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Results for “genomic divergence”

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At least 19 recordsLinked to original sources

PubMed2025

Doubled Genomes, Divergent Fates: Genomic Insights Into Diversification in an Allotetraploid Cavefish.

Cave environments impose unique challenges that drive remarkable genetic and phenotypic changes in cave-dwelling organisms. In this study, we investigated the genomic basis of adaptation in the small eye golden-line fish (Sinocyclocheilus microphthalmus), an allotetraploid cavefish endemic to Guangxi, China. Using whole-genome resequencing data from 47 individuals across six cave locations, we examined how neutral and selective forces influence diversification. Our analyses uncovered significant population structure indicative of allopatric divergence, along with evidence of locus-specific selection contributing to genomic differentiation. We identified seven single outlier clusters (SOCs), each tied to the divergence of specific populations, underscoring the role of local processes in driving diversity. Genes associated with vision showed relaxed selection, likely reflecting adaptation to darkness, while positive selection on other loci revealed additional functional shifts. Notably, allopolyploidy was found to fuel divergence through subgenome-specific patterns and asymmetric evolution within SOCs and among homoeologs. Taken together, these findings provide valuable insights into mechanisms of cave evolution and illustrate how allotetraploid genomes can facilitate diversification, potentially contributing to speciation in extreme environments.

Animals↗

PubMed2006

Genomic divergences among cattle, dog and human estimated from large-scale alignments of genomic sequences.

BACKGROUND: Approximately 11 Mb of finished high quality genomic sequences were sampled from cattle, dog and human to estimate genomic divergences and their regional variation among these lineages. RESULTS: Optimal three-way multi-species global sequence alignments for 84 cattle clones or loci (each >50 kb of genomic sequence) were constructed using the human and dog genome assemblies as references. Genomic divergences and substitution rates were examined for each clone and for various sequence classes under different functional constraints. Analysis of these alignments revealed that the overall genomic divergences are relatively constant (0.32-0.37 change/site) for pairwise comparisons among cattle, dog and human; however substitution rates vary across genomic regions and among different sequence classes. A neutral mutation rate (2.0-2.2 x 10(-9) change/site/year) was derived from ancestral repetitive sequences, whereas the substitution rate in coding sequences (1.1 x 10(-9) change/site/year) was approximately half of the overall rate (1.9-2.0 x 10(-9) change/site/year). Relative rate tests also indicated that cattle have a significantly faster rate of substitution as compared to dog and that this difference is about 6%. CONCLUSION: This analysis provides a large-scale and unbiased assessment of genomic divergences and regional variation of substitution rates among cattle, dog and human. It is expected that these data will serve as a baseline for future mammalian molecular evolution studies.

Animals↗

PubMed2002

A mathematical method for determining genome divergence and species delineation using AFLP.

The delineation of bacterial species is presently achieved using direct DNA-DNA relatedness studies of whole genomes. It would be helpful to obtain the same genomically based delineation by indirect methods, provided that descriptions of individual genome composition of bacterial genomes are obtained and included in species descriptions. The amplified fragment length polymorphism (AFLP) technique could provide the necessary data if the nucleotides involved in restriction and amplification are fundamental to the description of genomic divergences. Firstly, in order to verify that AFLP analysis permits a realistic exploration of bacterial genome composition, the strong correspondence between predicted and experimental AFLP data was demonstrated using Agrobacterium strain C58 as a model system. Secondly, a method is proposed for determining current genome mispairing and evolutionary genome divergences between pairs of bacteria, based on arbitrary sampling of genomes by using AFLP. The measure of current genome mispairing was validated by comparison with DNA-DNA relatedness data, which itself correlates with base mispairing. The evolutionary genome divergence is the estimated rate of nucleotide substitution that has occurred since the strains diverged from a common ancestor. Current genome mispairing and evolutionary genome divergence were used to compare members of Agrobacterium, used as a model of closely related genomic species. A strong and highly significant correlation was found between calculated genome mispairing and DNA-DNA relatedness values within genomic species. The canonical 70% DNA-DNA hybridization value used to delineate genomic species was found to correspond to a range of current genome mispairing of 13-13.6%. These limits correspond to 0.097 and 0.104 nucleotide substitutions per site, respectively. In addition, experimental data showed that the large Ti and cryptic plasmids of Agrobacterium had little effect on the estimation of genome divergence. Evolutionary genome divergence was used for phylogenetic inferences. Data showed that members of the same genomic species clustered consistently, as supported by bootstrap resampling. On the basis of these results, it is proposed that the genomic delineation of bacterial species could be based, in future, on phylogenetic groups supported by bootstraps and genome descriptions of individual strains, obtained by AFLP analysis, recorded in accessible databases; this approach might eventually replace DNA-DNA hybridization studies.

