A researcher is studying linkage between singed bristles and vestigial wings, an
ID: 225764 • Letter: A
Question
A researcher is studying linkage between singed bristles and vestigial wings, and conducted crosses between two different strains of fruit flies. When true-breeding flies with singed bristles (s) and normal wings (L) were crossed to true-breeding flies with normal bristles (S) and vestigial wings (l), all F1 offspring had normal wings and normal bristles. The F1 offspring were crossed to flies with singed bristles and vestigial wings. Which F2 offspring is/are recombinant?
A.Singed bristles/vestigial wings only
B.Singed bristles/normal wings only
C.Singed bristles/normal wings and normal bristles/vestigial wings
D.Singed bristles/vestigial wings and normal bristles/normal wings
Explanation / Answer
Since the genes 's' and 'L' are linked,they will be passed on to the gamete together. The genes 'S' and 'l' are linked. Therefore,they will also be passed to the gamete together.
The cross would be as follows:
Parents: singed bristles and normal wings x normal bristles and vestigial wings
Genotype: ssLL SSll
Gametes: sL Sl
F1: SsLl ( normal bristles and normal wings )
Parents: normal bristles and normal wings x singed bristles and vestigial wings
Genotypes: SsLl ssll
Gametes: SL, Sl, sL, sl
As explained in the beginning,linked genes will be passed from F1 parent to the gametes together.Therefore, any gametes that the F1 parent produces with 'Sl' and 'sL' genes will be ''parental types'' and any gametes that F1 parent produces that are 'SL' or 'sl' will be ''recombinants''.
Therefore, flies with normal bristles & normal wings and singed bristles& vestigial wings are recombinants. Option 'D' is the correct answer.
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