A common feature of the majority of the genetic studies on ethanol behavior in Drosophila is the use of transformation vectors that contain a version of the white (w) gene as a selectable phenotypic marker (mini-w). The w gene product is an ABC transporter subunit thought to heterodimerize with the products of the brown and scarlet genes to form a functional transporter (Ewart and Howells, 1998; Mackenzie et al., 1999). White protein localizes to the endosome in pigment cells where it cooperates with Brown and Scarlet proteins to mediate the intracellular transport of guanine and tryptophan metabolites (Anaka et al., 2008; Mackenzie et al., 2000). Wild-type flies have red eyes, whereas null mutations in w lead to a complete loss of eye pigmentation (i.e. white eyes).
