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Answers:
LEVEL: A2
BIOLOGY – Classification, biodiversity and evolution
13. Selective breeding (7 minutes)
(a) Modern farming practice has been very successful in the artificial selection of cattle for dairy
herds. A common breed is the large, black and white Friesian, the cows of which produce a
high milk yield. Both cows and bulls normally have their horns removed.
Name a feature in the description of Friesian cattle which provides an example of:
(i) Continuous variation.
(1 mark)
Size / the proportion of black to white / milk yield.
(ii) Discontinuous variation.
(1 mark)
Sex.
(iii) A non-inheritable characteristic.
(1 mark)
Absence of horns.
(b) Outline how cattle are bred selectively to produce a higher milk yield.
(2 marks)
Bulls known to sire high-yielding cows are crossed with cows that produce high milk yie ld.
Test the milk yield of the cows you have to breed from and select the cow with the highest milk yield
(A). Select a bull descended from a cow with a high milk yield (B). Cross A and B and select female
calves. Wait for three calves to mature and test their milk yield. Select the one with the highest milk
yield (C) and cross with a bull descended from a cow with a high milk yield. Repeat the process over
several generations.
(c) A possible consequence of selective breeding is that some breeds of cattle may become
extinct.
Suggest:
(i) Why it is important to conserve rare breeds.
(2 marks)
It maintains the gene pool and allows for out-breeding.
Copyright © Pearson Education Limited 2001
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Answers:
LEVEL: A2
BIOLOGY – Classification, biodiversity and evolution
(ii) What genetic problems might arise when maintaining a very small population of a rare breed
over many generations?
(3 marks)
Inbreeding causes loss of variability; undesirable characteristics are more likely to become fixed in the
population; in small populations genes can be lost / genetic drift.
(d) To what extent might genetic counselling be regarded as a form of artificial selection in
humans?
(1 mark)
The human gene pool could be altered because parents choose to avoid having children with certain
characteristics.
(Total marks 10)
Copyright © Pearson Education Limited 2001
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