MSc II semester Paper III Unit 4 By Dr Tulika Mishra LINKAGE Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the ID: 1026083
Download Presentation The PPT/PDF document "Linkage and Crossing Over" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
1. Linkage and Crossing OverM.Sc II semesterPaper –III, Unit 4By Dr. Tulika Mishra
2. LINKAGEGenetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked. Genetic linkage is the most prominent exception to Gregor Mendel's Law of Independent Assortment. The first experiment to demonstrate linkage was carried out in 1905. At the time, the reason why certain traits tend to be inherited together was unknown. Later work revealed that genes are physical structures related by physical distance. The typical unit of genetic linkage is the centimorgan (cM). A distance of 1 cM between two markers means that the markers are separated to different chromosomes on average once per 100 meiotic product, thus once per 50 meioses...
3.
4.
5.
6. Complete Vs Incomplete Linkage
7. LINKAGE IS…
8.
9. How to check Linkage…If two genes are inherited from their parents to progeny= Link geneLinkage strength α 1/ Crossing overLinkage strength α 1/ distance between genesLinkage strength α 1/ Independent assortmentTEST CROSS is done to check linkage.Eg. If genes are completely linked then only Parental type gamete is formed… it indicates no crossing over.If they show Independent assortment then… along with Parental types..Recombinant are also formed in gametes.. Low linkageRecombination frequency No. of Recombinants = --------------------------- * 100 Total no of Progeny
10.
11.
12. Crossing over
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27. THANKS