Evolutionary conserved chromosomal segments in the human karyotype are bounded by unstable chromosome bands

Abstract

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+c₁), 1(b+c₂), 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.

Forty-eight new cases with infertility due to balanced chromosomal rearrangements: Detailed molecular cytogenetic analysis of the 90 involved breakpoints

“…Moreover, ITS and MTLE co-localize in parts with fragile sites (22)(23)26,(28)(29)(30). The latter are also reported to hold di-or tri-nucleotide repeats (31).…”

“…Mariner transposon-like elements (MTLE) (22) and intrachromosomal telomeric-like sequences (ITS) (23) are special subgroups of the recently reported segmental duplications (24), which were shown to be involved in primate evolution and also in cancer development (25)(26)(27). Moreover, ITS and MTLE co-localize in parts with fragile sites (22)(23)26,(28)(29)(30).…”

Are molecular cytogenetics and bioinformatics suggesting diverging models of ancestral mammalian genomes?

“…This problem is likely to be aggravated by the presence of mammalian genomic rearrangement hotspots. These have been identified by both bioinformatic and molecular cytogenetic methods (Murphy et al 2003;Bailey et al 2004;Ruiz-Herrera et al 2005). Clearly, the "reuse" of such breakpoint regions (Pevzner and Tesler 2003) complicates the tracing of rearrangements.…”

Hemiplasy and homoplasy in the karyotypic phylogenies of mammals

“…Standard wisdom is that each such syntenic block is of monophyletic origin, because the independent assembly of a shared synteny in different lineages seems mechanistically highly implausible (14). In other words, shared syntenic associations are much more useful in defining clades than chromosomal reorganizations that disrupt an ancestral synteny, because the latter might recur by means of breakpoint reuse (15)(16)(17)(18), especially in regions of segmental duplications (19), high concentrations of repetitive elements, and fragile sites (18,20,21). With respect to monophyletic origin (but not with respect to the probability of later evolutionary loss), the potential phylogenetic utility of syntenic blocks thus bears a considerable analogy to the phylogenetic utility of SINE elements, both of which are viewed as rare genomic changes (22).…”