Photo AI
Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase - AQA - A-Level Biology - Question 9 - 2018 - Paper 2
Question 9
Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is essential to newborn mammals as milk is their only source of food. Most mammals... show full transcript
Worked Solution & Example Answer:Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase - AQA - A-Level Biology - Question 9 - 2018 - Paper 2
Step 1
Describe how farming cattle as a source of milk could have led to an increase in LP.
Answer
Farming cattle provided a reliable source of milk, which is rich in nutrients. Those individuals who could digest lactose (lactase persistence) were more likely to survive and reproduce, as milk provides essential nutrients for health. In environments where dairy farming was prevalent, individuals with the lactase persistence allele would have a reproductive advantage, leading to an increase in the allele's frequency in subsequent generations. This exemplifies directional selection based on the selective advantage conferred by the ability to digest milk.
Step 2
Use the information provided to explain why the number of people showing LP would rapidly increase once selection for this condition had been established.
Answer
Once lactase persistence was favored by natural selection, individuals with this trait would reproduce more successfully. As the beneficial allele increases in the population, the number of individuals able to digest lactose (showing LP) would also rise rapidly. This rapid increase occurs because the advantageous trait allows for better survival and more offspring in future generations.
Step 3
Suggest and explain how this mutation causes LP.
Answer
The mutation associated with lactase persistence likely occurs in a regulatory region upstream of the lactase gene, affecting its transcription. This mutation allows continuous expression of the lactase gene even into adulthood, resulting in the production of the lactase enzyme necessary for lactose digestion. As a result, individuals with this mutation maintain their ability to consume milk without adverse effects, leading to lactase persistence.