Biological Evolution↗

PubMed2004

Stabilizing selection on genomic divergence in a wild fish population.

Conservation programs use breeding protocols to increase genomic divergence (by mating genetically dissimilar individuals) in an attempt to circumvent population declines resulting from inbreeding depression. However, disruption of either beneficial gene complexes or local genetic adaptations can lead to outbreeding depression, and thus, there should be a reduction in fitness of individuals at either end of the genomic divergence continuum. Although such simultaneous inbreeding and outbreeding depression has been observed in plant populations, it rarely has been demonstrated in animal populations. Here, I use both genetic and phenotypic measures to show that there is stabilizing selection on genomic divergence in a wild population of bluegill sunfish (Lepomis macrochirus). I also show that breeding individuals that exercise mate choice produce offspring that are closer to the optimal level of genomic divergence than random mating alone would predict.

Animals↗

PubMedDate not supplied

Genomic divergence between human and chimpanzee estimated from large-scale alignments of genomic sequences.

To study the genomic divergence between human and chimpanzee, large-scale genomic sequence alignments were performed. The genomic sequences of human and chimpanzee were first masked with the RepeatMasker and the repeats were excluded before alignments. The repeats were then reinserted into the alignments of nonrepetitive segments and entire sequences were aligned again. A total of 2.3 million base pairs (Mb) of genomic sequences, including repeats, were aligned and the average nucleotide divergence was estimated to be 1.22%. The Jukes-Cantor (JC) distances (nucleotide divergences) in nonrepetitive (1.44 Mb) and repetitive sequences (0.86 Mb) are 1.14% and 1.34%, respectively, suggesting a slightly higher average rate in repetitive sequences. Annotated coding and noncoding regions of homologous chimpanzee genes were also retrieved from GenBank and compared. The average synonymous and nonsynonymous divergences in 88 coding genes are 1.48% and 0.55%, respectively. The JC distances in intron, 5' flanking, 3' flanking, promoter, and pseudogene regions are 1.47%, 1.41%, 1.68%, 0.75%, and 1.39%, respectively. It is not clear why the genetic distances in most of these regions are somewhat higher than those in genomic sequences. One possible explanation is that some of the genes may be located in regions with higher mutation rates.

Animals↗

PubMed2025

Patterns of Genomic Divergence and Introgression in Two Primulina Hybrid Zones.

Hybrid zones have long been promoted as natural laboratories for understanding the mechanisms of speciation. Multiple or replicated hybrid zones are particularly informative, as they allow for assessing the consistency of genomic divergence and introgression across different environmental contexts and demographic histories, thereby improving our understanding of the factors that drive or hinder speciation on a broader scale. Here, using whole-genome resequencing data, we compare the patterns of genomic divergence and introgression in two Primulina hybrid zones. We found that genomic divergence in both hybrid zones is largely shaped by neutral processes, with only a few genomic regions showing signatures of balancing or lineage-specific selection. Genomic cline analyses identified numerous SNPs that showed significantly steeper clines and biased centres than the genome-wide expectation in both hybrid zones, consistent with the existence of reproductive barriers. Within regions of restricted gene flow, we identified 21 genes shared between the two hybrid zones. Annotation of gene function revealed that several genes are involved in reproductive processes. In addition, many zone-specific outlier loci were linked to genes associated with pollen and flower development, suggesting that these barriers may contribute to reproductive isolation under localised ecological conditions. Overall, these findings suggest that while certain reproductive barriers remain consistent across independent hybrid zones, others may be contingent on local environmental contexts. Our results demonstrate that both general and zone-specific mechanisms contribute to reproductive isolation in Primulina, providing empirical evidence that some genomic barriers recur across independent hybrid zones while others arise through localised adaptation.

