# DBT JRF 2022 — Question 4

Exam: DBT JRF 2022 · Section: A · Topic: Epigenetics › DNA Methylation in Plants · Difficulty: Medium

## Question

The cytosine residues in the DNA are methylated at specific di- or trinucleotide sequences. Which among these methylation motifs are found predominantly in case of protein-coding genes in plants? H stands for A, T or C.

## Options

- **A.** CpG and CpHpG
- **B.** CpHpG and CpHpH
- **C.** CpGpG and CpHpH
- **D.** CpG and CpHpH

## Answer

Option B

## Explanation

DNA methylation context in plants (where H = A, T, or C): • CpG: Most conserved context; maintained by MET1 (homologue of mammalian DNMT1). • CpHpG: A plant-specific context; maintained by CMT3 methyltransferase. • CpHpH: Another plant-specific context; established by DRM2 and maintained by CMT2. For protein-coding gene bodies in plants, CpHpG and CpHpH methylation predominates (in addition to CpG). This is distinct from mammals, which rely almost exclusively on CpG methylation. CpGpG is not a standard methylation context and is a distracting option. Answer: CpHpG and CpHpH (Option 2).

Source: https://mypyqbuddy.com/questions/the-cytosine-residues-in-the-dna-are-methylated-6a104cd5920734408bc0c6e1