You have a drosophila line that is homozygous for autosomal recessive alleles a,

Question

You have a drosophila line that is homozygous for autosomal recessive alleles a,b, and c, linked in that order. You cross females of this line with males homozygous for the corresponding wild-type alleles. You then cross the F1 heterozygous males withe their heterozygous sisters. You obtain the following F2 phenotypes (where letters denote recessive phenotypes and pluses denote wild-type phenotypes): 1364 +++, 365 abc, 87 ab+, 84 ++c, 47 a++, 44+bc, 5 a+c, and 4 +b+.

A. What is the recombinant frequency between a and b? Between b and c? (Remember there is no crossing over in drosophila males)

B. what is the coefficient of confidence?

Explanation / Answer

This is straight out of the solutions manual. I don't understand it either, so I'm not sure that I can explain it better than this: "This problem is somewhat simplified by the fact that recombination does not occur in male Drosophila. Also, only progeny that received the a b c chromosome from the male will be distinguishable among the F2 progeny. a.) Because you cannot distinguish between a^+ b^+ c^+/a^+ b^+ c^+ and a^+ b^+ c^+/ a b c, use the frequency of abc/abc to estimate the frequency of a^+ b^+ c^+ (parental) gametes from the female. parentals 730 (2*365) CO-ab: 91 (ab^+c^+,a^+bc= 47+44) CO b-c: 171 (abc^+, a^+b^+c= 87+84) DCO: 9 (a^+bc^+, ab^+c= 4+5) ------ 1001 a-b: 100%(91+9)/1001= 10 m.u. b-c: 100%(171+9)/1001= 18 m.u. b.) Coefficient of coincidence = (observed DCO)/(expected DCO)=9/[(0.1)(0.18)(1001)]=0.5"

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