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Results for “Genetic Introgression”

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PubMed2000

Genetic obesity unmasks nonlinear interactions between murine type 2 diabetes susceptibility loci.

Nonlinear interactions between obesity and genetic risk factors are thought to determine susceptibility to type 2 diabetes. We used genetic obesity as a tool to uncover latent differences in diabetes susceptibility between two mouse strains, C57BL/6J (B6) and BTBR. Although both BTBR and B6 lean mice are euglycemic and glucose tolerant, lean BTBR x B6 F1 male mice are profoundly insulin resistant. We hypothesized that the genetic determinants of the insulin resistance syndrome might also predispose genetically obese mice to severe diabetes. Introgressing the ob allele into BTBR revealed large differences in diabetes susceptibility between the strain backgrounds. In a population of F2-ob/ob mice segregating for BTBR and B6 alleles, we observed large variation in pancreatic compensation for the underlying insulin resistance. We also detected two loci that substantially modify diabetes severity, and a third locus that strongly links to fasting plasma insulin levels. Amplification of the genetic signal from these latent diabetes susceptibility alleles in F2-ob/ob mice permitted discovery of an interaction between the two loci that substantially increased the risk of severe type 2 diabetes.

Alleles↗

PubMed2002

A new locus for resistance to gamma-radiation-induced thymic lymphoma identified using inter-specific consomic and inter-specific recombinant congenic strains of mice.

Mice of the C57BL/6J inbred strain develop thymic lymphomas at very high frequency after acute gamma-irradiation, while mice of several inbred strains derived from the wild progenitor of the Mus spretus species and their F1 hybrids with C57BL/6J appear extremely resistant. Analysis of the genetic determinism of the gamma-radiation-induced thymic lymphoma (RITL) resistance with the help of inter-specific consomic strains (ICS), which carry a single introgressed Mus spretus chromosome on a C57BL/6J genetic background, provide significant evidence for the existence of a thymic lymphoma resistance (Tlyr1) locus on chromosome 19. The subsequent analysis of the backcross progeny resulting from a cross between consomic mice heterozygous for the Mus spretus chromosome 19 and C57BL/6J mice, together with the study of inter-specific recombinant congenic strains (IRCS), suggest that this Tlyr1 locus maps within the D19Mit60-D19Mit40 chromosome interval. In addition to the discovery of a new locus controlling RITL development, our study emphasizes the value of ICS and IRCS for the genetic analysis of cancer predisposition.

Animals↗

PubMed1998

The impact of genetic markers on selection.

Genetic marker technologies, such as marker-assisted selection, parentage identification, and gene introgression can be applied to livestock selection programs. Highly saturated genetic maps are now available for cattle, swine, and sheep to provide the genetic framework for developing MAS programs. These programs rely on three phases for commercialization of the technology: the detection phase, in which quantitative trait loci are located and their effects on the phenotype measured; the evaluation phase, in which the markers are evaluated in commercial populations; and the implementation phase, in which markers are combined with phenotypic and pedigree information in genetic evaluation for predicting the genetic merit of individuals within the population. Predicting the economic impact of genetic technologies is a complex process that requires quantitative prediction and economic analysis. Evaluating the impact of these benefits across an industry can be achieved through a process in which gains from implementation of a genetic technology are assessed at the individual, enterprise, and industry levels. A pattern of annual benefits and costs can be predicted using gene flows that can be evaluated by conventional economic analysis.

Animals↗

PubMed2000

Mitochondrial haplotype diversity among Portuguese brown trout Salmo trutta L. populations: relevance to the post-pleistocene recolonization of northern Europe.

