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At least 55 records · Page 3Linked to original sources
PubMed1992

Identification of an S-locus glycoprotein allele introgressed from B. napus ssp. rapifera to B. napus ssp. oleifera.

Self-incompatible Brassica napus ssp. oleifera lines were generated by introgressing the S-locus from the self-incompatible B. napus ssp. rapifera Z line into the self-compatible cultivars, Topas and Regent, resulting in T2 and R2, respectively. Screening of a cDNA library made from R2 stigma RNA produced several candidate SLG (S-locus glycoprotein) cDNAs. One of the cDNAs, A14, was found to be represented in only the R2, T2 and Z lines. In addition, the corresponding A14 gene was demonstrated to segregate with the T2 self-incompatibility phenotype in an F2 population derived from a cross between T2 and Topas, and to exhibit high mRNA levels in the stigmas prior to anthesis. Sequence analysis of the A14 cDNA revealed close homology to B. oleracea SLG alleles associated with a Class I high activity self-incompatibility phenotype.

Alleles↗
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↗
PubMed1989

Genetic analysis of an interspecific hybrid swarm of Populus: occurrence of unidirectional introgression.

Restriction fragment length polymorphisms were used to distinguish genotypes of two species of Populus, P. fremontii ('Fremont') and P. angustifolia ('narrowleaf'). Both inter- and intraspecific polymorphisms were detected in these cottonwood trees. The interspecific variation was much greater than the intraspecific variation. This permitted identification of parental genotypes within individual trees of a hybrid swarm which exists in an overlap zone between the two species. Within this hybrid swarm, individual trees are either F1 hybrids or backcrosses with a pure 'narrowleaf' parent; no progeny were found that could be attributed to crossing between F1 hybrid trees, or to backcrossing between F1 hybrid trees and 'Fremont'.

Crosses, Genetic↗
PubMed1987

Alcohol-preferring (AA) and alcohol-avoiding (ANA) lines of rats after introgression of alien genes.

Outcrossing has been used as a method for introducing new genetic variability into the high-drinking AA and low-drinking ANA rat lines that had reached their selection limits and were suffering of poor fertility and decreased litter size. The response to the renewed selection for differential alcohol consumption, and the effect of outcrossing upon the components of productivity are reported.

Alcohol Drinking↗
PubMed1988

[Genetic analysis of the hybridization zone between two subspecies Mus musculus domesticus and Mus musculus musculus in Bulgaria].

The hybrid zone between the two subspecies of mice Mus musculus domesticus and Mus musculus musculus, which has been studied extensively in Denmark, crosses Europe to the Black Sea through the Alps and the Balkans. Two hundred and seventy-nine animals were captured in 22 localities along a transect across the Balkans. The animals were characterized for seven diagnostic nuclear loci by protein electrophoresis and by restriction pattern analysis of their mitochondrial DNA. The nuclear data show a sharp transition between the two subspecies, most of the variations in allele frequencies (from 0.9 to 0.1) occurring within a 36-km section of the transect. The introgression varies from one locus to the other and is more pronounced, in terms of distance, in M. m. musculus territory. Mitochondrial DNA introgression is important but occurs in one direction only, i.e. from M. m. musculus to M. m. domesticus, while a cytoplasmic transfer from M. m. domesticus to M. m. musculus has been reported. A previous study showed that no Y chromosome introgression occurs. The different behaviour of these three types of markers could be due to the interaction between selection against hybrid genomes and meiotic recombination. Objectively, it would appear that the genes that can introgress are neutral or nearly so and have been separated from deleterious genes they were linked to by recombination. This could explain the differential introgression between autosomal loci. The mitochondrial and Y chromosomes undergo no or very little recombination and each is transmitted as a whole. Their degree of introgression is thus indicative of the intensity of selection resulting from the amount of functional differentiation between the two taxa, which seems to be strong for the Y chromosome and weak for mitochondrial DNA. We propose that the asymmetry of nuclear introgression is due to different population structures. As M. m. musculus is relatively less structured, the rapid spreading of introgressed genes would be favoured. Such a scheme, however, can hardly account for the unidirectionality of the mitochondrial flow, which could be due to sex-dependent behaviour.

Alleles↗
PubMed2025

A colorful legacy of hybridization in wood-warblers includes frequent sharing of carotenoid genes among species and genera.

