Question

Why don't some mutations to a DNA sequence have a significant effect on phenotypic expression?

Answer 1

If you observe the universal genetic code chart you'll see that several codons represent the same protein. there are a total of \(4^{3}\) combinations whereas they code for (if I remember correctly) just 23 proteins for instance the codons representing leucine are `UUA`, `UUG`, `CUU`, `CUA`, `CUC` and `CUG`

Having said that, now if there was a point mutation in, say, `UUA` and it turned into `CUA` in effect it is still coding for a different variation of the same protein. the important part is that it is still the same amino acid, so there won't be any adverse effect just variation.

Did that make any sense to you?