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. (Note: assume that neither of these genes is X-linked.) The F1 offspring were then crossed to flies with singed bristles and vestigial wings. For the F2 offspring, what genotypes and phenotypes are possible

The correct answer is -

Possible F2 offspring genotypes and phenotypes:

SsLl: normal bristle, normal wing

Ssll: normal bristle, vestigial wing

ssLl: singed bristle, normal wing

ssll: singed bristle, vestigial wing

Explanation:

In this case, the genes 's' and 'L' and genes 'S' and 'l' are linked, they will be passed on to the gamete together.

The cross would be as follows:

F1:

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 )        

For F2,

Parents: normal bristles and normal wings    x   singed bristles and vestigial wings

Genotypes:            SsLl                                                         ssll

Gametes:                               SL, Sl, sL, sl

Cross:  

          SL        Sl         sL        sl

sl       SsLl     Ssll       ssLl      ssll

Thus the possible offspring will have -

SsLl: normal bristle, normal wing

Ssll: normal bristle, vestigial wing

ssLl: singed bristle, normal wing

ssll: singed bristle, vestigial wing

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