Q26

Criteria	Marks
Identifies variation in lactose tolerance with reference to stimulus<br>Provides reasons for the variation with detailed reference to evolution and DNA	5
Identifies variation in lactose tolerance with reference to stimulus<br>Provides reasons for the variation with some reference to evolution and DNA	4
Identifies variation in lactose tolerance with some reference to stimulus<br>Provides reason(s) for distribution of lactose tolerance with some reference to evolution OR DNA	3
Identifies variation in lactose tolerance with some reference to stimulus<br>Provides a suitable reason for the distribution of lactose tolerance	2
Provides some relevant information	1

Sample answer:

The map shows that ability to digest lactose varies in adult populations around the world. For example it is much lower in Australia than Northern Europe. This variation is likely to be due to natural selection where the presence of milk in the diet is the selective pressure. A mutation to a gene is likely to cause the continued production of lactase past the age of five years. Adults who possess the mutation are likely to have an increased chance of survival as they have increased nutrition in their diets. They then reproduce and pass the mutation on to their offspring, making it more common in the population. Populations that have remained largely lactose intolerant are less likely to have had milk available and thus a mutation of the lactase gene would not offer any advantage and would not become more common in the population.