Mitochondrial haplotype diversity in seven Portuguese populations of brown trout, Salmo trutta L., was investigated by sequencing the 5' end of the mitochondrial DNA (mtDNA) control region. Five new haplotypes were described for this species, each two to three mutational steps distant from the common north Atlantic haplotype. Significant population subdivision of mtDNA haplotypes was also apparent. Based on these results, as well as on published data describing the distribution of both mtDNA haplotypes and allozyme alleles throughout Europe, the postglacial recolonization of northern Europe was re-evaluated. It is argued that the available data do not support the contribution of two major glacial refugia (southwest Atlantic and Ponto-Caspian Basin) to this postglacial recolonization, as proposed in a recently published model. The unique genetic architecture of Portuguese brown trout within the Atlantic-basin clade of this species represents a highly valuable genetic resource that should be protected from introgression with nonendemic strains of hatchery fish.

Animals↗

PubMed1992

Origin of Gila seminuda (Teleostei: Cyprinidae) through introgressive hybridization: implications for evolution and conservation.

Morphological and genetic characters from cyprinid fishes of the genus Gila were examined to assess a hypothesized hybrid origin of Gila seminuda from the Virgin River, Arizona-Nevada-Utah. The presumed parents, Gila robusta robusta and Gila elegans, are clearly differentiated from one another based on morphology, allozymes, and mtDNA haplotypes. G. seminuda is morphologically intermediate and polymorphic at allozyme loci diagnostic for the parental species. Restriction endonuclease analysis of mtDNA showed G. seminuda nearly identical to G. elegans. These results support an origin of the bisexual taxon G. seminuda through introgressive hybridization. The Gila population in the Moapa River, Nevada, also appears to be of hybrid origin and is considered a distinctive population of G. seminuda. Inter-specific hybridization is potentially an important mode of evolution among western North American fishes, and valid species of hybrid origin may exist in other groups as well. Consideration of this mode of evolution argues for the need to conserve entire species complexes.

Animals↗

PubMed2025

Molecular signatures of adaptive introgression and selection in contact zones of closely related pine species (Pinus genus).

BACKGROUND: Natural hybridization plays a key role in shaping genetic diversity, local adaptation, and the dynamics of speciation through interspecific gene flow. Hybrid zones serve as valuable natural systems for studying these processes. In this research, we used genotypic data at thousands of nuclear SNPs to investigate genomic outcomes of hybridization and selection across three contact zones of closely related pine species including Scots pine (Pinus sylvestris L.) and dwarf mountain pine (P. mugo T.). Reference allopatric stands of parental species were used to assess introgression dynamics. RESULTS: Individuals from the hybrid zones showed distinct genetic ancestry patterns and were assigned to groups including putative pure species, first-generation hybrids, and advanced backcrosses. Genotypes of the majority of hybrids were shifted towards P. mugo ancestry. Most outlier loci were shared across all sympatric populations, although some were specific to individual contact zones. The identified outliers were mainly associated with regulatory biological processes related to phosphorylation, proteolysis, and transmembrane transport. Signatures of local adaptation varied in different genetic classes in contact zones and they were strongest in pure P. sylvestris and hybrids with a majority of P. sylvestris ancestry. The pattern suggests that it may be driven by adaptation to peat bog habitats situated outside the species’ core ecological niche. CONCLUSIONS: Our findings indicate strong selective pressure acting on multiple genes in groups of hybrids and pure Pinus sylvestris individuals across all studied hybrid zones. In contrast, the weaker signal of selection observed in individuals with P. mugo ancestry suggests that relict populations of this species, which historically spread across postglacial peat bogs, were pre-adapted to such environments. While several outlier loci were shared across different contact zones, others were unique for one of them, indicating that local environmental pressures and adaptive introgression shape the genomic composition of the populations. These results highlight the role of hybridization in generating adaptive diversity and emphasize the evolutionary significance of hybrid zones in pines.

Hybridization, Genetic↗

PubMed1996

A genome-wide survey of hybrid incompatibility factors by the introgression of marked segments of Drosophila mauritiana chromosomes into Drosophila simulans.

