The Y-Chromosomal and Autosomal Male-Determining M Factors of Musca Domestica Are Equivalent

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RESUMO

In Musca domestica, male sex is determined by a dominant factor, M, located either on the Y, the X or on an autosome. M prevents the activity of the female-determining gene F. In the absence of M, F becomes active and dictates female development. The various M factors may represent translocated copies of an ancestral Y-chromosomal M. Double mutants and germ line chimeras show that M(Y), M(I), M(II), M(III) and M(V) perform equivalent functions. When brought into the female germ line, they predetermine male development of the offspring. This maternal effect is overruled by the dominant female-determining factor F(D). M(I) and M(II) are weak M factors, as demonstrated by the presence of yolk proteins in M(I)/+ males and by the occurrence of some intersexes among the offspring that developed from transplanted M(I)/+ and M(II)/+ pole cells. The arrhenogenic mutation Ag has its focus in the female germ line and its temperature-sensitive period during oogenesis. We propose that M(I) and Ag represent allelic M factors that are affected in their expression. Analysis of mosaic gonads showed that in M. domestica the sex of the germ line is determined by inductive signals from the surrounding soma. We present a model to account for the observed phenomena.

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