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Epigenetics, Genomic Imprinting and Mitochondrial Inheritance Quiz
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In epigenetic regulation, what roles do writers, erasers and readers perform?
- A Writers add marks, erasers remove them and readers bind marked sites and recruit partners You picked ✓
- B Writers add marks, erasers remove them and readers bind marked sites but do not recruit any partners You picked ✕
- C Writers add marks, erasers remove them and readers bind DNA sequences and alter them You picked ✕
- D Writers add marks, erasers remove them and readers bind unmarked DNA sequences and recruit partners You picked ✕
- E Writers add marks, erasers remove them and readers bind marked sites and remove them You picked ✕
Correct!
Incorrect
The answer is A: Writers add marks, erasers remove them and readers bind marked sites and recruit partners
Explanation
Why A is correct
See Epigenetic Regulation. Option A is correct because epigenetic regulation changes how genes are used without changing the order of DNA bases, and this can be organised into three roles. Writers add a chemical mark, for example DNA methyltransferases add methyl groups to DNA and other enzymes add marks to histones (the spool-like proteins around which DNA is wound). Erasers remove the mark, which is why epigenetic states can in principle be reversed. Readers are proteins that bind the marked site and recruit other proteins, such as complexes that open or compact chromatin (DNA packaged with its proteins). The mark is therefore not an isolated on-off switch: its effect depends on where it sits in the genome, which reader binds it and the surrounding chromatin. This is why crude statements such as "methylation always switches genes off" are too simple. The classic trap is to confuse an epigenetic change with a mutation; a mutation alters the DNA sequence, while an epigenetic state alters the use of an unchanged sequence. To keep the three roles apart: writers write, erasers rub out and readers read.
- Writers: add a chemical mark such as a methyl group.
- Erasers: remove the mark, so epigenetic states can in principle be reversed.
- Readers: bind the marked site and recruit other proteins.
Why the other options are incorrect
- B. Writers add marks, erasers remove them and readers bind marked sites but do not recruit any partners: This gives readers the correct binding site but wrongly says they do not recruit partners. The defining reader role is to bridge the mark to complexes that open or compact chromatin, so denying recruitment makes it incomplete. Your answer
- C. Writers add marks, erasers remove them and readers bind DNA sequences and alter them: This says readers bind and alter DNA sequences, but readers bind chemical marks and leave the DNA sequence unchanged. Altering the sequence would be a mutation, not epigenetic reading. Your answer
- D. Writers add marks, erasers remove them and readers bind unmarked DNA sequences and recruit partners: This makes the first two roles correct, but readers bind the chemical mark rather than unmarked DNA sequence. A protein that binds unmarked DNA and recruits partners is acting as a sequence-specific transcription factor, not an epigenetic reader. Your answer
- E. Writers add marks, erasers remove them and readers bind marked sites and remove them: This says readers remove the marks they bind, which is the eraser role, not the reader role. Readers interpret the mark and recruit partners; they do not rub the mark off. Your answer
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