CAIE A Level Biology 9700 · Selection and evolution
A dairy farmer has been selectively breeding her herd of cows to increase milk yield over many generations. Initially, the average milk yield was 20 litres per day. After 50 years of selective breeding, the average yield is now 35 litres per day. Explain how selective breeding has led to this increase in milk yield. Include in your answer the genetic principles involved and any potential negative consequences.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.