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At least 703 records · Page 39Linked to original sources
PubMed2005

The evolutionary forces maintaining a wild polymorphism of Littorina saxatilis: model selection by computer simulations.

Two rocky shore ecotypes of Littorina saxatilis from north-west Spain live at different shore levels and habitats and have developed an incomplete reproductive isolation through size assortative mating. The system is regarded as an example of sympatric ecological speciation. Several experiments have indicated that different evolutionary forces (migration, assortative mating and habitat-dependent selection) play a role in maintaining the polymorphism. However, an assessment of the combined contributions of these forces supporting the observed pattern in the wild is absent. A model selection procedure using computer simulations was used to investigate the contribution of the different evolutionary forces towards the maintenance of the polymorphism. The agreement between alternative models and experimental estimates for a number of parameters was quantified by a least square method. The results of the analysis show that the fittest evolutionary model for the observed polymorphism is characterized by a high gene flow, intermediate-high reproductive isolation between ecotypes, and a moderate to strong selection against the nonresident ecotypes on each shore level. In addition, a substantial number of additive loci contributing to the selected trait and a narrow hybrid definition with respect to the phenotype are scenarios that better explain the polymorphism, whereas the ecotype fitnesses at the mid-shore, the level of phenotypic plasticity, and environmental effects are not key parameters.

Animals↗
PubMed2001

Phylogeography of the trumpetfishes (Aulostomus): ring species complex on a global scale.

The distribution of circumtropical marine species is limited by continental boundaries, cold temperate conditions, and oceanic expanses, but some of these barriers are permeable over evolutionary time scales. Sister taxa that evolved in separate ocean basins can come back into contact, and the consequences of this renewed sympatry may be a key to understanding evolutionary processes in marine organisms. The circumtropical trumpetfishes (Aulostomus) include a West Atlantic species (A. maculatus), an Indian-Pacific species (A. chinensis), and an East Atlantic species (A. strigosus) that may be the product of a recent invasion from the Indian Ocean. To resolve patterns of divergence and speciation, we surveyed 480 bp of mitochondrial DNA cytochrome b in 196 individuals from 16 locations. Based on a conventional molecular clock of 2% sequence divergence per million years, the deepest partitions in a neighbor-joining tree (d = 0.063-0.082) are consistent with separation of West Atlantic and Indian-Pacific species by the Isthmus of Panama, 3-4 million years ago. By the same criteria, trumpetfish in the East Atlantic were isolated from the Indian Ocean about 2.5 million years ago (d = 0.044-0.054), coincident with the advent of glacial cycles and cold-water upwelling around South Africa. Continental barriers between tropical oceans have only rarely been surmounted by trumpetfishes, but oceanic barriers do not appear to be substantial, as indicated by weak population partitioning (phiST = 0.093) in A. chinensis across the Indian and Pacific Oceans. Finally, morphological and mitochondrial DNA data indicate hybridization of A. strigosus and A. maculatus in Brazil. After 3-4 million years and a globe-spanning series of vicariant and dispersal events, trumpetfish lineages have come back into contact in the southwest Atlantic and appear to be merging. This ring species phenomenon may occur in a broad array of marine organisms, with clear implications for the production and maintenance of biodiversity in marine ecosystems.

Animals↗
PubMed2006

Insertion events of CR1 retrotransposable elements elucidate the phylogenetic branching order in galliform birds.

Using standard phylogenetic methods, it can be hard to resolve the order in which speciation events took place when new lineages evolved in the distant past and within a short time frame. As an example, phylogenies of galliform birds (including well-known species such as chicken, turkey, and quail) usually show low bootstrap support values at short internal branches, reflecting the rapid diversification of these birds in the Eocene. However, given the key role of chicken and related poultry species in agricultural, evolutionary, general biological and disease studies, it is important to know their internal relationships. Recently, insertion patterns of transposable elements such as long and short interspersed nuclear element markers have proved powerful in revealing branching orders of difficult phylogenies. Here we decipher the order of speciation events in a group of 27 galliform species based on insertion events of chicken repeat 1 (CR1) transposable elements. Forty-four CR1 marker loci were identified from the draft sequence of the chicken genome, and from turkey BAC clone sequence, and the presence or absence of markers across species was investigated via electrophoretic size separation of amplification products and subsequent confirmation by DNA sequencing. Thirty markers proved possible to type with electrophoresis of which 20 were phylogenetically informative. The distribution of these repeat elements supported a single homoplasy-free cladogram, which confirmed that megapodes, cracids, New World quail, and guinea fowl form outgroups to Phasianidae and that quails, pheasants, and partridges are each polyphyletic groups. Importantly, we show that chicken is an outgroup to turkey and quail, an observation which does not have significant support from previous DNA sequence- and DNA-DNA hybridization-based trees and has important implications for evolutionary studies based on sequence or karyotype data from galliforms. We discuss the potential and limitations of using a genome-based retrotransposon approach in resolving problematic phylogenies among birds.

