The physical ends of mammalian and other vertebrate chromosomes consist of tandemly repeated (TTAGGG)(n) hexamers, nucleating a specialized telomeric structure. However, (TTAGGG)(n) sequences can also occur at non-telomeric sites, providing important insights into karyotypic evolution. By fluorescence in situ hybridization (FISH) we studied the chromosomal distribution of (TTAGGG)(n) sequences in 16 bird species, representing seven different orders. Many species, in particular the ratites, display (TTAGGG)(n) hybridization signals in interstitial and centromeric regions of their macrochromosomes in addition to the typical telomeric signals. In some but not all species these non-telomeric sites coincide with C-band-positive heterochromatin. The retention and/or amplification of telomeric (TTAGGG)(n) repeats at interstitial and centromeric sites may indicate the fusion of ancestral chromosomes. Compared with the macrochromosomes, the microchromosomes of most species are enriched with (TTAGGG)(n) sequences, displaying heterogeneous hybridization patterns. We propose that this high density of (TTAGGG)(n) repeats contributes to the exceptionally high meiotic recombination rate of avian microchromosomes.

In a Zoo-FISH study chicken autosomal chromosome paints 1 to 9 (GGA1–GGA9) were hybridized to metaphase spreads of nine diverse birds belonging to primitive and modern orders. This comparative approach allows tracing of chromosomal rearrangements that occurred during bird evolution. Striking homologies in the chromosomes of the different species were noted, indicating a high degree of evolutionary conservation in avian karyotypes. In two species, the quail and the goose, all chicken paints specifically labeled their corresponding chromosomes. In three pheasant species as well as in the American rhea and blackbird, GGA4 hybridized to chromosome 4 and additionally to a single pair of microchromosomes. Furthermore, in the pheasants fission of the ancestral galliform chromosome 2 could be documented. Hybridization of various chicken probes to two different chromosomes or to only the short or long chromosome arm of one chromosome pair in the species representing the orders Passeriformes, Strigiformes, and Columbiformes revealed translocations and chromosome fissions during species radiation. Thus comparative analysis with chicken chromosome-specific painting probes proves to be a rapid and comprehensive approach to elucidate the chromosomal relationships of the extant birds.

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A 15-year cytogenetic survey on one population of the leaf litter frog Eleutherodactylus maussi in northern Venezuela confirmed the existence of multiple XXAA♂/XAA^Y♀ sex chromosomes which originated by a centric (Robertsonian) fusion between the original Y chromosome and an autosome. 95% of the male individuals in this population are carriers of this Y-autosome fusion. In male meiosis the XAA^Y sex chromosomes pair in the expected trivalent configuration. In the same population, 5% of the male animals still possess the original, free XY sex chromosomes. In a second population of E. maussi analyzed, all male specimens are characterized by these ancestral XY chromosomes which form normal bivalents in meiosis. E. maussi apparently represents the first vertebrate species discovered in which a derived Y-autosome fusion still coexists with the ancestral free XY sex chromosomes. The free XY sex chromosomes, as well as the multiple XA^Y sex chromosomes are still in a very primitive (homomorphic) stage of differentiation. With no banding technique applied it is possible to distinguish the Y from the X. DNA flow cytometric measurements show that the genome of E. maussi is among the largest in the anuran family Leptodactylidae. The present study also supplies further data on differential chromosome banding and fluorescence in situ hybridization experiments in this amphibian species.

The aim of the study was to find out whether the estimation of the baseline ovarian volume prior to stimulation would be a suitable predictor for the risk of ovarian hyperstimulation syndrome (OHSS). A total of 101 patients underwent in-vitro fertilization (IVF) and embryo transfer. They had a 3-D volumetric assessment of the ovaries and body weight estimations on the first day of hormonal stimulation. A second measurement was performed on the day of ovulation induction with human chorionic gonadotrophin (HCG) together with an oestradiol 17 beta estimation in serum. During the IVF programme 15 women developed OHSS and 86 did not. There was a significant correlation between the baseline ovarian volume and subsequent occurrence of OHSS (P = 0.03). Other significant relationships were found between the occurrence of OHSS and the number of follicles (P = 0.002), the number of oocytes retrieved (P = 0.0001) and the length of the cycle (P = 0.0001). The body weight before and after the stimulation was significantly lower in the group of women who did develop the syndrome (P = 0.011 resp. 0.03). The oestradiol 17 beta concentration on the day of HCG administration in the serum of the patients who had OHSS was significantly higher (P = 0.0001). In conclusion, volumetry of the ovaries could help to detect patients at risk and prevent the occurrence of OHSS by early adjustment of the hormonal dosage. Recent advances in ultrasound technology (3-D ultrasound) enable quick and highly accurate volumetric assessments. Furthermore, our study confirms previous observations that low body weight and long cycles seem to be additional risk factors for the development of OHSS.