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 an imperative, as in: The above guidance is not universally accepted or applied. Long coordinating clauses are nonetheless usually separated by commas: In some languages, such as German and Polish, stricter rules apply on comma usage between clauses, with dependent clauses always being set off with commas, and commas being generally proscribed before certain coordinating conjunctions. The joining of two independent sentences with a comma and no conjunction (as in "It is nearly half past five, we cannot reach town before dark.") is known as a comma splice and is sometimes considered an error in English; in most cases a