Question 23M.1.HL.TZ1.26
| Date | May 2023 | Marks available | [Maximum mark: 1] | Reference code | 23M.1.HL.TZ1.26 |
| Level | HL | Paper | 1 | Time zone | TZ1 |
| Command term | Question number | 26 | Adapted from | N/A |
DNA methylation profiles in zebrafish (Danio rerio) gametes were determined. The methylated areas were divided into three groups according to the amount of methylation: high, medium and low methylation.
[Source: Potok, M.E., Nix, D.A., Parnell, T.J. and Cairns, B.R., 2013.
Reprogramming the Maternal Zebrafish Genome afterFertilization to
Match the Paternal Methylation Pattern.
Cell, [e-journal] 153(4), pp. 759–772. http://dx.doi.org/10.1016/j.
cell.2013.04.030.]
Methylation of DNA in sperm and egg is removed immediately after fertilization. What is the reason for this?
A. Methylation allows RNA polymerase to join the promoter.
B. It is needed to form homologous pairs of chromosomes.
C. It allows expression of genes linked to early development.
D. Transcription of promoters only occurs in methylated genes.
[1]
C
A stacked bar chart was included as stimulus material but several teachers pointed out that it was not needed to answer the question. About half of candidates chose the expected answer but the discrimination index was relatively low, perhaps because the chart confused some conscientious candidates who studied it before answering.