Introgression between species has the potential to shape evolutionary trajectories in important ways, but uncovering complex introgression dynamics has only recently been made possible by advances in genomics. Warblers of the avian family Parulidae exemplify rapid diversification and sexual trait divergence, and we endeavored to study historical introgression in the family. We sequenced multiple genomes of nearly every species, constructed a phylogeny for the family, and investigated gene flow across the genome and at genes known for controlling feather color. We found that DNA haplotypes including the gene BCO2, which encodes an enzyme that degrades yellow carotenoids, have spread among genera multiple times-from Vermivora to Geothlypis and from Leiothlypis to multiple Cardellina and Setophaga species. Patterns of inheritance in the latter case point to introgression that occurred 0.5 to 2 million years ago, and the shared haplotype among recipient species is less than 100 nucleotides long. Separately, we found evidence of introgression from red Cardellina species to both of the two red Myioborus species at BDH1L and from one red Myioborus species to the other at CYP2J19; both are key genes in the pathway that converts yellow carotenoids to red ketocarotenoids. Our results show that introgression is a common mechanism for the evolution of colorful plumage in parulid warblers and hint at complex histories of gene flow behind some of the Western Hemisphere's most colorful birds.

Animals↗
PubMed2024

Interspecific transfer of genetic information through polyploid bridges.

Hybridization blurs species boundaries and leads to intertwined lineages resulting in reticulate evolution. Polyploidy, the outcome of whole genome duplication (WGD), has more recently been implicated in promoting and facilitating hybridization between polyploid species, potentially leading to adaptive introgression. However, because polyploid lineages are usually ephemeral states in the evolutionary history of life it is unclear whether WGD-potentiated hybridization has any appreciable effect on their diploid counterparts. Here, we develop a model of cytotype dynamics within mixed-ploidy populations to demonstrate that polyploidy can in fact serve as a bridge for gene flow between diploid lineages, where introgression is fully or partially hampered by the species barrier. Polyploid bridges emerge in the presence of triploid organisms, which despite critically low levels of fitness, can still allow the transfer of alleles between diploid states of independently evolving mixed-ploidy species. Notably, while marked genetic divergence prevents polyploid-mediated interspecific gene flow, we show that increased recombination rates can offset these evolutionary constraints, allowing a more efficient sorting of alleles at higher-ploidy levels before introgression into diploid gene pools. Additionally, we derive an analytical approximation for the rate of gene flow at the tetraploid level necessary to supersede introgression between diploids with nonzero introgression rates, which is especially relevant for plant species complexes, where interspecific gene flow is ubiquitous. Altogether, our results illustrate the potential impact of polyploid bridges on the (re)distribution of genetic material across ecological communities during evolution, representing a potential force behind reticulation.

Polyploidy↗
PubMed2026

Archaic ancestry inference in imputed ancient human genomes.

When modern humans expanded from Africa into Eurasia, they interbred with archaic hominins such as Neanderthals and Denisovans. This introgression shaped human evolution, yet most insights have been gained from present-day genomes, leaving little known about how archaic variants evolved after interbreeding. Ancient genomes offer a direct view of this process, but low coverage and poor quality have limited their use. Recent advances in genotype imputation offer a way to overcome these challenges by reconstructing missing information from reference panels and recovering evolutionary signals from low-coverage data. Here, we show that imputation enables accurate detection and quantification of archaic introgression in ancient genomes, improves local archaic ancestry inference, and that regions of archaic ancestry are imputed with especially high accuracy. We further demonstrate that imputed genomes can reconstruct the trajectories of introgressed haplotypes, distinguish populations across time and geography, and identify both known and additional candidates for adaptive introgression.

Humans↗
PubMed2025

Are We Witnessing a Speciation Continuum? Evidence From Current and Past Gene Flow in the Genus Oritrophium s.s. (Asteraceae) From the Tropical High Andes.

Determining species boundaries is key for appropriately assessing biodiversity. However, the continuity of the speciation process makes delimiting species a difficult task, especially for recently diverged taxa. Furthermore, past introgression may leave traces that result in reticulate evolutionary patterns, challenging the estimation of species relationships. The fastest-evolving biodiversity hotspot on Earth is the Páramo. Its flora in the tropical high Andes is known for extraordinarily high species richness and endemism. However, the recent origin, fast diversification and complex taxonomy of many genera challenge species delimitation and phylogenetic reconstruction. In this study, we reconstructed phylogenetic relationships and addressed the role of introgression in the diversification of Oritrophium s.s. (Asteraceae) based on phylogenomic data. We combined genomic, phenotypic and ecological data to test species boundaries and compared trajectories across the speciation continuum within the taxonomically complex 'O. peruvianum group'. We found that historical introgression played an important role in the evolution of Oritrophium s.s., and many of the taxa within the 'O. peruvianum group' are at various stages of speciation. These results highlight the importance of testing for introgression to understand the diversification of recently evolved groups. Likewise, they suggest that heterogeneous speciation trajectories associated with geographic isolation and secondary contact, possibly during the Pleistocene, contributed to plant diversity in the tropical high Andes.