In hybrids between Drosophila simulans and D. mauritiana, males are sterile and females are fertile, in compliance with HALDANE's rule. The genetic basis of this phenomenon was investigated by introgression of segments of the mauritiana genome into a simulans background. A total of 87 positions throughout the mauritiana genome were marked with P-element insertions and replicate introgressions were made by repeated backcrossing to simulans for 15 generations. The fraction of hemizgyous X chromosomal introgressions that are male sterile is approximately 50% greater than the fraction of homozygous autosomal segments. This result suggests that male sterility factors have evolved at a higher rate on the X, but chromosomal differences in segment length cannot be ruled out. The fraction of homozygous autosomal introgression that are male sterile is several times greater than the fraction that are either female sterile or inviable. This observation strongly indicates that male sterility factors have evolved more rapidly than either female sterility or inviability factors. These results, combined with previous work on these and other species, suggest that HALDANE's rule has at least two causes: recessivity of incompatibility factors and differential accumulation of sterility factors affecting males and females.

Animals↗

PubMed1977

Characterization of glycerol nonutilizing and protoperithecial mutants of Neurospora.

Mutants defective in polyol metabolism and/or in protoperithecial development were selected in Neurospora tetrasperma, a species in which protoperithecial development occurs at nonpermissively high temperature if certain polyols are used in lieu of sucrose as carbon source. Mutants selected for nonutilization of one of the four polyols tested, glycerol, mannitol, sorbitol, or xylitol, were usually found to be nonutilizers of the other three polyols as well. Mutants blocked at various stages of protoperithecial development complemented pairwise to produce more advanced developmental stages, usually mature protoperithecia and, when of opposite mating type, mature perithecia. About one-third of the mutants manifested both polyol auxotrophy and defective protoperithecial development upon initial isolation, but protoperithecial defectiveness in such mutants usually showed erratic segregation in crosses and/or instability to repeated vegetative transfer, whereas polyol auxotrophy usually did not and was, therefore, studied further. Two glycerol nonutilizing strains were introgressed into N. crassa to facilitate genetic analysis. One, glp-4, lacked both inducible and constitutive glycerol kinase and mapped to linkage group VI, between ad-1 and rib-1; the other, glp-5, lacked glyceraldehyde kinase and mapped to linkage group I, proximal to ad-9. Another mutant, gly-u(234), has been reported by other investigators to lack inducible glycerol kinase but to map to linkage group I, distal to ad-9.

Chromosome Mapping↗

PubMed2002

Speciation via introgressive hybridization in East African cichlids?

Speciation caused by introgressive hybridization occurs frequently in plants but its importance remains controversial in animal evolution. Here we report a case of introgressive hybridization between two ancient and genetically distinct species of Lake Tanganyika cichlids that led to the formation of a new species. Neolamprologus marunguensis contains mtDNA haplotypes from both parental species varying on average by 12.4% in the first section of the control region and by 5.2% in a segment of the cytochrome b gene. All individuals have almost identical DNA sequences in the flanking regions of the single-copy nuclear DNA locus TmoM27, and show a mosaic of alleles derived from both parental lineages in six microsatellite loci. Hence, our finding displays another mode of speciation in cichlid fishes. The increase of genetic and phenotypic diversity due to hybridization may contribute to the uniquely rapid pace of speciation in cichlids.

Animals↗

PubMed2002

Importance of hybridization between indigenous and nonindigenous freshwater species: an overlooked threat to North American biodiversity.

