DP Biology (first assessment 2025)

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Question 21M.1A.SL.TZ1.18

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Date May 2021 Marks available [Maximum mark: 1] Reference code 21M.1A.SL.TZ1.18
Level SL Paper 1A Time zone TZ1
Command term Question number 18 Adapted from N/A
18.
[Maximum mark: 1]
21M.1A.SL.TZ1.18

Which genotype would be normally found in a gamete?

A. Rr

B. RS

C. rStt

D. TUt

[1]

Markscheme

B

Examiners report

This question proved to be too difficult, with fewer candidates answering it correctly than at the guess-rate of 25 %. To answer correctly, candidates had to appreciate that upper- and lower-case letters are used for dominant and recessive alleles of a gene and that in a haploid gamete there is only one allele of each gene. The only possible answer was therefore RS. Nearly four times as many candidates chose Rr instead. This was the first of the four answers so perhaps some candidates did not read beyond it. The advice is always to read all four answers, even if the first one seems beguilingly attractive.

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