Question about the mutagens in DNA

Question

sme mutagens cause genetic changes which can be "corrected" by reexposing cells to the same mutagen. other mutagens do not behave in this way. provide one example of each of these two types of agents and describe the mutational changes cause in DNA. explain why some mutagens behave in one way while others do not.

Answer 1

This sounds like it is trying to get you to explain that mutagens that cause point mutations could cause another point mutation that brings them back to the orginial DNA when rexposed to the mutagen. But that is quite wrong, since point mutations arise randomly in the DNA. This question doesn't seem possibly/correct.

Answer 2

Some mutagens can indeed 'reverse' the effect of an initial exposure. Base analogs, such as 5-bromo-uracil, can cause both AT->GC mutations, but also GC->AT. So, an initial exposure could cause a mutation in one direction which could be reversed by a second mutation. In the same way, chemicals that cause frameshift mutations can do so by either adding or deleting a base. So an addition can be corrected by a second exposure that causes a deletion. In both cases the odds of a reversal are very small but in a large enough population you will find some examples.

Non-reversible mutations tend to be due to base modifiers, which create changes only in one direction, but not in the other. In these cases a second exposure cannot repair the damage. In a similar way, mutations due to large scale additions/deletions are unlikely to be reversed.