Animals↗
PubMed2002

Late Quaternary distributional stasis in the submediterranean mountain plant Anthyllis montana L. (Fabaceae) inferred from ITS sequences and amplified fragment length polymorphism markers.

Anthyllis montana is a submediterranean, herbaceous plant of the southern and central European mountains. The internal transcribed spacer (ITS) regions of nuclear ribosomal DNA were sequenced from multiple accessions of the species and several closely related taxa. In addition, amplified fragment length polymorphism (AFLP) was analysed from 71 individuals of A. montana collected in 20 localities, mainly in the Pyrenees, Alps, Italian Peninsula and Balkans. Our ITS phylogeny showed a sequential branching pattern in A. montana, implying a western Mediterranean origin followed by an eastward migration. ITS clock calibrations suggest that speciation of A. montana took place at the Pliocene-Pleistocene boundary, while intraspecific divergence dates to Late Quaternary times (i.e. 0.7 million years ago). The AFLP analyses revealed a major genetic (west/east) subdivision within A. montana, probably caused by the massive glaciation of the Alps during this latter time period. The present-day absence of A. montana from vast parts of the Alps, which appear ecologically suitable for the species, together with the finding of evenly distributed AFLP variability within each of the two western and eastern lineages identified, is taken as evidence for a largely static Late Quaternary history without large-scale migration. High levels of AFLP variation observed among populations, together with weak or absent patterns of isolation by distance, seem to be in accord with long-term population insularization and distributional stasis. However, recent small-scale migration and a narrow hybrid zone between western and eastern lineages need to be postulated to explain the intermediate genetic composition of individuals from the Maritime Alps, a well-known suture-zone for other plant and animal species.

DNA, Ribosomal Spacer↗
PubMed2006

The impact of intragenic recombination on phylogenetic reconstruction at the sectional level in Eucalyptus when using a single copy nuclear gene (cinnamoyl CoA reductase).

Low copy number nuclear genes have been found to be useful for phylogenetic reconstruction at different taxonomic levels. This study investigated the utility of a single copy gene, cinnamoyl CoA reductase (CCR), for resolving phylogenetic relationships at the sectional level within Eucalyptus. The monophyly of sections Exsertaria and Latoangulatae was explored, using section Maidenaria as an outgroup, and the impact of intragenic recombination on phylogenetic reconstruction examined. Phylogenetic analysis did not resolve monophyletic groups. Latoangulatae and Maidenaria were polyphyletic or paraphyletic. Exsertaria species formed a clade but included a single Latoangulatae species (E. major). Recombination analysis identified two intragenic recombination events that involved species from different sections, which have probably been facilitated by inter-sectional hybridisation. One of the events most likely occurred prior to speciation, with several Latoangulatae species having the recombinant allele. The other event may have occurred after speciation, since only one of two E. globulus samples possessed the recombinant allele. This is the first detailed report of intragenic recombination in both CCR and Eucalyptus, and between species of different sections of a plant genus. The occurrence of intragenic recombination may explain the anomalous positions of some species within the phylogenetic tree, and indicates that phylogenetic analysis of Eucalyptus using nuclear genes will be problematic unless recombination is taken into account.

Aldehyde Oxidoreductases↗
PubMed2002

Structure and evolution of the Smith-Magenis syndrome repeat gene clusters, SMS-REPs.

