A male-determining factor on autosome 1 and occurrence of male-recombination in the housefly, Musca domestica L..

Linkage analyses of sex-determining factors in a Fijian housefly strain, Suva Dump Fiji (SDF), were performed by using genetically marked autosomes. Although a Y chromosome could not be detected, the presence of at least three kinds of autosomal male-determining factors, IM, IIM and IIIM, was demonstrated in males of this strain. Both males and females of this strain carried the IIM-chromosome in the homozygous state. In addition, the females carried a fourth chromosomal female determining factor (F), which acts epistatically over the plural number of M factors.It is known that no crossing-over occurs in normal XY-type housefly males. However, XX males heterozygous for the IM-chromosome extracted from the SDF strain and a acv bp marker chromosome produced recombinants with very low frequency. These recombinants seemed to be the resultants of male crossing-over at the meiotic cell stage. On the basis of male-recombination data, the M factor on the first chromosome was mapped on the right side of bp locus.