Lamiales↗

PubMed2004

Mammalian microevolution in action: adaptive edaphic genomic divergence in blind subterranean mole-rats.

Genomic diversity of anonymous regions across the genome, most probably including coding and noncoding amplified fragment length polymorphisms (AFLPs), was examined in 20 individuals of the blind mole-rat, Spalax galili, one of four allospecies of the Spalax ehrenbergi superspecies of blind subterranean mole-rats in Israel. We compared 10 individuals from two nearby populations in Upper Galilee, separated by only a few dozen to hundreds of metres and living in two sharply contrasting ecologies: white chalk and rendzina soil with Sarcopterium spinosum and Majorana syriaca versus black volcanic basalt soil with Carlina hispanica-Psorelea bitominosa and Alhagi graecorum plant formations. The microsite tested ranged in an area of less than 10000 m2. Out of 729 AFLP loci, 433 (59.4%) were polymorphic, with 211 soil unique alleles. Genetic polymorphism was significantly higher on the ecologically more xeric and stressful chalky rendzina soil than on the neighbouring mesic basalt soil. This is a remarkable pattern for a mammal that can disperse each generation between tens to hundreds of metres. These results cannot be explained by migration (which causes homogenization) or by chance (which will exclude sharp genomic soil divergence). Natural selection is the only evolutionary adaptive force that can cause genetic divergence across the genome matching the sharp microscale ecological contrast.

Animals↗

PubMed2003

Rapid genome divergence at orthologous low molecular weight glutenin loci of the A and Am genomes of wheat.

To study genome evolution in wheat, we have sequenced and compared two large physical contigs of 285 and 142 kb covering orthologous low molecular weight (LMW) glutenin loci on chromosome 1AS of a diploid wheat species (Triticum monococcum subsp monococcum) and a tetraploid wheat species (Triticum turgidum subsp durum). Sequence conservation between the two species was restricted to small regions containing the orthologous LMW glutenin genes, whereas >90% of the compared sequences were not conserved. Dramatic sequence rearrangements occurred in the regions rich in repetitive elements. Dating of long terminal repeat retrotransposon insertions revealed different insertion events occurring during the last 5.5 million years in both species. These insertions are partially responsible for the lack of homology between the intergenic regions. In addition, the gene space was conserved only partially, because different predicted genes were identified on both contigs. Duplications and deletions of large fragments that might be attributable to illegitimate recombination also have contributed to the differentiation of this region in both species. The striking differences in the intergenic landscape between the A and A(m) genomes that diverged 1 to 3 million years ago provide evidence for a dynamic and rapid genome evolution in wheat species.

Base Sequence↗

PubMed2001

Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees.

