A researcher conducted crosses between two different strains of Drosophila. 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

Singed bristles/vestigial wings and normal bristles/normal wings

Explanation:

The recombinant progeny might occur due to the crossing over of the homologous chromosomes in case of the  linked genes. This progeny are different from their parent progeny.

The F1 offspring obtained from the given cross in the question results in the normal wings and normal bristles ( SsLl). This progeny was crossed with singed bristles and vestigial wings (ssll). The progeny obtained from their cross are 'Sl' and 'sL' ( parental type ) and SL' or 'sl' ( recombinant).

Thus, the correct answer is option (D).

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

emerging idea only occurs as a raw idea that could appear out of nowhere. meanwhile, to reach scientific consensus , that idea must be structured and tested over and over again through various experiments. the scientific consensus transforms the raw idea into idea that is more reliable through the process of scientific elimination.