Biodiversity of North American freshwaters is among the greatest in the world. However, due to extensive habitat degradation, pollution, and introductions of nonindigenous species, this biodiversity is also among the most endangered. Unlike habitat degradation and pollution, nonindigenous species represent a permanent loss of biodiversity because their removal or control is often impossible. Most species introduced into nonnative North American ranges, however, are not from Eurasia but have been introduced from geographically isolated regions within North America. Although the ecological effects of introduced species have been widely documented, the effects of hybridization, especially between closely related species, represents an equally serious mechanism of extinction but is much less studied. Identification of which species are likely to hybridize after contact is of critical importance to prevent the further loss of native species. Molecular phylogenetics serves as a powerful tool to identify freshwater species at risk of introgression, if we can assume that genetic distance is a good predictor of the potential for hybridization. Although not a thorough review of all cases of hybridization, this article documents the extent and effects of hybridization in fishes, crayfishes, mussels, and other invertebrates in light of the currently accepted phylogenetic relationships. We suggest this approach may be the first step in addressing the potential threat of hybridization between many of the closely related species in North American fresh waters.

Animals↗

PubMed2025

Dissecting seed composition QTL from wild soybean: fine-mapping, candidate gene identification, and evaluation of introgression effects on agronomic performance.

Seed composition QTL from wild soybean were confirmed and validated in two genetic backgrounds across multiple environments, candidate genes were identified, and agronomic performance of backcross introgression lines was evaluated. Through selection for soybean yield, breeders have inadvertently reduced seed protein content and increased oil due to phenotypic and genetic correlations between these three traits. Therefore, identifying alleles that increase protein without adversely affecting oil and yield is of interest for breeders and the entire soybean value chain. Previously, a G. max × G. soja population was used to map a protein-associated region to ~ 4.6 Mbp on chromosome (Chr) 14. The G. soja allele significantly increased protein 6.5-7.2 g kg-1, without significantly decreasing oil. Additionally, two oil quantitative trait loci (QTL) were reported on Chrs 8 and 14. In this study, we aimed to confirm the Chr 14 protein QTL, evaluate QTL effects on seed composition and agronomic performance, and further fine-map to identify candidate genes. We validated and fine-mapped the Chr 14 protein QTL to a 0.6 Mbp region in a different genetic background, where the G. soja allele significantly increased protein by 9.3 g kg-1. Further, we confirmed the Chr 14 oil QTL linked to the protein QTL and the Chr 8 oil QTL. Chr 14 protein QTL effects on agronomic traits were evaluated in a backcross population across eight environments. The QTL significantly increased protein content, without significantly impacting oil, maturity, or plant height. While the QTL impacted yield and lodging, its effect and significance varied within environments. The candidate genes identified for these three validated seed composition QTL, along with additional molecular markers developed, offer valuable resources for improving seed composition in soybean breeding programs.

Quantitative Trait Loci↗

PubMed2002

Strain and sex differences in repeated ethanol treatment-induced motor activity in quasi-congenic mice.

The B6.C quasi-congenic Recombinant QTL Introgression (RQI) strains of the b4i5 series have similar genetic background, but differ in about 5% of their genome from the C57BL/6ByJ (B6) background strain because they carry short chromosome segments introgressed from the BALB/cJ (C) donor strain. These RQI strains were derived from mouse lines selectively bred for high activity of mesencephalic tyrosine hydroxylase (TH/MES), therefore genetic variation in dopamine system-related behaviours, such as ethanol-induced motor activity, can be expected. Males and females of 17 RQI and two progenitor strains were tested for initial motor activity for 15 min after a habituating injection of saline, which was followed by an i.p. injection of saline or ethanol (2 g/kg) and an additional test of motor activity for 30 min. This procedure was repeated during 4 subsequent days. In all strains, the first-day ethanol treatment showed an inhibitory effect. With repetition of the treatment the inhibitory effect decreased, and a stimulatory effect could be observed with significant strain- and sex-dependent variation. Females exhibited higher activity in the saline group than males, and reached an equilibrium of inhibition and stimulation sooner than males with repetition of the ethanol treatment. The highest (> 25-fold) difference in activity after repeated ethanol treatment was detected between females of the two strains B6.Cb4i5-Alpha4/Vad and B6.Cb4i5-Beta13/Vad. These results firstly suggest that females are more sensitive to repeated ethanol exposure than males, secondly they support the observations that ethanol has both inhibitory and stimulatory effects on motor activity, which are affected by sex, genotype, and repetition of treatment, and thirdly offer new quasi-congenic animal models with highly different responses to ethanol allowing one to more quickly move to gene detection.

