Swallowtail butterfly tiger swallowtail), Y-linkage determines whether the females are either wild-type (yellow and black) or melanic (dark melanin replaces the yellow background). This genetic difference stems from the fact that melanism is controlled by a single gene, which controls the level of dopamine in the organism. The enzyme BAS, which assists dopamine in producing the yellow pigmentation, normally found on the wings' background, is suppressed. Without the pigmentation, the butterfly appears mostly black (the melanic form) and is a Batesian mimic of "Battus philenor", the pipevine swallowtail. There are also "Papilio glaucus" that are not wholly black; several possess an intermediate
Comma list of more than two elements. A comma used in such a position is variously called a serial comma, an Oxford comma, or a Harvard comma (after the Oxford University Press and Harvard University Press, both prominent advocates of this style). Such use of a comma sometimes prevents ambiguity: The serial comma does not eliminate all confusion. Consider the following sentence: As a rule of thumb, "The Guardian Style Guide" suggests that straightforward lists ("he ate ham, eggs and chips") do not need a comma before the final "and", but sometimes it can help the reader ("he ate cereal, kippers,