@A. Patil,
To my mind, linkage drag is the transfer of something, which is not desirable/required along with the gene of interest. To remove this, back cross method can be used. But this method may or may not be successful. Because the removal of linkage drag depends upon the type of linkage between the genes. If it is complete linkage, it may be difficult to remove that drag.
Regards
The closer the linkage between loci, the more difficult to separate the loci (the higher the linkage drag). To be able to separate such loci will require a large number of progeny of more generation of back cross breeding. However, with the advance of molecular marker technology, you may have a better chance to remove linkage drag.
If you have access to marker technology, you can combine back crossing and background and foreground selection for molecular markers. However, (1) you will need to have marker loci closely associated with the desirable character in the donor parent and you will use these markers as background selection to indirectly indicate the presence the characters in segregated populations. (2) You will also need to have high density map of the recurrent parent (the tester) to identity the individual carrying the most genetic background of the recurrent parent among segregated back cross progeny.
Once you did your BC and obtain BC1 segregated population, you will screen among the progeny for marker associated with the trait/gene that you want to introgres from the donor into the recurrent genetic background. You will want to identify the progeny carrying the linked-marker (and eventually in it carries the trait/gene) Subsequently, all progeny positively identified as carrying the linked-markers, were subjected to foreground molecular marker analysis.
What you want to find are progeny that are positively carrying back ground markers, and as many as possible carrying the foreground marker loci. The more-the foreground markers are presence, the closer the selected progeny to the recurrent parent and the less genetic background of the donor existed in the genome of the selected progeny. Such condition means the less linkage drag will be seen in the selected progeny.
Hi,
Breeders use backcross scheme to remove Linkage drag, but in some cases it won't work even after many runs of backcrossing. The remaining 'linkage drag' may have negative impact on the elite lines used to cross with.
There is one molecular technology called 'Site-specific recombination', which can be a useful tool to remove the linkage drag without the tedious process of backcrossing. See attached paper-- see Fig. 5.
Best,
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