To study the genomic divergences among hominoids and to estimate the effective population size of the common ancestor of humans and chimpanzees, we selected 53 autosomal intergenic nonrepetitive DNA segments from the human genome and sequenced them in a human, a chimpanzee, a gorilla, and an orangutan. The average sequence divergence was only 1.24% +/- 0.07% for the human-chimpanzee pair, 1.62% +/- 0.08% for the human-gorilla pair, and 1.63% +/- 0.08% for the chimpanzee-gorilla pair. These estimates, which were confirmed by additional data from GenBank, are substantially lower than previous ones, which included repetitive sequences and might have been based on less-accurate sequence data. The average sequence divergences between orangutans and humans, chimpanzees, and gorillas were 3.08% +/- 0.11%, 3.12% +/- 0.11%, and 3.09% +/- 0.11%, respectively, which also are substantially lower than previous estimates. The sequence divergences in other regions between hominoids were estimated from extensive data in GenBank and the literature, and Alus showed the highest divergence, followed in order by Y-linked noncoding regions, pseudogenes, autosomal intergenic regions, X-linked noncoding regions, synonymous sites, introns, and nonsynonymous sites. The neighbor-joining tree derived from the concatenated sequence of the 53 segments--24,234 bp in length--supports the Homo-Pan clade with a 100% bootstrap value. However, when each segment is analyzed separately, 22 of the 53 segments (approximately 42%) give a tree that is incongruent with the species tree, suggesting a large effective population size (N(e)) of the common ancestor of Homo and Pan. Indeed, a parsimony analysis of the 53 segments and 37 protein-coding genes leads to an estimate of N(e) = 52,000 to 96,000. As this estimate is 5 to 9 times larger than the long-term effective population size of humans (approximately 10,000) estimated from various genetic polymorphism data, the human lineage apparently had experienced a large reduction in effective population size after its separation from the chimpanzee lineage. Our analysis assumes a molecular clock, which is in fact supported by the sequence data used. Taking the orangutan speciation date as 12 to 16 million years ago, we obtain an estimate of 4.6 to 6.2 million years for the Homo-Pan divergence and an estimate of 6.2 to 8.4 million years for the gorilla speciation date, suggesting that the gorilla lineage branched off 1.6 to 2.2 million years earlier than did the human-chimpanzee divergence.

Alu Elements↗

PubMed2005

Transmission ratio distortion in intraspecific hybrids of Mimulus guttatus: implications for genomic divergence.

We constructed a genetic linkage map between two divergent populations of Mimulus guttatus. We genotyped an F(2) mapping population (N = 539) at 154 AFLP, microsatellite, and gene-based markers. A framework map was constructed consisting of 112 marker loci on 14 linkage groups with a total map length of 1518 cM Kosambi. Nearly half of all markers (48%) exhibited significant transmission ratio distortion (alpha = 0.05). By using a Bayesian multipoint mapping method and visual inspection of significantly distorted markers, we detected 12 transmission ratio distorting loci (TRDL) throughout the genome. The high degree of segregation distortion detected in this intraspecific map indicates substantial genomic divergence that perhaps suggests genomic incompatibilities between these two populations. We compare the pattern of transmission ratio distortion in this map to an interspecific map constructed between M. guttatus and M. nasutus. A similar level of segregation distortion is detected in both maps. Collinear regions between maps are compared to determine if there are shared genetic patterns of non-Mendelian segregation distortion within and among Mimulus species.

Chromosome Mapping↗

PubMed1994

[Chinese strain of hepatitis D virus: molecular cloning and sequencing, and the significance of its genome divergence].

The hepatitis D virus (HDV) obtained from a chronic asymptomatic HDV/HBsAg carrier (SZ 93) in Sichuan province was cloned with 1,684 nucleotides in full-length genome by reverse transcription-PCR. Comparison of SZ 93 with those obtained from different geographic area: i.e., Italia, United States, British, Nauru, Taiwan, Netherland, showed 81.8%-95.4% homology in nucleotide sequence of whole genome, 88.9%-96.1% homology in nucleotide sequence of HDAg-coding region, and 86.4%-93.0% homology in amino acid sequence of HDAg protein. Also, another isolate (SZ 92) obtained from a chronic severe hepatitis patient in Sichuan was cloned with HDAg-coding region. There were some mutations in SZ 92 compared with SZ 93 as well as the other clones mentioned above. The meaning for the genome divergence of HDV SZ 93 and SZ 92 was discussed.

Adult↗

PubMed1985

Introgression between two cutthroat trout subspecies with substantial karyotypic, nuclear and mitochondrial genomic divergence.

