Explain the significance of crossing over and linkage.

Explanation

Significance of Crossing Over. 1. Crossing over is a means of introducing new combinations of genes and hence traits. 2. It increases variability which is useful for natural selection and adaptability under changed environment 3. It has proved that genes lie in a linear fashion in the chromosome. 4. Since the frequency of crossing over depends upon the distance between the two phenomenon is used for preparing linkage chromosome maps. 5. Useful recombinations produced by crossing over are picked up by breeders to produce useful new varieties of crop plants and animals. Green revolution has been achieved in Ind this selective picking up of useful recombinations. Operation flood or white revolution is carried out on the similar lines. Significance of Linkage. 1. Linkage groups and the phenomenon of crossing over show that genes are located on the chromosomes. 2. They maintain the specific racial and varietal traits of the organisms. 3. Because of linkages, improved varieties maintain their characteristics for long. 4. Lis, nges do not allow breeders to bring in all the useful traits in one variety. They have to thousands of individuals in order to obtain a correct combination of only a few traits which might come together due to crossing over. 5. A linkage group possesses various types of traits, some useful, others harmful. The two are difficult to separate. Therefore, harmful traits continue to be present even in improved varieties. Some of the early expressing genes can be used as marker genes to know the late expressing linked genes. 7. Two closely linked genes may nullify the effect of each other, e.g. fuzzy seeds and high ginning or naked seeds and low ginning in Cotton.