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 semicolon should be used instead. A comma splice should not be confused, though, with asyndeton, a literary device used for a specific effect in which coordinating conjunctions are purposely omitted. Commas are always used to set off certain adverbs at the beginning of a sentence, including "however", "in fact", "therefore", "nevertheless", "moreover", "furthermore", and "still". If these adverbs appear in the middle of a sentence, they are followed and preceded by a comma. As in the second of the two below examples, if the two sentences are separated by a semicolon and the second sentence starts with an adverb, then