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 used to separate clauses. In English, a comma is used to separate a dependent clause from the independent clause if the dependent clause comes first: "After I fed the cat, I brushed my clothes." (Compare this with "I brushed my clothes after I fed the cat.") A relative clause takes commas if it is non-restrictive, as in "I cut down all the trees, which were over six feet tall." (Without the comma, this would mean that only those trees over six feet tall were cut down.) Some style guides prescribe that two independent clauses joined by a coordinating conjunction ("for",