Researchers studying mice have found that in utero exposure to certain chemicals can cause genetically identical twins to have different-colored fur. This is best explained by the fact that genetically linked traits can be modified by?

epigenetic marks.

Explanation:

Attributes which are not directly regulated by the genetic code, including DNA methylation and covalent histone protein modification. Methyl, acetyl, ubiquitin, phosphate, poly (ADP) ribose and other biochemical groups may also be added to the latter.