The ruby eye-color mutant in the house fly, Musca domestica L. A case of duplicate genes.

ruby eye-color mutant ( rb) in the house fly, Musca rEomestica L., was Tz@na l ly found by HIROYOSHI (1960) in the progeny of an “orange-eyed” stock collected in the field by L. D. ZINGRONE (Illinois State Natural History Survey, Urbana, Illinois, 1955). HIROYOSHI reported that the rb and ct (cut-wing tips) mutants were linked though the “results of all F, tests deviated significantly from expected segregation ratios, probably due to poor viability of the rb mutant, or the eyes of some prospective rb individuals might be normal when the larvae are reared in a mixed cu1t~u-e.’~ Thus he implied that a reduction in the rb class was responsible for the deviant ratios and that rb was the result of a single recessive gene. Evidence accumulated in this laboratory shows that the rb mutant phenotype results from the simultaneous expression of two recessive loci of two nonhomologous chromosomes (duplicate genes). Also, the ruby stock has been shown to contain the factor (s) giving holandric inheritance of one member of the third pair of autosomes (segregation of the third pair of autosomes is sex-determining) . The phenomenon of holandric dheritance of chromosome I11 was reported to arise spontaneously in native populations of house flies (MILANI and FRANCO 1959; SULLIVAN 1958, 1961 ; HIROYOSHI 1964; TSUKAMOTO, BABA, and HIRAGA 1961 ; KERR 1960). Normally, segregation of the X and Y chromosomes in the male is sex determining (females are X X ) .