CHROMOSOMAL VARIATION, SEGREGATION AND SEX DETERMINATION IN HYDROTAEA-MERIDIONALIS (DIPTERA, MUSCIDAE)

In addition to five pairs of euchromatic chromosomes common to all ind ividuals, three different morphological types of heterochromatic chrom osomes were found in Hydrotaea meridionalis: two acrocentric chromosom es of different length and a smaller submetacentric chromosome that oc cur in different combinations. The most common type, the larger of the acrocentric chromosomes, occurred as a pair in 149 out of 197 larvae. Mother-offspring combinations revealed that the larvae progeny of sev eral mothers carried morphologically only the common karyotype. Despit e existing morphological variation in karyotypes the same karyotypes w ere found in male and female adult flies. This observation is interpre ted by an autosomal sex-determining mechanism. As there was also found a sex-specific karyotype in males, a simple hypothesis to explain the observed distribution of karyotypes among sexes is suggested: one mal e locus located on one of the autosomes with a dominant heterogametic sex determination mechanism. Only in homozygous recessives for that lo cus is sex determined by the independent XX/XY sex-determining system.