Epistasis

====Epistasis is when some genes mask the effect of other genes. Epistatic gene interaction have 3 possible phenotypes. Some people call the these three phenotypes "The Domino Effect." They are called the domino effect because one cannot be shown unless the one before has been turned on, just like dominoes one cannot fall unless the one behind it has already fallen. An example of this would be the color of fur of a dog. One dog is brown, the other dog is black, and the other dog is white. The white dog is white because he has two recessive alleles (homozygous). This dog does not contain a certain pigment that the brown and black dog have. Lets label the missing pigment B so it would be (_ _,rr). Since the first two alleles are turned off that would might it impossible for the next gene to be shown. It does not matter if the first two alleles are dominant or recessive if they aren't turned on they will have no effect on the dog. The brown dog has an allele of (aaB_), the dog is colored because it has one dominant allele B, it is recessive for Gene A that decides if it's brown or black. The black dog is (A_B_) because he has a dominant gene A and gene B. All the dominoes have fallen. Unlike the brown dog which was recessive for gene A so it did not appear more, and the white dog which did not have the allele turned on therefore the pigment that gave it color could not appear. Epistasis could be thought of as the domino effect in order for a gene to appear one has to be turned on, same as dominoes in order for one domino to fall the one before has to be pushed.====