An approximately 4-Mb genomic segment on chromosome 17p11.2, commonly deleted in patients with the Smith-Magenis syndrome (SMS) and duplicated in patients with dup(17)(p11.2p11.2) syndrome, is flanked by large, complex low-copy repeats (LCRs), termed proximal and distal SMS-REP. A third copy, the middle SMS-REP, is located between them. SMS-REPs are believed to mediate nonallelic homologous recombination, resulting in both SMS deletions and reciprocal duplications. To delineate the genomic structure and evolutionary origin of SMS-REPs, we constructed a bacterial artificial chromosome/P1 artificial chromosome contig spanning the entire SMS region, including the SMS-REPs, determined its genomic sequence, and used fluorescence in situ hybridization to study the evolution of SMS-REP in several primate species. Our analysis shows that both the proximal SMS-REP (approximately 256 kb) and the distal copy (approximately 176 kb) are located in the same orientation and derived from a progenitor copy, whereas the middle SMS-REP (approximately 241 kb) is inverted and appears to have been derived from the proximal copy. The SMS-REP LCRs are highly homologous (>98%) and contain at least 14 genes/pseudogenes each. SMS-REPs are not present in mice and were duplicated after the divergence of New World monkeys from pre-monkeys approximately 40-65 million years ago. Our findings potentially explain why the vast majority of SMS deletions and dup(17)(p11.2p11.2) occur at proximal and distal SMS-REPs and further support previous observations that higher-order genomic architecture involving LCRs arose recently during primate speciation and may predispose the human genome to both meiotic and mitotic rearrangements.

Abnormalities, Multiple↗
PubMed1993

Recent stable insertion of mitochondrial DNA into an Arabidopsis polyubiquitin gene by nonhomologous recombination.

Sequence analysis of a newly identified polyubiquitin gene (UBQ13) from the Columbia ecotype of Arabidopsis thaliana revealed that the gene contained a 3.9-kb insertion in the coding region. All subclones of the 3.9-kb insert hybridized to isolated mitochondrial DNA. The insert was found to consist of at least two, possibly three, distinct DNA segments from the mitochondrial genome. A 590-bp region of the insert is nearly identical to the Arabidopsis mitochondrial nad1 gene. UBQ13 restriction fragments in total cellular DNA from ecotypes Ler, No-0, Be-0, WS, and RLD were identified and, with the exception of Be-0, their sizes were equivalent to that predicted from the corresponding ecotype Columbia UBQ13 restriction fragment without the mitochondrial insert. Isolation by polymerase chain reaction and sequence determination of UBQ13 sequences from the other ecotypes showed that all lacked the mitochondrial insert. All ecotypes examined, except Columbia, contain intact open reading frames in the region of the insert, including four ubiquitin codons which Columbia lacks. This indicates that the mitochondrial DNA in UBQ13 in ecotype Columbia is the result of an integration event that occurred after speciation of Arabidopsis rather than a deletion event that occurred in all ecotypes except Columbia. This stable movement of mitochondrial DNA to the nucleus is so recent that there are few nucleotide changes subsequent to the transfer event. This allows for precise analysis of the sequences involved and elucidation of the possible mechanism. The presence of intron sequences in the transferred nucleic acid indicates that DNA was the transfer intermediate. The lack of sequence identity between the integrating sequence and the target site, represented by the other Arabidopsis ecotypes, suggests that integration occurred via nonhomologus recombination. This nuclear/organellar gene transfer event is strikingly similar to the experimentally accessible process of nuclear integration of introduced heterologous DNA.

Amino Acid Sequence↗
PubMed1998

Recent studies on the reproductive biology of the schistosomes and their relevance to speciation in the Digenea.

The members of the family Schistosomatidae, dioecious Digenea, are discussed with regard to their distribution, intermediate and definitive host-parasite relationships. The biological species concept is considered together with the difficulties of its application to Schistosoma spp. and the Digenea. The correlation between pairing of adult schistosomes, physical and sexual development and the maintenance of reproductive potential is emphasised. Development of the female reproductive system does not depend upon species-specific pairing. In some combinations, e.g., Schistosoma haematobium/Schistosoma intercalatum and Schistosoma bovis/Schistosoma curassoni, a specific mate choice system apparently does not exist, whereas it does in other combinations, e.g., Schistosoma mansoni/Schistosoma intercalatum. In mixed infections change of mate may occur and when the opportunity arises heterospecific pairs of worms will change partners to conspecific pairs. Interspecific pairing in adult schistosomes will lead to either hybridisation or parthenogenesis. Yet the majority of schistosomes that inhabit the same definitive host maintain their genetic identity: specific mate recognition, site selection within the host and heterologous immunity have been suggested as isolating mechanisms. Experimental intraspecific crosses have enabled evaluation of the degree to which some populations separated and became reproductively isolated through pre-mating isolating mechanisms, indicative of incipient speciation, e.g., the Lower Guinea and Zaire strains of S. intercalatum. The occurrence and significance of parthenogenesis in schistosomes and other species of Digenea are discussed. The consequences of interspecific mating interactions in schistosomes with regard to parasite epidemiology, interspecific competition and genetic heterogeneity are debated. Geographical isolation and host specificity represent important pre-zygotic isolating mechanisms. It is suggested that site selection within the host and heterologous immunity may both reduce interspecific genetic interchange when digenean parasites utilise the same definitive host.

