By process of elimination you can deduce the answer: A mutation causing uncontrolled cell division in human tissue cells is cancer and definitely not beneficial. A mutation resulting in partial or complete loss of chlorophyll pigments in plants will lead to a plant not being able to photosynthesise and therefore unable to respire leading to death. A mutation resulting in a squirrel being born without ovaries means the squirrel will be unable to reproduce and there for is not beneficial. The answer is therefore a mutation inhibiting human immunodeficiency virus from entering the host cell. This means that the person who has this gene is unable to contract HIV which is beneficial
