Conserved regions of homologous G-banded chromosomes between orders in mammalian evolution: carnivores and primates.

Abstract

The recent derivation ofa biochemical map of33 loci of the domestic cat (Felis cattu) revealed a striking conservation of chromosomal linkage associations between the cat and humans. A comparison of homologous (by linkage criteria) chromosomes by using conventionally extended and high-resolution Gbanding of human and feline chromosomes is presented. Four criteria for establishing probable cytogenetic homologies of chromosomal regions were invoked: (i) map placement of homologous genes to the same chromosomes; (ii) cytological correlation of Gbanding pattern; (iii) placement of homologous genes, by regional gene mapping, in the region of cytological homology; and (iv) a requirement that the putative region of homology be ancestral and evolutionarily conserved within their respective orders. Five subchromosomal regions (homologous to human chromosome ip, 2p, 2q, 12, and X) were found to be conserved and homologous by all the stated criteria. The conserved regions constitute nearly 20% by length of the human chromosomal genome. The implications of conservation of chromosome homologies between mammalian orders whose last common ancestor became extinct more than 60 million years ago is discussed.The increasing application ofchromosome banding methods to cytogenetic studies of mammalian chromosomes has made it possible to monitor more accurately the divergence of chromosome structure over tens of millions of years of mammalian evolution (1)(2)(3). By using the pattern of banding as a guide, homologous regions in the chromosomes of two species can often be identified even when the overall morphologies of the chromosomes are quite different. While the chromosomes of nearly all major mammalian taxa have been investigated with modern banding procedures, phylogenetic chromosome relationships have been extensively studied in the primates and carnivores with particular attention to the Felidae family (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14).The elegant analyses of primate phylogenies presented by Dutrillaux and co-workers have established the feasibility of tracking the cytogenetic rearrangements that have occurred during the development of the primate order (1,(4)(5)(6)(7)(8)(9)(10). More recent studies using high-resolution banding techniques have shown that extensive chromosome banding homology exists not only between closely related primates (e.g., human, chimpanzee, gorilla, and orangutan) but also to a lesser extent between distantly related primates such as man and woolly monkey or lemur (6,7,9). Comparative cytological analyses of more than 70 extant primate species has permitted the reconstruction of more than 150 chromosome rearrangements (robertsonian translocations, paracentric and pericentric inversions, acrocentric fusions, and metacentric chromosome fissions) that presumably occurred during the 60-80 million years of primate evolution. The chromosome homologies have been further extended in the primates by comparative gene mapping of homologous enzyme structural genes using somatic cell hybrids...

Phylogenetic implications of the 38 putative ancestral chromosome segments for four canid species

“…Comparative analysis of hybridization patterns of dog probes among these four canids, between canids and cats, and between canids and humans strongly supports the fission hypothesis. Previous comparative genomics have demonstrated that the karyotypes of domestic cats (2n = 38) and, to a lesser extent, humans (2n = 46), closely resemble the ancestral karyotype of all mammals, including the carnivores (Nash and O'Brien, 1982;Dutrillaux and Couturier, 1983;Frönicke et al, 1997;Hameister et al, 1997;O'Brien et al, 1997;Wienberg et al, 1997). It follows that the karyotype of the most recent common ancestor of extant canids must have diverged from a low-diploid number karyotype similar to that of the present-day cat.…”

Extensive Conservation of Sex Chromosome Organization Between Cat and Human Revealed by Parallel Radiation Hybrid Mapping

“…Whether this conservation of synteny translates to conservation of gene order is unclear, though preliminary studies indicate this may be the case (Murphy et al 1999). Cytogenetic studies have revealed considerable G-banding homology between cat and human X chromosomes, suggesting a high degree of colinearity between both chromosomes (Nash and O'Brien 1982).…”

Origins of primate chromosomes – as delineated by Zoo-FISH and alignments of human and mouse draft genome sequences

“…The first attempts to identify ancestral karyotypes were based on observations of similarities in chromosome banding patterns between distantly related species (Dutrillaux, 1979; Dutrillaux et al, 1980;Nash and O'Brien, 1982). These observations indicated the evolutionary conservation of several chromosomes, which could be corroborated for the karyotypes of cat and human by gene mapping data (Nash and O'Brien, 1982). However, only after fluorescence in situ hybridization (FISH) was introduced into comparative cytogenetics the suspected homologies could be proven for entire chromosomes and karyotypes.…”