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JAMB Biology 1990 Question 37

Question 37

Mendelian Inheritance

What would be the result of the first filial generation (F1) and the second filial generation (F2) of a monohybrid cross between pure line normal-winged Drosophila flies and pure line short-winged flies, if the gene for the normal wing is dominant?

  1. A.F1 flies all short-winged and F2 flies all normal-winged
  2. B.F1 flies all normal-winged and F2 flies all short-winged
  3. C.F1 flies all short-winged and three-quarters of F2 flies are short-winged
  4. D.F1 flies all normal-winged and three-quarters of F2 flies are normal-winged
Show the answer and explanation

Answer: D (F1 flies all normal-winged and three-quarters of F2 flies are normal-winged)

Explanation

NN × nn gives all Nn (normal) in F1; Nn × Nn gives 3 normal : 1 short in F2.