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Date	May 2019	Marks available	3	Reference code	19M.2.SL.TZ2.2
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	Outline	Question number	2	Adapted from	N/A

Question

Identify the stage of mitosis labelled X in the image, giving a reason.

[1]

Outline the use of a karyogram during pregnancy.

[3]

Markscheme

telophase because the chromosomes/chromatids have reached the poles
OR
«late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔

OWTTE

a. is a photograph/diagram of homologous pairs of chromosomes that can be analysed ✔

b. information may be used to determine other chromosome abnormalities/changes in chromosome numbers/possible birth defects ✔

c. Down syndrome/trisomy can be detected if there are three copies of a chromosome Not just “Down syndrome”.
OR
accept any other valid example ✔

d. other missing or extra pieces of chromosomes can be detected ✔

e. sex can be determined as the Y chromosome is shorter than the X ✔ Or correct ref to X and Y.

Examiners report

Most were able to correctly state (late) anaphase or telophase but did not give a reason as clearly asked. Many students seem to have excellent eyesight as they claimed to see that the chromosomes were unwinding and that the nuclear membranes had formed. Please encourage the students not to go beyond what can be seen.

Most knew what a karyogram was. However, the question was about use, which does not involve a detailed description, taking up half the space about how the sample was obtained and the risks involved. Most knew that it was to do with the chromosomes, few stated that it was a diagram or a picture of the homologous pairs. An explanation of how it is used to confirm sex was needed.

Syllabus sections

Core » Topic 3: Genetics » 3.2 Chromosomes

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