Are mutations a source of genetic variation?

Question

Here is a question from the book *SAT II Success Biology E/M* (where the SAT is the exam taken by the American high school students): > Which of the following statements is true about mutations? (A) Rates > tend to be very high in most populations. (B) generally lethal (C) > irreversible (D) Only certain gene locations are affected. (E) source > of genetic variation In my opinion, we can definitely eliminate A, B, and D. Then, I struggle between C and E since I think mutations are definitely a source of genetic variation but are **as well** generally irreversible (I've found evidence on different websites, including this http://hawaiireedlab.com/wpress/?p=154 where the author writes that only **some** mutations are reversible). In the end, I think I should have probably gone with E because C can be seen as having some exceptions. Then, here is the book explanation for this question: > **The correct answer is (C).** These recent conclusions about > mutations—recall that Darwin did not know of mutations—are all the > reverse of those listed in the choices, with the exception of choice > (C), the correct answer. Rates, in fact, tend to be below in > populations, mutations are generally not lethal, any gene location can > be affected, and they are felt to be the source of genetic variation. > Darwin felt over-production of offspring was the source of potential > variation. The answer is C here. However, I didn't particularly understand why E wasn't considered a correct answer. Could you please explain why C, and not E, is correct?

Answer 1

Mutations are sources of genetic variation, so E is definitely the correct answer. Unfortunately, it's not uncommon to find a few errors in test prep books :(

A mutation can most definitely be reversed. For example, you can have a 2nd point mutation in the same location that reverts a base back to the wildtype form.