No abstract

The aim of this study was to compare the rate of sperm DNA fragmentation (rSDF; increase of SDF over time) in fresh and gradient isolated frozen-thawed semen samples from male sperm donors of proven fertility. SDF was assessed in the two samples obtained from the same fifteen male donors after 0.5, 1.5, 4.5, 6, 24, 48, and 72 h of incubation in a humidified atmosphere of 5% CO 2 in air at 371C. Analysis was performed based on chromatin dispersion patterns evaluated using the Halosperms kit. No significant differences in SDF were obtained when fresh and gradient-isolated frozen-thawed spermatozoa were compared at baseline. However, the rSDF shown by the two samples differed and gradient-isolation selected for sperm subpopulations showing a lower variance for SDF. At the individual level, sperm selection by density gradient purification in frozen-thawed samples did not improve the levels of SDF when compared with the values obtained in fresh samples at baseline.

We evaluate for the first time the effect of Wolbachia infection, involving two different supergroups, on the structure and dynamics of the hybrid zone between two subspecies of Chorthippus parallelus (Orthoptera) in the Pyrenees. Wolbachia infection showed no effects on female fecundity or a slight increment in females infected by F supergroup, although in the last case it has to be well established. Cytoplasmic incompatibility (CI) is confirmed in crosses carried out in the field between individuals from a natural hybrid population. This CI, registered as the relative reduction in embryo production (s h ), was of s h = 0.355 and s h = 0.286 in unidirectional crosses involving B and F supergroups, respectively. CI also occurred in bidirectional crosses (s h = 0.147) but with a weaker intensity. The transmission rates of the two Wolbachia strains (B and F) were estimated by the optimization of a theoretical model to reach the infection frequencies observed in certain population. To fit this scenario, both supergroups should present transmission rates close to 1. Further, we have simulated the infection dynamics, and hence, the capacity of Wolbachia to structure the population of the host insects and to affect to reproduction and genetic introgression in the hybrid zone. This represents a first example of the influence of Wolbachia in an insect natural hybrid zone.

Studies during the last 20 years have shown that the chromosomes of many organisms, especially those of higher vertebrates, consist of a series of segments having different properties. These can be recognized as, for example, G- and R-bands. Recent studies have indicated that genes tend to lie in the R-bands rather than in the G-bands, although the number of genes that has been mapped with high precision is, as yet, only a very small proportion of the total, probably much less than 1%. We have therefore sought to study the distribution of genes on chromosomes using a cytological approach in conjunction with "universal" markers for genes. Such markers include mRNA and the gene-rich, G+C-rich H3 fraction of DNA, both of which can be localized using in situ hybridization, and DNase I hypersensitivity, and digestion by restriction enzymes known to show selectivity for the CpG islands associated with active genes, both of which can be detected using in situ nick translation. We have chosen to use the approaches involving in situ nick translation and have shown that the patterns of DNase I hypersensitivity and of CpG islands on human chromosomes show a strict correspondence to R-banding patterns: Deviations from R-banding patterns reported by previous investigators who have made similar studies appear to be attributable to excessive digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

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