DP Biology (last assessment 2024)

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Question 21N.2.HL.TZ0.2b.i

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Date November 2021 Marks available [Maximum mark: 1] Reference code 21N.2.HL.TZ0.2b.i
Level HL Paper 2 Time zone TZ0
Command term Draw Question number b.i Adapted from N/A
b.i.
[Maximum mark: 1]
21N.2.HL.TZ0.2b.i

The diagram shows the structure of two chromosomes after the first division of meiosis, assuming that there was no crossing over or chiasmata formation.

(b.i)

Draw the same chromosomes to show their structure at the same stage of meiosis if there had been one chiasma between two gene loci.

[1]

Markscheme

all four upper arms with one A and both chromosomes with one B and one b on the lower arms;

The chromatids can be shown as single lines rather than the wider versions in the question.

Examiners report

This was mostly well answered but some candidates showed one chromatid flopped over a non-sister chromatid, like crossed legs of a seated person, without any recombination having occurred. This showed a misunderstanding of the process of crossing over and chiasma formation. There were also a wide range of other answers showing confusion about events in meiosis.

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