Animals↗

PubMed2001

Cross-species amplification of the Hordeum chilense genome using barley sequence-tagged-sites (STSs).

A selection of 51 barley Sequence-Tagged Sites (STSs) were studied for their utility in Hordeum chilense. They included four primer sets from wheat origin and six primer sets from oat origin. Forty-four primer pairs amplified H. chilense products consistently. Five primer pairs were suitable for studying the introgression of H. chilense in wheat because they amplified H. chilense products of distinct size. Six of the STSs showed polymorphism between different H. chilense accessions. The results showed that barley STSs could be useful for the genetic characterization of H. chilense, tritordeums and derived introgression lines.

Avena↗

PubMed2002

Physical and genetic mapping in the grasses Lolium perenne and Festuca pratensis.

A single chromosome of the grass species Festuca pratensis has been introgressed into Lolium perenne to produce a diploid monosomic substitution line 2n = 2x = 14. In this line recombination occurs throughout the length of the F. pratensis/L. perenne bivalent. The F. pratensis chromosome and recombinants between it and its L. perenne homeologue can be visualized using genomic in situ hybridization (GISH). GISH junctions represent the physical locations of sites of recombination, enabling a range of recombinant chromosomes to be used for physical mapping of the introgressed F. pratensis chromosome. The physical map, in conjunction with a genetic map composed of 104 F. pratensis-specific amplified fragment length polymorphisms (AFLPs), demonstrated: (1) the first large-scale analysis of the physical distribution of AFLPs; (2) variation in the relationship between genetic and physical distance from one part of the F. pratensis chromosome to another (e.g., variation was observed between and within chromosome arms); (3) that nucleolar organizer regions (NORs) and centromeres greatly reduce recombination; (4) that coding sequences are present close to the centromere and NORs in areas of low recombination in plant species with large genomes; and (5) apparent complete synteny between the F. pratensis chromosome and rice chromosome 1.

Chromosomes, Plant↗

PubMed2000

Reinforcement and divergence under assortative mating.

Traits that cause assortative mating such as the flowering time in plants and body size in animals can produce reproductive isolation between hybridizing populations. Can selection against unfit hybrids cause two populations to diverge in their mean values for these kinds of traits? Here I present a haploid analytical model of one population that receives gene flow from another. The partial pre-zygotic isolation between the two populations is caused by assortative mating for a trait that is influenced by any number of genes with additive effects. The post-zygotic isolation is caused by selection against genetic incompatibilities that can involve any form of selection on individual genes and gene combinations (epistasis). The analysis assumes that the introgression rate and selection coefficients are small. The results show that the assortment trait mean will not diverge from the immigrants unless there is direct selection on the trait favouring it to do so or there are genes of very large effect. The amount of divergence at equilibrium is determined by a balance between direct selection on the assortment trait and introgression from the other population. Additional selection against hybrid genetic incompatibilities reduces the effective migration rate and allows greater divergence. The role of assortment in speciation is discussed in the light of these results.

Animals↗

PubMed2026

Genomic erosion in the assessment of species' extinction risk and recovery potential.

Many species are undergoing rapid population declines and environmental deterioration, leading to genomic erosion. Here we define genomic erosion as the loss of genetic diversity, accumulation of deleterious mutations, maladaptation, and introgression, all of which can undermine individual fitness and long-term population viability. Critically, this process continues even after demographic recovery due to a time-lagged impact of genetic drift, which is known as drift debt. Current conservation assessments, such as the International Union for Conservation of Nature Red List, focus on short-term extinction risk and do not capture the long-term consequences of genomic erosion. Likewise, the longer-term assessments of the International Union for Conservation of Nature Green Status may overestimate population recovery by failing to account for the enduring effects of genomic erosion. As genome sequencing becomes increasingly accessible, there is a growing opportunity to quantify genomic erosion and integrate it into conservation planning. Here, we use genomic simulations to illustrate how different genomic metrics are sensitive to the drift debt. We test how ancestral effective population size (Ne) and bottleneck history influence the tempo and severity of genomic erosion. Furthermore, we demonstrate how these dynamics shape genetic load and additive genetic variation, which are key indicators of long-term evolutionary potential. Finally, we present a proof-of-concept for a Genomic Green Status framework that aligns genomic metrics with conservation impact assessments, laying the foundation for genomics-informed strategies to support species recovery.

