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 "against" consistent use of the serial comma: Many sources are against both systematic use and systematic avoidance of the serial comma, making recommendations in a more nuanced way (see Usage and subsequent sections). The style that always uses the serial comma may be less likely to result in ambiguity. Consider this apocryphal book dedication: There is ambiguity about the writer's parentage, because "Ayn Rand and God" can be read as in apposition to "my parents", leading the reader to believe that the writer claims Ayn Rand and God are the parents. A comma before "and" removes the ambiguity: But lists