Endosymbiotic bacteria can directly manipulate their host's sex determination towards the production of female offspring.

Sex‐determining mechanisms appear to be very diverse in invertebrates. Haplodiploidy is a widespread mode of reproduction in insects: males are haploid and females are diploid. Several models have been proposed for the genetic mechanisms of sex determination in haplodiploid Hymenoptera. Although a one‐locus multi‐allele model is valid for several species, sex determination in other species cannot be explained by any of the existing models. Evidence for and predictions of two recently proposed models are discussed. Some genetic and molecular approaches are (...) proposed to study sex determination in Hymenoptera. (shrink)

The mechanisms by which sex is genetically determined are bewilderingly diverse and appear to change rapidly during evolution.(1) What makes the sex‐determining process so prone to perturbations? Two recent articles(2,3) explore theoretically the role of genetic conflict in sex determination evolution. Both studies use the idea that selection on sex‐determining genes may act differently in parents and in offspring and they suggest that the resulting conflict can drive changes in sex‐determining mechanisms. BioEssays 23:477–480, 2001. © 2001 John Wiley & Sons, (...) Inc. (shrink)

The Y chromosomes of most Drosophila species are necessary for male fertility but they are not involved in sex determination. They have many puzzling properties that resemble the effects caused by B chromosomes. Classical genetic and molecular studies reveal substantial affinities between Y and B chromosomes and suggest that the Y chromosomes of Drosophila are not degenerated homologues of the X chromosomes, but rather that their Y chromosomes evolved as specialized supernumeraries similar to classical B chromosomes.