WAEC Biology 2011 Theory — Question 15
Question 15 of 27 from the West African Examinations Council (WAEC) Biology 2011 Theory paper, with the correct answer and a full explanation.
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4(b) In a breeding experiment a homozygous dog (BB) was crossed with a homozygous white dog (bb) to produce black puppies in the first filial generation (F1). The second filial generation produced a total of two hundred and forty (240) black and white puppies. With the aid of a genetic diagram, determine: (i) the number of white puppies (ii) the number of black puppies in the second filial generation.
Model answer
Since the original parents are BB and bb, all of the F1 will be Bb (black). Crossing F1 x F1 (Bb x Bb) gives F2 ratio BB:Bb:Bb:bb = 1 black : 2 black : 1 white, i.e. 3 black : 1 white. (i) Number of white puppies = 1/4 x 240 = 60. (ii) Number of black puppies = 3/4 x 240 = 180.
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