Genetic Speciation↗
PubMed1991

The evolutionary history of Drosophila buzzatii. XXI. Cumulative action of multiple sterility factors on spermatogenesis in hybrids of D. buzzatii and D. koepferae.

The genetic basis of sterility in male hybrids of Drosophila buzzatii and D. koepferae has been investigated by assessment of the effects on spermatogenesis of substituting separate chromosome segments of the recipient species with the homologous material from the donor species, either in heterozygous (autosomes) or hemizygous (X chromosome) condition, after successive backcrossing of hybrid females to either parental species. Introgressed segments were identified by the characteristic asynapsis of the polytene chromosomes in their heterospecific regions. Except for one case, the introgression of chromosome segments either from autosome 3, 4, or 5 brings about sterility only when the introgressed segment exceeds a minimum size (threshold size). Segments of equal size frequently produce similar abnormalities, whose severity increases with the size of the introgressed segment. Apparently, throughout these autosomes of D. buzzatii and D. koepferae there are many non-allelic, minor sterility genes, whose individual segregation cannot be recognized phenotypically, and which act cumulatively on the same characteristics of spermatogenesis, each contributing a small effect to the phenotype. Accordingly, these genes should be considered as polygenes, and the type of sterility they bring about should be properly designated polygenic sterility.

Animals↗
PubMed2026

The curious case of sporadic nematode susceptibility in "Tifguard" peanut (Arachis hypogaea): seed mixture or genetic instability?

The Runner-type peanut (Arachis hypogaea L.) cultivar "Tifguard" carries an introgressed chromosomal segment on chromosome A09 from A. cardenasii that confers resistance to root-knot nematode (RKN). Despite this, a proportion of "Tifguard" plants show RKN symptoms, which could plausibly be attributed to seed mixture or outcrossing. However, recent work has shown that cultivated peanut exhibits surprisingly frequent large-scale chromosomal instability (1% to 5%); suggesting that resistance loss could arise from spontaneous structural genomic change. To test these possibilities, we grew foundation seed in an RKN-infested field and collected symptomatic and asymptomatic plants. Lineages derived by single-seed descent were genotyped using the Axiom Arachis 48K SNP array v2 and whole-genome sequencing. Symptomatic lineages lacked the A. cardenasii introgression on chromosome A09 and instead carried the complete endogenous A. hypogaea A09 region at the expected dosage. There was no evidence of large-scale homoeologous exchange, deletion, or other genomic instability affecting this chromosome. Most susceptible plants were closely related to resistant "Tifguard" but lacked the A09 introgression, with a smaller proportion assignable to known nematode-susceptible cultivars, implicating seed mixture with a possible contribution from cross-pollination rather than genomic instability. Because resistance depends on a single major-effect segment, rare events have disproportionate phenotypic impact, placing high demands on genetic purity. For important traits conferred by major loci, marker-based testing across seed-increase stages could verify trait retention directly, and is increasingly practical as marker costs decline.

Arachis↗
PubMed1992

Genetic and physical analysis of the rice bacterial blight disease resistance locus, Xa21.

Nearly isogenic lines (NILs) of rice (Oryza sativa) differing at a locus conferring resistance to the pathogen Xanthomonas oryzae pv. oryzae were surveyed with 123 DNA markers and 985 random primers using restriction fragment length plymorphism (RFLP) and random amplified polymorphic DNA (RAPD) analysis. One chromosome 11 marker (RG103) detected polymorphism between the NILs that cosegregated with Xa21. All other chromosome 11 DNA markers tested were monomorphic between the NILs, localizing the Xa21 introgressed region to an 8.3 cM interval on chromosome 11. Furthermore, we identified two polymerase chain reaction (PCR) products (RAPD2148 and RAPD818) that detected polymorphisms between the NILs. Genomic sequences hybridizing with RAPD818, RAPD248 and RG103 were duplicated specifically in the Xa21 NIL. All three markers cosegregated with the resistance locus, Xa21, in a F2 population of 386 progeny. Based on the frequency with which we recovered polymorphic Xa21-linked markers, we estimated the physical size of the introgressed region to be approximately 800 kb. This estimation was supported by physical mapping (using pulsed field gel electrophoresis) of the sequences hybridizing with the three Xa21-linked DNA markers. The results showed that the three Xa21-linked markers are physically close to each other, with one copy of the RAPD818 sequences located within 60 kb of RAPD248 and the other copy within 270 kb of RG103. None of the enzymes tested generated a DNA fragment that hybridized with all three of the markers indicating that the introgressed region containing the resistance locus Xa21 is probably larger than 270 kb.

Chromosome Mapping↗