Extinction, Biological↗

PubMed2003

Transposable elements reveal the impact of introgression, rather than transposition, in Pisum diversity, evolution, and domestication.

The genetic structure and evolutionary history of the genus Pisum were studied exploiting our germplasm collection to compare the contribution of different mechanisms to the generation of diversity. We used sequence-specific amplification polymorphism (SSAP) markers to assess insertion site polymorphism generated by a representative of each of the two major groups of LTR-containing retrotransposons, PDR1 (Ty1/copia-like) and Cyclops (Ty3/gypsy-like), together with Pis1, a member of the En/Spm transposon superfamily. The analysis of extended sets of the four main Pisum species, P. fulvum, P. elatius, P. abyssinicum, and P. sativum, together with the reference set, revealed a distinct pattern of the NJ (Neighbor-Joining) tree for each basic lineage, which reflects the different evolutionary history of each species. The SSAP markers showed that Pisum is exceptionally polymorphic for an inbreeding species. The patterns of phylogenetic relationships deduced from different transposable elements were in general agreement. The retrotransposon-derived markers gave a clearer separation of the main lineages than the Pis1 markers and were able to distinguish the truly wild form of P. elatius from the antecedents of P. sativum. There were more species-specific and unique PDR1 markers than Pis1 markers in P. fulvum and P. elatius, pointing to PDR1 activity during speciation and diversification, but the proportion of these markers is low. The overall genetic diversity of Pisum and the extreme polymorphism in all species, except P. abyssinicum, indicate a high contribution of recombination between multiple ancestral lineages compared to transposition within lineages. The two independently domesticated pea species, P. abyssinicum and P. sativum, arose in contrasting ways from the common processes of hybridization, introgression, and selection without associated transpositional activity.

DNA Transposable Elements↗

PubMed2001

Evidence for broadscale introgressive hybridization between two redfish (genus Sebastes) in the North-west Atlantic: a rare marine example.

The evolutionary importance of introgressive hybridization has long been recognized by plant evolutionists, and there is now a growing recognition for its potential role in animals as well. Detailed empirical investigations of this evolutionary process, however, are still lacking in many animal groups, particularly in the marine environment. Using integrated microsatellite DNA data (eight loci analysed over 803 individuals representing 17 sampling locations) and multivariate statistical procedures (principal component, factorial correspondence and admixture proportion analyses), we: (i) provide a detailed dissection of the dynamics of introgressive hybridization between Sebastes fasciatus and S. mentella, two economically important redfishes from the North-west Atlantic; and (ii) infer the factors potentially involved in the maintenance of the hybrid zone observed in the gulf of St. Lawrence and south of Newfoundland. This study provided one of the rare examples of extensive introgressive hybridization in the ocean, and highlighted the predominant role of this process in shaping the extent of genetic diversity, interspecific differences and population structuring among redfishes from the North-west Atlantic. The extensive (average rate of introgression = 15%) but geographically circumscribed and asymmetrical pattern of introgressive hybridization, the sympatric persistence of two reproductively isolated introgressed groups, the differential patterns of linkage disequilibrium among samples, and the maintenance of genetic integrity of both species outside the defined zone of introgression despite high potential for gene flow, all implicated selection in promoting and maintaining the observed pattern of introgression.

Animals↗