Crossing over does occur in males of Drosophila ananassae from natural populations

Spontaneous crossing over in males of Drosophila ananassae has been well demonstrated using F1 individuals from crosses between marker stocks and wild type strains. However, the question of its occurrence in males from natural populations remained open. Here we present the cytological evidence that crossing over does occur in males of D. ananassae from two Brazilian populations, sampled nearly 21 years apart, and in two recently sampled populations, one from Indonesia and one from Okinawa, Japan. Cytological analysis of meiosis in males collected from nature and in sons of females from the same population inseminated in nature revealed the presence of chiasmata, inversion chiasmata, and isosite chromosome breakages in the diplotene cells in all sampled populations. These data demonstrate that reciprocal and nonreciprocal exchanges and chromosome breakages, previously reported as related events of male crossing over, do occur at variable frequencies among males from natural populations.

Study on Chromosome Aberrations of Crosses Between 3E Disomic Addition Line and 2C Addition Line

Thinopyrum elongatum, a wild relative of wheat, can be used as an excellent source of disease and abiotic stresses resistance and carries several useful traits, which have been transferred into wheat by interspecific hybridization. The most effective method of transferring the profitable genes of Th. elongatum into wheat is to induce chromosome recombination by the gametocidal system. In this study, cross, backcross and selfcross were performed between Chinese Spring-Th. elongatum 3E disomic addition line and Chinese Spring-Ae. cylindrica gametocidal chromosome 2C disomic addition line, and the gametocidal chromosome would induce chromosome breakages and aberrations. The chromosome counts of somatic cell and the observation of PMCs metaphase were performed in F2, BC1F1and F1, F2plants, respectively, the results showed that the gametocidal chromosome was functioning during the formation of gametes. The gametocidal chromosome 2C induced segregation for spike type in F2and BC1F1plants. Thus, the gametocidal chromosome 2C was demonstrated to be effective on transferring Th. elongatum 3E chromosome into wheat.

Chiasmata and chromosome breakages are related to crossing over in Drosophila ananassae males

A cytogenetic analysis of male crossing over in Drosophila ananassae revealed that cytological exchanges resulted in genetic crossing over, and that chiasma frequency and the genetic recombination correlated positively in chromosomes 2 and 3. Furthermore, the frequency of chromosome breakages correlated positively with chiasma frequency. Paracentric inversion heterozygosity had no detectable influence on the chromosome pairing or exchange events within the inversion loop at meiosis. Scoring of the chiasma demonstrated that males homozygous for the previously mapped enhancers of male crossing over had low frequencies of chiasmata, whereas higher frequencies of chiasmata were observed in males heterozygous for enhancers. The results presented here indicate that the genetic factors controlling male crossing over are involved in the origin of chromosome breakages and in exchange events.

Specific chromosome breakage at meiosis in C-heterochromatin mutants of the grasshopper Euchorthippus pulvinatus

Three males of Euchorthippus pulvinatus gallicus (Acrididae, Orthoptera) were found to be heterozygous for an enlarged interstitial C-block on the megameric chromosome, which usually has only small C-bands. These individuals exhibited a syndrome of chromosome breakages during the first meiotic division, the presence of the mutant C-bands being associated with the formation of specific weak points, as well as to an increase in sister chromatid cohesiveness. The pattern of breakage observed depends on the location of chiasmata relative to that of weak points and the enlarged C-block.Key words: C-heterochromatin mutant, chromosome breakage, weak point, sister chromatid cohesiveness.