#$2.$ MC$1$R gene encodes a protein that has the function of embedding in the membrane of cells that are involved in skin or hair pigment production. MC$1$R is a signaling protein which can trigger the expression of other genes that control pigmentation.

Why does a "loss of function allele" for MC$1$R cause a change in coat color in dogs, cows and rabbits?

A$.$ The mutant allele either cannot be expressed to make the protein at all or the protein encoded now has a change in structure and a change in function.

B$.$ The new mutant allele loses it's signaling function and becomes instead an enzyme that creates the new pigment colors.

C$.$ The sequence of DNA nucleotides making up the MC$1$R gene has a darker color than DNA sequence of nucleotides that make up the mutant allele.

D$.$ All of the above a correct answers