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Date	May 2021	Marks available	1	Reference code	21M.1.SL.TZ1.18
Level	Standard level	Paper	Paper 1	Time zone	Time zone 1
Command term		Question number	18	Adapted from	N/A

Question

Which genotype would be normally found in a gamete?

A. Rr

B. RS

C. rStt

D. TUt

Markscheme

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.

Syllabus sections

Core » Topic 3: Genetics » 3.4 Inheritance

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