The authors used allozymes encoded by nuclear genes and restriction enzyme analysis of mitochondrial DNA (mtDNA) to study secondary contact between westslope (Salmo clarki lewisi) and Yellowstone cutthroat trout (Salmo clarki bouvieri) in Forest Lake, Montana. Eleven diagnostic allozyme loci identified this as a random-mating hybrid swarm. No parental, first-generation hybrid or backcross genotypes were detected in the sample (N = 33), and genotype distributions at all the variable loci conform to binomial expectations. There is little linkage disequilibrium between the diagnostic loci, indicating that the nuclear genomes of the two subspecies are largely randomly associated. The allozymes and mtDNA give identical estimates of the proportional genetic contribution of each subspecies. Thus, males and females from both subspecies have contributed equally to this hybrid swarm. Although these subspecies have accumulated substantial genetic divergence between their nuclear (Nei's D = 0.34) and mitochondrial (2% sequence divergence) genomes, this has not resulted in a genetic barrier to exchange between them.

Alleles↗

PubMed2006

Quantification of insect genome divergence.

The recent sequencing of twelve insect genomes has enabled us to quantify their divergence using synteny conservation and sequence identity of single-copy orthologs. Protein identity correlates well with synteny and is about three times more conserved, an observation consistent with comparisons among vertebrates. The observed distribution of the lengths of synteny blocks follows a power law and differs from the expectations of the currently accepted random breakage model. Our results show that there is only limited selection for conservation of gene order and reveal a few hundred genes, proximity among which seems to be vital.

Animals↗

PubMed2003

Comparative sequencing of human and chimpanzee MHC class I regions unveils insertions/deletions as the major path to genomic divergence.

Despite their high degree of genomic similarity, reminiscent of their relatively recent separation from each other ( approximately 6 million years ago), the molecular basis of traits unique to humans vs. their closest relative, the chimpanzee, is largely unknown. This report describes a large-scale single-contig comparison between human and chimpanzee genomes via the sequence analysis of almost one-half of the immunologically critical MHC. This 1,750,601-bp stretch of DNA, which encompasses the entire class I along with the telomeric part of the MHC class III regions, corresponds to an orthologous 1,870,955 bp of the human HLA region. Sequence analysis confirms the existence of a high degree of sequence similarity between the two species. However, and importantly, this 98.6% sequence identity drops to only 86.7% taking into account the multiple insertions/deletions (indels) dispersed throughout the region. This is functionally exemplified by a large deletion of 95 kb between the virtual locations of human MICA and MICB genes, which results in a single hybrid chimpanzee MIC gene, in a segment of the MHC genetically linked to species-specific handling of several viral infections (HIV/SIV, hepatitis B and C) as well as susceptibility to various autoimmune diseases. Finally, if generalized, these data suggest that evolution may have used the mechanistically more drastic indels instead of the more subtle single-nucleotide substitutions for shaping the recently emerged primate species.

Animals↗

PubMed2025

Genomic Divergence Shaped the Genetic Regulation of Meiotic Homologous Recombination in Brassica Allopolyploids.

The tight regulation of meiotic recombination between homologs is disrupted in Brassica AAC allotriploids, a genomic configuration that may have facilitated the formation of rapeseed (Brassica napus L.) ∼7,500 years ago. Indeed, the presence of the haploid C genome induces supernumerary crossovers between homologous A chromosomes with dramatically reshaped distribution. However, the genetic mechanisms driving this phenomenon and their divergence between nascent and established lineages remain unclear. To address these concerns, we generated hybrids carrying additional C chromosomes derived either from an established lineage of the allotetraploid B. napus or from its diploid progenitor B. oleracea. We then assessed recombination variation across twelve populations by mapping male meiotic crossovers using single nucleotide polymorphism markers evenly distributed across the sequenced A genome. Our findings reveal that the C09 chromosome of B. oleracea is responsible for the formation of additional crossovers near pericentromeric regions. Interestingly, its counterpart from an established lineage of B. napus shows no significant effect on its own, despite having a similar content of meiotic genes. However, we showed that the B. napus C09 chromosome influences crossover formation through inter-chromosomal epistatic interactions with other specific C chromosomes. These results provide new insights into the genetic regulation of homologous recombination in Brassica and emphasize the role of genomic divergence since the formation of the allopolyploid B. napus.

