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Genome size or C-value is defined as the total amount of DNA contained within a haploid chromosome set and is regarded as a species-specific constant. Speciation among neotropical primates seems to be accompanied by marked quantitative changes in DNA content. A direct correlation between genome size and the presence of heterochromatin has also been proposed. In this work, we analyzed the genome of a female fertile hybrid between Cebus libidinosus and C. nigritus using interspecies comparative genomic hybridization (iCGH), in order to detect quantitative differences between the hybrid and the parental genomes. We also estimated the genome sizes of C. libidinosus and C. nigritus. Both species, considered subspecies of C. apella until 2001, have a highly homologous karyotype but are easily distinguishable at the chromosomal level due to the noncentromeric heterochromatin block on C. libidinosus chromosome 11. Our findings on C-value quantification support the species status for C. libidinosus and C. nigritus, each having a different genome size. The iCGH analysis of the hybrid revealed quantitative differences in comparison to both parental species. The hybrid genome contains a greater amount of DNA in the heterochromatic blocks related to those in the genomes of both parental species. In view of observations in previous and the present work, some hypotheses about genome dynamics of neotropical primates are proposed and discussed., (Copyright © 2011 S. Karger AG, Basel.)

Primate genomes show a great karyological variability while the DNA content variation is scarce. The biggest genome size occurs in Cercophitecus cephus (Catarrhini, Cercophitecidae) with 5.26 pg whereas the smallest one is described for Callicebus torquatus (Platyrrhini, Callithricidae) with 2.26 pg. Over the last 20 years different authors have been studying the Platyrrhini genomes on a chromosomal level. Among them, Cebus (Cebidae) being considered the most ancestral and conserved karyotype in relation to human karyotype has been extensively studied. Cebus genome sizes range from 3.40 to 3.98 pg. The species that inhabit Argentina, where they reach the most southern natural distribution, Cebus paraguayanus (CPA) and Cebus nigritus (CNI), have been extensively studied with classical cytogenetic comparisons focusing on banding pattern behavior. In the present study we performed comparative genomic hybridization (CGH) between these two closely related species with the aim of going a step further in the dissection of Cebus genomes. CGH evidenced that the DNA imbalances between them involved different genome regions, i.e. preferentially repetitive DNA in CPA and coding or very disperse DNA in CNI. Particularly, CNI showed species-specific DNA in more than 9 chromosomal pairs with a red/green (r/g) ratio ranging from 1.7 to 4, meaning that CNI presents at least twice as much DNA than CPA in those chromosomal segments. CPA showed species-specific DNA in the telomeric region of at least 3 chromosomal pairs with an r/g ratio of 0.5. They also showed a DNA gain in the chromosomal pairs with extracentromeric heterochromatin. Our findings modify the widespread idea of considering the heterochromatin proportion as the only difference between CPA and CNI. In Cebus then, the diversification process could be mediated by little changes in DNA content accompanied by a euchromatin-heterochromatin interaction although maintaining a minimum proportion like the one observed in CNI., (2010 S. Karger AG, Basel.)

The concentration of evolutionary breakpoints in primate karyotypes in some particular regions or chromosome bands suggests that these chromosome regions are more prone to breakage. This is the first extensive comparative study which investigates a possible relationship of two genetic markers (intrachromosomal telomeric sequences [TTAGGG]n, [ITSs] and fragile sites [FSs]), which are implicated in the evolutionary process as well as in chromosome rearrangements. For this purpose, we have analyzed: (a) the cytogenetic expression of aphidicolin-induced FSs in Cebus apella and Cebus nigrivittatus (F. Cebidae, Platyrrhini) and Mandrillus sphinx (F. Cercopithecidae, Catarrhini), and (b) the intrachromosomal position of telomeric-like sequences by FISH with a synthetic (TTAGGG)n probe in C. apella chromosomes. The multinomial FSM statistical model allowed us to determinate 53 FSs in C. apella, 16 FSs in C. nigrivittatus and 50 FSs in M. sphinx. As expected, all telomeres hybridized with the probe, and 55 intrachromosomal loci were also detected in the Cebus apella karyotype. The chi(2) test indicates that the coincidence of the location of Cebus and Mandrillus FSs with the location of human FSs is significant (P < 0.005). Based on a comparative cytogenetic study among different primate species we have identified (or described) the chromosome bands in the karyotypes of Papionini and Cebus species implicated in evolutionary reorganizations. More than 80% of these evolutionary breakpoints are located in chromosome bands that express FSs and/or contain ITSs., (Copyright (c) 2005 S. Karger AG, Basel.)

In this paper an ancestral karyotype for primates, defining for the first time the ancestral chromosome morphology and the banding patterns, is proposed, and the ancestral syntenic chromosomal segments are identified in the human karyotype. The chromosomal bands that are boundaries of ancestral segments are identified. We have analyzed from data published in the literature 35 different primate species from 19 genera, using the order Scandentia, as well as other published mammalian species as out-groups, and propose an ancestral chromosome number of 2n = 54 for primates, which includes the following chromosomal forms: 1(a+c(1)), 1(b+c(2)), 2a, 2b, 3/21, 4, 5, 6, 7a, 7b, 8, 9, 10a, 10b, 11, 12a/22a, 12b/22b, 13, 14/15, 16a, 16b, 17, 18, 19a, 19b, 20 and X and Y. From this analysis, we have been able to point out the human chromosome bands more "prone" to breakage during the evolutionary pathways and/or pathology processes. We have observed that 89.09% of the human chromosome bands, which are boundaries for ancestral chromosome segments, contain common fragile sites and/or intrachromosomal telomeric-like sequences. A more in depth analysis of twelve different human chromosomes has allowed us to determine that 62.16% of the chromosomal bands implicated in inversions and 100% involved in fusions/fissions correspond to fragile sites, intrachromosomal telomeric-like sequences and/or bands significantly affected by X irradiation. In addition, 73% of the bands affected in pathological processes are co-localized in bands where fragile sites, intrachromosomal telomeric-like sequences, bands significantly affected by X irradiation and/or evolutionary chromosomal bands have been described. Our data also support the hypothesis that chromosomal breakages detected in pathological processes are not randomly distributed along the chromosomes, but rather concentrate in those important evolutionary chromosome bands which correspond to fragile sites and/or intrachromosomal telomeric-like sequences., (Copyright (c) 2005 S. Karger AG, Basel.)