DP Biology (last assessment 2024)

Test builder »

Question 23M.3.HL.TZ1.12

Select a Test
Date May 2023 Marks available [Maximum mark: 5] Reference code 23M.3.HL.TZ1.12
Level HL Paper 3 Time zone TZ1
Command term Explain, Outline, State Question number 12 Adapted from N/A
12.
[Maximum mark: 5]
23M.3.HL.TZ1.12

The diagram shows the steps in preparing a DNA microarray to detect cancer in a patient.

[Source: Diagram of typical dual-colour microarray experiment, n.d. [online] Available at: https://www.wikiwand.com/en/DNA_
microarray [Accessed 8 March 2022]. Public domain.]

 

(a)

Outline the reason that DNA is labelled with synthetic dyes Cy3 and Cy5.

[1]

Markscheme

fluorescent/coloured to be identified later;

Examiners report

Many could give a reason why DNA in microarrays is dyed.

(b)

State the type of DNA produced by reverse transcriptase.

[1]

Markscheme

cDNA/copy DNA;

Examiners report

Many could get the mark for correctly stating cDNA as the type of DNA produced by reverse transcriptase.

(c)

Explain how a microarray detects gene expression.

[3]

Markscheme
  1. (single strand) DNA molecules /sequences/probes attached to a slide/small surface;
  2. there are numerous sequences of DNA/genes in one microarray;
  3. probes bind to/hybridize with cDNA which has been coloured/labelled;
  4. the microarray is scanned to detect different colours
    OR
    colours show which genes have been expressed;
Examiners report

This question was answered very poorly by most candidates, showing only a very superficial knowledge of microarrays.