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
Swallowtail butterfly species inhabit altitudes ranging from sea level to high mountains, as in the case of most species of "Parnassius". The majority of swallowtail species and the greatest diversity are found in the tropics and subtropical regions between 20°N and 20°S, particularly Southeast Asia, and between 20°N and 40°N in East Asia. Only 12 species are found in Europe and only one species, "Papilio machaon" is found in the British Isles. North America has 40 species, including several tropical species and "Parnassius". The northernmost swallowtail is the Siberian Apollo ("Parnassius arcticus"), found in the Arctic Circle in northeastern Yakutia, at altitudes