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 operator to how sequences of statements are enclosed in braces: codice_2 is a sequence of expressions, separated by commas, which evaluates to the last expression codice_3 while codice_4 is a sequence of statements, and does not evaluate to any value. A comma can only occur between two expressions – commas "separate" expressions – unlike the semicolon, which occurs at the end of a (non-block) statement – semicolons "terminate" statements. The comma operator has the lowest precedence of any C operator, and acts as a sequence point. In a combination of commas and semicolons, semicolons have lower precedence than commas, as semicolons