DP Biology (first assessment 2025)

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Question 23M.1A.SL.TZ1.21

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Date May 2023 Marks available [Maximum mark: 1] Reference code 23M.1A.SL.TZ1.21
Level SL Paper 1A Time zone TZ1
Command term Question number 21 Adapted from N/A
21.
[Maximum mark: 1]
23M.1A.SL.TZ1.21

The ability to digest lactose in adulthood appeared due to a mutation in the lactase gene. The frequency of the lactase persistence allele was recorded as 0.8 in present-day European populations and as 0.05 in fossils from populations of their prehistoric ancestors.

What could have caused the change in the allele frequency?


A.  Drinking more milk caused the mutation to occur.

B.  There was a strong positive selection for the lactase persistence allele.

C.  Lactase persistence was transferred to humans from cows.

D.  Prehistoric milk did not contain lactose.

[1]

Markscheme

B

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