3. Below is a genetic map of some DNA from a plant genomes. At top is a wild-typ

Question

3. Below is a genetic map of some DNA from a plant genomes. At top is a wild-type plant, followed below by three different mutants created by X-ray mutagenesis. Each hatch mark represents a map. As an example, in the wild-type plant D and E are 10 map units apart You mate each plant to a tester strain then cross the FI back to the same tester strain. For each of these plants I-IV, calculate the % of the testrossed Fls that would be De in phenotype, and the % that would be Dg in phenotype. Standard genetic nomenclature is being used here. D wldpe De G B D De Deletion Inversion D e

Explanation / Answer

1- Distance between D and E is 10 map unit.

So maximum percentage of recombinant that can be produced by DE will be 10%. When we test cross D E with d e we will get following types of progenies

DE, de, De and dE.

Out of which De and dE will be recombinant types which be 10% of the total progeny.

So progeny which will have De genotype will be 5% and dE will be 5%

The distance between D and G is 55 map unit.

So maximum percentage of recombinant that can be produced by DG will be 50%. Maximum percentage of recombinant progeny, in any case, will be maximum 50%. When we test cross D G with d g we will get following types of progenies

DG, dg, Dg, and dG.

Out of which Dg and dG will be recombinant types which be 10% of the total progeny.

So progeny which will have Dg genotype will be 25% and dG will be 25%

2- In this case Gene E and F are deleted as a result of the distance between the D and G is reduced to 25 map unit from 55 map unit.

Since gene E is deleted so we will not get any recombinant progeny which have De genotype.

In case of Dg we will get 12.5% of progeny which have Dg genotype.

3 -In this case due to inversion distance between D and E gene is increased to 30 map unit.

So the percentage of recombinant progeny which have De genotype will be 12.5%.

Upon inversion, the distance between the D and G will remain same.

So the percentage of progeny which have Dg genotype will be 25%.

4- In this case, D and E genes are present on the same chromosome whereas gene G is present on the other chromosome.

Crossing over takes place between the homologous chromosome. So there will not be any progeny which have Dg genotype

The distance between D and E is 10 map unit.

So progeny which will have De genotype will be 5%

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