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Answer step by step. thank you. 1) Gene loci in testcross              Recombination frequency (%)             a...

Answer step by step. thank you.

1)

Gene loci in testcross              Recombination frequency (%)

            a and b                                                50

            a and c                                                50

            a and d                                                50

            b and c                                                20

            b and d                                                10

            c and d                                                 28

Are all the genes linked? Are some of the genes linked? If so how many linkage groups are there?

Can you determine the order of the genes on the chromosome? If so, what is the order?

2)

Three corn genes, R, D and Y lie on chromosome 9. The map of the three genes, using map units is:
            20        40
R -------D--------------Y

A heterozygous plant (R D Y/r d y) is crossed with a testcross parent (r d y/r d y) :

how many double cross over progeny would be expected in a progeny of 1000 if there were no interference?

What is the interference if there are 50 DCOs?

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Answer #1

Genetic linkage refers to the close positioning of the genes on the same chromosome so that they are inherited together and do not assort independently. Recombination frequencies give an estimate of the distance between genes on the chromosomes. A larger recombination frequency indicates that the genes are most likely far apart and vice versa. 50% value indicates maximum recombination frequency measured betweeen genes indicating unlinked genes.

In the above question, all genes are not linked. The genes showing 50% recombination frequency are not linked. Some of the genes are linked showing recombination frequency less than 50% i.e.b and d, b and c, c and d.

The order of the genes on the chromosome can be determined by creating a linkage map using the data as follows-  

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