction of genetic Map & linkage Map of Chromosome.