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Genetic Linkage Analysis

You recently isolated a mutant in the fruit fly, Drosophila melanogaster, that results in the flies being unable to orientate themselves in a straight line, ie they continuously fly in circles. You have called this new mutation cir.

You suspect that the cir mutation is located on chromosome 2 close (within 5cM) of the withered wing gene whd.

Discuss fully the genetic crosses and subsequent analyses you would do to investigate your hypothesis.


Solution Preview

Let's call the dominant version of the flying-in-circles gene C, and let's call the recessive version c. Similarly, we have W and w for two versions of the withered wing gene.

What you would do is cross a fly that is heterozygous for both traits (CcWw) with one that is homozygous recessive for both traits (ccww). You would then look at the traits found in the offspring.

The heterozygous fly can have its genes arranged in two configurations:

C c OR c C
W w W w

(I.e. CW on one chromosome and cw on the other OR cW on one chromosome and Cw on the ...