Linkage is the persistent association of genes which, without being separated during meiosis, are passed on from generation to generation in the same position on their chromosome, such genes are linked together and are present on the same chromosome. The principle of linkage was first discovered by Bateson and Punnett in 1906 in sweet pea (Lathyrus odoratus). Linkage is of two types – complete and incomplete. 

(a) Complete linkage – The genes closely located in the chromosome show complete linkage as they have no chance of separating by crossing over and are always transmitted together to the same gamete and same offspring. 

(b) Incomplete linkage – The genes distantly located in the chromosome show incomplete linkage because they have a chance of separation by crossing over and of going into different gametes and offsprings. 

Significance of linkage are as follows:– 

1. It greatly reduces the chances of the formation of new combinations of genes in the gametes. It, thus, helps in keeping the parental, racial and specific traits together. 

2. It helps in maintaining the valuable traits of a newly developed variety. 

3. It disallows the plant and animal breeders to combine all the desirable traits in single variety. 

4. It helps in ascertain exact position of genes and distances between them in chromosome.