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
Serial comma to "The Oxford Companion to the English Language", "Commas are used to separate items in a list or sequence … Usage varies as to the inclusion of a comma before "and" in the last item … This practice is controversial and is known as the serial comma or Oxford comma, because it is part of the house style of Oxford University Press." Some use it only where necessary to avoid ambiguity, in contrast to such guides as "Garner's Modern American Usage", which advocate its routine use to avoid ambiguity. Common arguments "for" consistent use of the serial comma: Common arguments