Meiosis↗

PubMed2005

Genomic divergence of Escherichia coli strains: evidence for horizontal transfer and variation in mutation rates.

This report describes the sequencing in the Escherichia coli B genome of 36 randomly chosen regions that are present in most or all of the fully sequenced E. coli genomes. The phylogenetic relationships among E. coli strains were examined, and evidence for the horizontal gene transfer and variation in mutation rates was determined. The overall phylogenetic tree indicated that E. coli B and K-12 are the most closely related strains, with E. coli O157:H7 being more distantly related, Shigella flexneri 2a even more, and E. coli CFT073 the most distant strain. Within the B, K-12, and O157:H7 clusters, several regions supported alternative topologies. While horizontal transfer may explain these phylogenetic incongruities, faster evolution at synonymous sites along the O157:H7 lineage was also identified. Further interpretation of these results is confounded by an association among genes showing more rapid evolution and results supporting horizontal transfer. Using genes supporting the B and K-12 clusters, an estimate of the genomic mutation rate from a long-term experiment with E. coli B, and an estimate of 200 generations per year, it was estimated that B and K-12 diverged several hundred thousand years ago, while O157:H7 split off from their common ancestor about 1.5-2 million years ago.

Codon↗

PubMed2004

Differential loss of ancestral gene families as a source of genomic divergence in animals.

A phylogenetic approach was used to reconstruct the pattern of an apparent loss of 2106 ancestral gene families in four animal genomes (Caenorhabditis elegans, Drosophila melanogaster, human and fugu). Substantially higher rates of loss of ancestral gene families were found in the invertebrates than in the vertebrates. These results indicate that the differential loss of ancestral gene families can be a significant factor in the evolutionary diversification of organisms.

Animals↗

PubMed2001

Ancestral divergence, genome diversification, and phylogeographic variation in subpopulations of sorbitol-negative, beta-glucuronidase-negative enterohemorrhagic Escherichia coli O157.

The O157:H7 lineage of enterohemorrhagic Escherichia coli is a geographically disseminated complex of highly related genotypes that share common ancestry. The common clone that is found worldwide carries several markers of events in its evolution, including markers for acquisition of virulence genes and loss of physiological characteristics, such as sorbitol fermentation ability and beta-glucuronidase production. Populations of variants that are distinct with respect to motility and the sorbitol and beta-glucuronidase markers appear to have diverged at several points along the inferred evolutionary pathway. In addition to these variants, distinct subpopulations of the contemporary non-sorbitol-fermenting, beta-glucuronidase-negative O157:H7 clone were recently detected among bovine and human clinical isolates in the United States by using high-resolution genome comparison. In order to determine if these recently described subpopulations were derived from a regional or ancestral divergence event, we used octamer-based genome scanning, marker sorting, and DNA sequence analysis to examine their phylogenetic relationship to populations of non-sorbitol-fermenting, beta-glucuronidase negative O157:H7 and O157:H- strains from Australia. The inferred phylogeny is consistent with the hypothesis that subpopulations on each continent resulted from geographic spread of an ancestral divergence event and subsequent expansion of distinct subpopulations. Marker sorting and DNA sequence analyses identified sets of monophyletic markers consistent with the pattern of divergence and demonstrated that phylogeographic variation occurred through emergence of regional subclones and concentration of regional polymorphisms among distinct subpopulations. DNA sequence analysis of representative polyphyletic markers showed that genome diversity accrued through random drift and bacteriophage-mediated events.

Animals↗