iGCSE Biology (0610)-18.1 Variation – iGCSE Style Questions Paper 4

Question

Fig. 4.1 shows a wild pig and a Saddleback pig. The drawings are to the same scale.

(a) The Saddleback pig has been produced from the wild pig by artificial selection (selective breeding). Suggest two useful characteristics, visible in Fig. 4.1, which the farmers selected when breeding the Saddleback pig.
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(b) Explain how the Saddleback pig could have been produced by artificial selection.
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(c) There are different varieties of sheep. Some of these varieties have white wool and some have brown wool. The allele for white wool colour, N, is dominant to the allele for brown wool colour, n. A genetic diagram for the result of crossing a white-coloured sheep with a brown-coloured sheep is shown in Fig. 4.2. Complete the genetic diagram to show how wool colour is inherited in this cross.

Answer/Explanation

Ans:

(a) (selected for) greater volume/ larger animal/ higher yield of meat;
       smaller/ absent tusks;

(b) wild pigs allowed to breed;
      bigger pigs / pigs with small tusks selected (from offspring);
      repeat above procedure;
      for many generations;
     ‘saddleback’ type pigs interbreed/ not allowed to breed with wild pigs;

(c) parental genotype                             Nn× (nn);
      gametes                                           N + n × n + n;
      offspring genotype                                    Nn         nn           Nn          nn;
      offspring phenotype                          white        brown     white    (brown);

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