While studying a line of highly inbred flies, you have found a new autosomal rec

Question

While studying a line of highly inbred flies, you have found a new autosomal recessive mutation whose only phenotype is to cause males to use ridiculously elaborate courtship displays. You have named your new mutant royal wedding (rw) and want to map where it is on the autosome. You therefore cross it to a stock bearing two recessive markers on that chromosome, Wallace (w) and gromit (g), which you know flank rw (that is to say, the gene order is w rw g) and you create a homozygous w rw g tester stock. 1Why did you need to build the w rw g stock? Why couldn't you just test-cross the females to w g males? You then cross your rw stock to your w g stock to get heterozygous F1 females, and test-cross these females to your w rw g tester males. You then score your F2 progeny for these three traits, looking only at the male F2 progeny. w^+ rw g^+/w rw^+ g X w rw g/w rw g lb) Why can't you use the female F2 progeny in this experiment? If you are using 4th edition, do problems Ch7: 2, 4, 8, 15, 17, 18, 19, 23, 24, 27, 34

Explanation / Answer

1 (a) Presence of more than one different already marked markers on the same chromosome, helps in finding the location of unmapped mutant which can be estimated the seggregation of mutant relative to other markers on the chromosome. position of rw mutant can be found easily with respect to other two genes w and g on the same chromosome.

1(b) As we can see in F1 generation, the female have become heterozygous with wild type genes w+, g+ and rw+. And males are purely without any wild allele. So the males can only give correct mapping distance between the genes w, g and rw. So, there are more chances of following same pattern of inheritance by F2 generation. Thats why we are focussing on F2 males.

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