Die Speicheldrüsenchromosomen der StechmückeCulex Pipiens L. IV. Der Chromosomale Geschlechtsdimorphismus

In the salivary gland chromosomes of the mosquitoCulex pipiens L. band 10 C 3 of the small chromosome I in female larvae always shows a homozygous heterochromatic balloon, while male larvae are heterozygous for this structure, the homologous band being euchromatic. In males, heterozygous for a male-linked reciprocal translocation, the chromosome with the distinct euchromatic band is always involved in the segmental interchange with an autosome. It is concluded that the euchromatic state of band 10 C 3 represents the male-determining allelomorph, and the heterochromatic state the female-determining allelomorph (M and m, respectively). C. pipiens thus appears to be an excellent example of diplogenotypic determination of sex where the sexes are different in one pair of allelomorphs only. At the chromosomal level, this sexual dimorphism is expressed as a heterochromatic versus an euchromatic state of a single band. The significance of this observation is discussed in connection with the problem of the evolution of sex-determining mechanisms within the Nematocera.