Peculiarities of Meiosis in Drosophila: A Classical Object of Genetics Has Nonstandard Meiosis

Meiosis in Drosophila differs from the canonical type. Males lack synaptonemal complexes, chiasmata, and crossing-over. Only females have these classical traits of meiosis. However, during meiosis prophase I, female Drosophila lack the bouquet-like chromosome arrangement, an accessory mechanism for homologous chromosomes synapsis that is typical for the majority of eukaryotes. Instead, the pericentromeric heterochromatic regions of chromosomes are fused into the chromocenter. This leads to peculiarities in the pairing, synapsis, and segregation of chromosomes and to the so-called interchromosomal phenomena (effects). During late prophase I in females, chromosomes are packed in a karyosome, which is also characteristic of females in other animals with the nutrimental type of egg nutrition. The dissimilarities of meiosis in Drosophila from the classical scheme do not affect significantly its genetic consequences.