[Genetic control of isolating mechanisms in the genus Drosophila]. / Geneticheskii kontrol' izoliruiushchikh mekhanizmov v rode Drosophila.

Published data on the genetic control of isolating mechanisms in the genus Drosophila are discussed. The main isolation types of genetic mechanisms (ecological isolation, behavioral isolation, hybrid sterility, and the inviability or impaired development of interspecific hybrids) are considered. It is shown that each of the isolation barriers between different species is controlled by a small number of genes. However, as each pair of sibling species is usually separated by several barriers, the total number of isolation genes is about 20 to 30. The probable sequence of events in the appearance of isolation barriers during the divergence of novel species is discussed. A concept of the consolidation of a new species is proposed. This concept is based on the assumption of the genetic determination of behavior that promotes crossing between individuals of the new genotype and constrains their crosses with individuals of the ancestral genotype.

[An electron microscopic study of the structure of the spermatozoa from sterile males from a crossing of Drosophila virilis x Drosophila lummei]. / Elektronno-mikroskopicheskoe issledovanie struktury spermatozoidov u steril'nykh samtsov ot skreshchivaniia Drosophila virilis x Drosophila lummei.

Using electron microscope, we have studied structure of the tail region of developing spermatozoa in sterile hybrid males FB1 and F2 resulting from D. virilis x D. lummei crosses, as well as in fertile males of D. virilis. Multiple disturbances in the structure of spermatid plasma membrane have been found in sterile males. The membrane is interrupted in many points; this is particularly apparent in the outer thicker layer. The adjacent nucleus (AN) of spermatids of hybrids also differs from that in D. virilis spermatid. The crystalline ultrastructure in this case has a lower volume as compared with D. virilis, it is located asymmetrically within the AN and is displaced to the edge of that part of the AN, which is located closely to the bundle of contractile fibrils. At the stage of elongation, nonuniform inclusions of irregular shape, several times larger than globules of the crystalline structure, are located nonuniformly within this crystal-like structure. The membrane of the AN is interrupted in many points or is fully absent. Matrix consisting of a large number of small globules is distributed nonuniformly within the AN. It is concluded that the presence of multiple disturbances of spermatid ultra-structure is the main factor leading to lack of sperm mobility and, correspondingly, sterility of virilis-lummei hybrid males.

[Genomic incompatibility in Drosophila virilis Sturt. X Drosophila lummei Hackman hybrids]. / Genomnaia nesovmestimost' u gibridov Drosophila virilis X Drosophila lummei Hackman.

Genetic analysis of male sterility in Drosophila virilis x D. lummei hybrids was performed. It was shown that hybrid male sterility was caused mainly by incompatibility of sex chromosomes X and Y and homozygous chromosome 2 of D. virilis with other autosomes of D. lummei. Genes of chromosomes 3 and 5 enhanced sterility whereas genes of chromosome 4 suppressed its development. Factors controlling hybrid male sterility were demonstrated to have a recessive type of inheritance. At 17 degrees C, chromosome 6 of D. lummei was eliminated in F1 hybrids of the cross female D. virilis x male D. lummei. At 17 degrees C and 25 degrees C, sterility of the F1 hybrid males was 96% and 9%, respectively. Thus, two isolation mechanisms-elimination of chromosome 6 and male sterility-can simultaneously operate in F1. In addition to the region of the species-specific inversion In 1(a+b), factors controlling male sterility were mapped to the vermillion region of the X chromosome.