Animals↗
PubMed1985

The I region of the C57BL/10 mouse: characterization and physical linkage to H-2K of an SB beta-like class II pseudogene, psi A beta 3.

In the C57BL/10 mouse, 140 kilobases (kb) of the I region (I-Ab, I-Eb) were isolated as recombinant cosmids. The class II genes A beta 2, A beta 1, A alpha,E beta 1, E beta 2, and E alpha are located from centromere to telomere in a region of approximately equal to 110 kb, which shows that the I region in the b haplotype has a similar overall organization to those described for the d, k, and wr7 haplotypes. In addition to these genes, we have also isolated a class II gene, psi A beta 3, which is physically linked to the class I H-2K region, 75 kb telomeric to the H-2Kb gene. This orients the H-2K region on the genetic map with the H-2Kb gene being located toward the I region. The sequence of the beta 2 domain of psi A beta 3 is similar to the immunoglobulin-like domain of other class II genes. Interestingly, it shows 83% nucleotide homology to the human SB beta gene, the same homology that was seen previously between the immunoglobulin-like exons of A beta 1 and DC beta and between E beta 1 and DR beta, respectively. It is likely, therefore, that psi A beta 3 represents a member of a third SB-like class II gene family present in addition to I-A and I-E genes and that the divergence of the SB family predates the speciation of rodents and primates. Comparison of the DNA sequence of the exon encoding the beta 2 domain of psi A beta 3 in the b or k haplotypes with functional class II genes shows that a deletion of eight nucleotides has occurred, such that the psi A beta 3 sequence cannot be translated into a functional class II protein. This suggests that psi A beta 3 is a pseudogene.

Alleles↗
PubMed2003

Evolution in Darwin's finches: a review of a study on Isla Daphne Major in the Galápagos archipelago.

This paper reviews research pertaining to the problem of speciation of the finches on the Galápagos archipelago carried out by assistants, several colleagues, Peter Grant and myself. I give a brief history of the radiation, examine the process of divergence by natural selection over time, and then consider the nature of the reproductive barrier to gene flow between closely related species. Fluctuating climatic conditions have produced a continuously changing ecological landscape and altered feeding conditions for the finches over the last 30 years. Finch populations tracked these changes by natural selection and evolutionary responses to the main events. At each event significant morphological change occurred from one generation to the next generation. As a consequence of these accumulated changes, the mean bill shape and body size of the Geospiza fortis and G. scandens populations differed markedly from 1973 to 2002. Song, a learned culturally transmitted trait, acted as a barrier to reproduction between these species. Rare incidences of misimprinting on song led to hybridization and introgression. Low levels of gene flow from one species to another increased genetic variation on which selection acted. Although the major driving force of diversification was ecological change, the process of diversification involved a subtle interplay between ecology, genetic evolution and learned culturally transmitted traits. An important message for conservation is that neither the environment nor species are fixed entities, therefore a wise strategy for conserving endangered species should keep them capable of further change.

Journal Article↗
PubMed2001

The nonA gene in Drosophila conveys species-specific behavioral characteristics.

The molecular basis of species-specific differences in courtship behavior, a critical factor in preserving species boundaries, is poorly understood. Genetic analysis of all but the most closely related species is usually impossible, given the inviability of hybrids. We have therefore applied interspecific transformation of a single candidate behavioral locus, no-on-transient A (nonA), between Drosophila virilis and D. melanogaster, to investigate whether nonA, like the period gene, might encode species-specific behavioral information. Mutations in nonA can disrupt both visual behavior and the courtship song in D. melanogaster. The lovesong of nonA(diss) mutant males superficially resembles that of D. virilis, a species that diverged from D. melanogaster 40-60 mya. Transformation of the cloned D. virilis nonA gene into D. melanogaster hosts carrying a synthetic deletion of the nonA locus restored normal visual function (the phenotype most sensitive to nonA mutation). However, the courtship song of transformant males showed several features characteristic of the corresponding D. virilis signal, indicating that nonA can act as a reservoir for species-specific information. This candidate gene approach, together with interspecific transformation, can therefore provide a direct avenue to explore potential speciation genes in genetically and molecularly tractable organisms such as Drosophila.

Animals↗
PubMed2026

Genome-wide SNP data support species boundaries in sympatric Polylepis Ruiz & Pav. (Rosaceae) species from Bolivia and Ecuador.

