Please Make it neat and clear In Drosophila, mutations in an autosomal gene call

ID: 168194 • Letter: P

Question

Please Make it neat and clear

In Drosophila, mutations in an autosomal gene called brown (br) result in flies with brown colored eyes. The wildtype allele (br+) results in red eyed flies. Mutations in another autosomal gene known as bar (bar) result in flies have a bar-shaped eyes, whereas the wildtype allele has normal eyes (bar+). The two genes (bar and brown) are 20 mu apart. A cross between a truebreeding brown eye female and a truebreeding bar shaped eye male results in F1 progeny that all have red eyes and bar-shaped eyes. a. A testcross was done with an F1 female and a tester male (homozygous recessive). If the 2 genes are 20 mu apart, determine how many flies with red bar-shaped eyes will result from the above cross if 1000 flies are scored. Show your work. b. Flow many red, bar shaped eye flies will result from the reciprocal testcross? Explain.

Explanation / Answer

In the given question, the two genes are 20 mu apart. The distance is measured in maximum 50 mu. That means the 20-mu distance is 40% of maximum recombination frequency 50mu, which means genes are 40% closer and 60% recombination.

Gametes

br+ bar+

br bar+

br+ bar

br bar

br+br bar+bar (red and normal)

brbr bar+bar (brown and normal

br+br barbar (red bar shape)

brbr barbar (bar and brown)

According the rule Mendel assortment: the genotype ratio should be 1:1:1:1

However, for the bar and brown eyes that ratio should vary because of 40% linkage. For Mendel inheritance, we assume the linkage should only 50%. Therefore, in the given ratio 10%, less linkage will occur, so 10% fewer ratios will found in case of bar and brown eyes offspring.

The net ratio for bar and brown eyes would be= 1 x 90% = 0.9

For 1000 offspring (score) the normal numbers are = 1000/4 = 250

However, through the recombination 250 of bar and brown will change to its 90% which is= 250x 90 % =225. Twenty-five offspring difference will be equally dividing to other offspring 25/3 8.

Now the net numbers of red bar shaped eyes offspring = 250+8 =258