7. A Drosophila melanogaster with tan body and red eyes, line A, is crosses with

Question

7. A Drosophila melanogaster with tan body and red eyes, line A, is crosses with a D. melanogaster with a black body and cinnabar eyes, Line B. Both lines are true breeding. The resulting offspring are all tan bodied with red eyes. One of the F1 females is crossed with a male from line B. The resulting F2 offspring are as follows: Tan body, red eyes 44 Tan body, cinnabar eyes 6 Black body, red eyes 8 Black body, cinnabar eyes 42

Are the two loci linked? What hypothesis do you implicitly test to find out? Do a chisquare test, cite your value and explain what it means.

If they are linked, how many map units apart are they?

What proportion of the gametes from the Line B males have the allele for black body and cinnabar eyes? What proportion of the gametes from the F1 males have the alleles for black body and cinnabar eyes?

Explanation / Answer

As the numbers of progeny that are parental type (86) are greater than the number of progenies that are recombinant (14) so this proves that this is a case of Linkage.

In chi square test the null hypothesis will be that the genes are unlinked.

On calculation with the formula= (O – E)/E

So chi square= {(86-50)/50} + {(14-50)/50}

                          = 0

As the p value <0.05, so the hypothesis is not corrected and can be rejected. This proves that the genes are linked.

The recombination frequency is found to be 0.14 in this case and recombinaron frequency is equal to map unit so the distance between the gene is 0.14 mu or 0.14 cM.

As there is no evidence for sex linked inheritance so the proportion of the gametes from the Line B males have the allele for black body , cinnabar eyes and proportion of the gametes from the F1 males have the alleles for black body and cinnabar eyes cannot be predicted.

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