Species delimitation in the South American genus Polylepis is notoriously challenging due to high morphological similarity and phenotypic plasticity, likely driven by hybridization and gene flow. Previous phylogenetic studies suggested that genetic structure aligns more strongly with geography than with taxonomy, questioning existing species concepts and hampering conservation efforts. We used double-digest RAD sequencing (ddRADseq) to generate genome-wide SNP data for 11 Polylepis species sampled across multiple localities in Bolivia and Ecuador. Population genetic analyses, phylogenetic inference, and network approaches were combined to assess whether genetic structure aligns more closely with taxonomy or geography. Morphologically defined species formed largely cohesive genetic lineages across regions, with species identity explaining substantially more genetic variation than locality. While localized admixture and reticulation were detected among closely related taxa, widespread species showed strong genetic cohesion and clear separation from congeners. Our results indicate that the sampled Polylepis species from Bolivia and Ecuador maintain distinct genetic identities despite localized signals consistent with gene flow. This genome-wide support for current taxonomy highlights Polylepis as a valuable model for studying speciation under gene flow and indicates that multiple geographic sampling will be essential in reconstructing a robust phylogeny of the genus, with important implications for conservation planning in Andean montane forests.

Bolivia↗
PubMed1999

Four intracellular genomes direct weevil biology: nuclear, mitochondrial, principal endosymbiont, and Wolbachia.

Cell physiology in the weevil Sitophilus oryzae is coordinated by three integrated genomes: nuclear, mitochondrial, and the "S. oryzae principal endosymbiont" (SOPE). SOPE, a cytoplasmic bacterium (2 x 10(3) bacteria per specialized bacteriocyte cell and 3 x 10(6) bacteria per weevil) that belongs to the proteobacteria gamma3-subgroup, is present in all weevils studied. We discovered a fourth prokaryotic genome in somatic and germ tissues of 57% of weevil strains of three species, S. oryzae, Sitophilus zeamais, and Sitophilus granarius, distributed worldwide. We assigned this Gram-negative prokaryote to the Wolbachia group (alpha-proteobacteria), on the basis of 16S rDNA sequence and fluorescence in situ DNA-RNA hybridization (FISH). Both bacteria, SOPE and Wolbachia, were selectively eliminated by combined heat and antibiotic treatments. Study of bacteria involvement in this insect's genetics and physiology revealed that SOPE, which induces the specific differentiation of the bacteriocytes, increases mitochondrial oxidative phosphorylation through the supply of pantothenic acid and riboflavin. Elimination of this gamma3-proteobacterium impairs many physiological traits. By contrast, neither the presence nor the absence of Wolbachia significantly affects the weevil's physiology. Wolbachia, disseminated throughout the body cells, is in particularly high density in the germ cells, where it causes nucleocytoplasmic incompatibility. The coexistence of two distinct types of intracellular proteobacteria at different levels of symbiont integration in insects illustrates the genetic complexity of animal tissue. Furthermore, evolutionary timing can be inferred: first nucleocytoplasm, then mitochondria, then SOPE, and finally Wolbachia. Symbiogenesis, the genetic integration of long-term associated members of different species, in the weevil appears to be a mechanism of speciation (with Wolbachia) and provides a means for animals to acquire new genes that permit better adaptation to the environment (with SOPE).

Biological Evolution↗
PubMed2006

Contrasting patterns of introgression at X-linked loci across the hybrid zone between subspecies of the European rabbit (Oryctolagus cuniculus).

Hybrid zones provide an excellent opportunity for studying the consequences of genetic changes between closely related taxa. Here we investigate patterns of genetic variability and gene flow at four X-linked loci within and between the two subspecies of European rabbit (Oryctolagus cuniculus cuniculus and O. c. algirus). Two of these genes are located near the centromere and two are located near the telomeres. We observed a deep split in the genealogy of each gene with the root located along the deepest branch in each case, consistent with the evolution of these subspecies in allopatry. The two centromeric loci showed low levels of variability, high levels of linkage disequilibrium, and little introgression between subspecies. In contrast, the two telomeric loci showed high levels of variability, low levels of linkage disequilibrium, and considerable introgression between subspecies. These data are consistent with suppression of recombination near the centromere of the rabbit X chromosome. These observations support a view of speciation where genomic incompatibilities at different loci in the genome create localized differences in levels of gene flow between nascent species.

Animals↗
PubMed2004

Chromosomes and speciation in Mus musculus domesticus.

