The genes engrailed (en) and Ultrabithorax(Ubx) are both located on the second c

Question

The genes engrailed (en) and Ultrabithorax(Ubx) are both located on the second chromosome of Drosophila melanogaster. When a homozygous engrailed fly is mated with a homozygous Ultrabithorax fly in the F1 are all Ultrabithorax (which should not be a surprise). A testcross of the F1 females gives us the results below. What is the map distance between en and Ubx?

Wild type                            294

Ultrabithorax                        592

Engrailed                             573

Ultrabithorax, engrailed      268

Explanation / Answer

To calculate map distance between en and ubx we need to find percentage of recombination between them as:

Recombination Percentage = Number of recombinant offsprings X100 / total number of offsprings ----> (1)

The number of offsprings given for ultrabithorax, engrailed (Recombinant) = 268 and wild type is 294.

268+294= 562

The total number of offsprings=1727.

putting these values in (1) we get

recombination frequency = 562 X 100/1727

= 32.54%.

This means that the distance between en and Ubx is 32.54 cM or 32.54 m.u.

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