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).

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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