Thirty years after its identification, the model of chromosomal speciation in Mus musculus domesticus is reevaluated using the methods of population biology, molecular cytogenetics and functional genomics. Three main points are considered: (1) the structural predisposition of M. m. domesticus chromosomes to Robertsonian fusion; (2) the impediment of structural heterozygosity to gene flow between populations of mice with karyotypes rearranged by Robertsonian fusion and between them and populations with the standard all-acrocentric 40-chromosome karyotype; (3) the selective advantage of chromosomal novelty, essential for the attainment of homozygosis and the rapid fixation of the new karyotype in the population.

Animals↗
PubMed1992

Evolution of the retrotransposons TRS/ingi and of the tubulin genes in trypanosomes.

The African trypanosomes have genomes of high plasticity, as demonstrated for instance by their ability to shuffle their genes around, coding for variant-specific surface glycoproteins (VSGs). Another indication of their genome plasticity is the presence of multiple retro-elements. The retrotransposon-like element TRS/ingi is present in many copies in the genome of trypanosomes. One particular derivative of TRS/ingi, called TUBIS, had previously been found to interrupt a tubulin gene in a particular strain of T. brucei. Here both TRS/ingi and TUBIS were studied by hybridizing genomic DNA of various strains and species of trypanosomes with suitable probes in order to elucidate the evolution of this family of retro-elements. The TSR/ingi elements are highly repeated and have very long open reading frames, while TUBIS clearly is a truncated, inactivated form of this element, found in only one particular chromosomal location. Both elements were shown to be present in several strains and species of the subgenus Trypanozoon, in particular in T. brucei brucei, T. gambiense, T. rhodesiense, T. equiperdum and T. evansi. They could not be detected in species of other subgenera, in particular in T. congolense and T. cruzi. These findings suggest that the retrotransposon TRS/ingi was acquired by trypanosomes only after divergence of present day subgenera. The TUBIS element was found in exactly the same chromosomal location (at the 3' end of the tubulin gene cluster) in many different strains and species of the subgenus Trypanozoon. This shows that the element was transposed to this location before speciation of the subgenus. Although, TRS/ingi is unlikely to be involved directly in VSG switching, it may have contributed to the genome plasticity of trypanosomes.

Animals↗
PubMed1989

Haptoglobin DNA polymorphism in subterranean mole rats of the Spalax ehrenbergi superspecies in Israel.

We analyzed the genetic diversity and environmental correlates of the haptoglobin (Hp) gene by RFLP analysis of 121 subterranean mole rats, comprising 13 populations belonging to the 4 chromosomal species (2n = 52, 54, 58 and 60) of the actively speciating Spalax ehrenbergi superspecies in Israel. The following results were indicated: (i) Out of the six restriction enzymes we tested, we found polymorphism only in TaqI, with three allelic fragments, and described their geographic patterning. (ii) Genetic diversity of Hp was highest in the centre of the range. (iii) The two major alleles showed high significant and opposite correlation with humidity. (iv) Genetic differentiation analysis indicated that 40 per cent of the Hp variation was within, and 60 per cent between populations. We conclude that climatic selection plays an important role in haptoglobin genetic differentiation.

Animals↗
PubMed1991

Polymorphism of C4 and CYP21 genes in various primate species.

To study the genetic heterogeneity of the C4 and CYP21 genes in selected primate species we used the technique of restriction fragment length polymorphism (RFLP). Genomic DNA was digested using several restriction endonucleases and filters were hybridized with a 500 bp BamHI/KpnI fragment derived from the 5' section of a human C4-cDNA and with a 1700 bp BamHI obtained from a human CYP21 gene. Abundant RFLP heterogeneity was observed for the C4 genes within a rhesus monkey population but not for the chimpanzee colony analyzed. Duplicated C4-CYP21 clusters can be traced back in humans, but also in chimpanzees, orang-utans and rhesus monkeys. Thus, duplication of the basic C4-CYP21 cluster in primates may have happened more than 30 million years ago. Non-duplicated C4-CYP21 regions were found for the gorilla and orang-utan. Apart from this, shortened C4A and C4B genes were observed in chimpanzees, orang-utans and rhesus monkeys, whereas the so-called long variety of the C4A gene appears to be present in humans and orang-utans. This ancestral modification, resulting from an insertion of a 6.5 kb intron in the C4A gene, therefore predates at least speciation of human and orang-utan which is estimated to have taken place more than 12 million years ago.

Animals↗