“…ELECTROPHORETIC analyses of Drosophila extracts have revealed polymorphisms for many enzymes. The existence of electrophoretic variants makes possible the determination of the genetic locus of an enzyme (see Fox et al, 1971, for a summary of Drosophila enzyme map positions). CouRTRIGHT (1967) and SHAW (1969, 1970) have used electrophoretic enzyme variants to study the time of expression of paternal genes in hybrid flies.…”