Why are most mutations neutral to slightly deleterious? A.Many mutations are likely to be neutral because of the high level of redundancy of the genetic code or because mutations occur in an area of DNA that does not affect protein coding or expression. B. Many mutations are likely to be slightly deleterious because of the similar properties of some amino acids that may only affect function slightly or because the mutation affects expression but not the protein itself. C. The phenotypic effect of many mutations depends on the environment that they occur in, so mutations can be neutral or only slightly affect fitness if the environment compensates for what would otherwise be a strong effect on fitness. D. All of the above.