SEARCH · PubMed Health

Results for “Introgression”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,513 records · Page 84Linked to original sources

PubMed2005

Cytology and fertility of viable hybrids of Nicotiana tabacum L. cv. TB-566 with N. alata Link et Otto.

A vigorous hybrid (N. tabacum cv. TB-566 tetra x N. alata) x N. alata was obtained by backcrossing a partly viable sesquidiploid hybrid N. tabacum cv. TB-566 tetra x N. alata to N. alata. The hybrid was a 35-chromosome near-amphihaploid with a pair of N. alata chromosomes in disomic condition. It was completely self- and cross-sterile and formed from 7 to 8 bivalents in pollen mother cells. By using stem pith culture, polyploidized regenerants were obtained from the 35-chromosome hybrid with somatic chromosome numbers from 65 to 70. These regenerants showed fairly regular meiosis with the number of bivalents in pollen mother cells ranging from 27.3 to 30.4. Irregularities in meiosis included a high number of univalents, aberrant tetrads, and a high frequency of micronuclei. The percentage of acetocarmine-stainable pollen ranged from 22.1 to 78.4. A 66-chromosome regenerant showed fairly regular meiosis and was self-fertile but could not be backcrossed to N. tabacum. This barrier seems to be caused by genic imbalance rather than irregularities of meiotic divisions. Hence transfer programs based on the introgression of entire linkage groups (sexual and somatic hybridization) seem to be of little use in the case of that species.

Chromosomes, Plant↗

PubMed2005

Colonization, dispersal, and hybridization influence phylogeography of North Atlantic sea urchins (Strongylocentrotus droebachiensis).

We used frequency-based and coalescent-based phylogeographic analysis of sea urchin (Strongylocentrotus droebachiensis) mitochondrial DNA (mtDNA) sequences and previously published microsatellite data to understand the relative influence of colonization and gene flow from older (north Pacific) and younger (northeast Atlantic) sea urchin populations on genetic variation in the northwest Atlantic. We found strong evidence of survival of northwestern Atlantic populations in local Pleistocene glacial refugia: most haplotypes were the same as or closely related to Pacific haplotypes, with deep gene genealogies that reflect divergence times within the northwestern Atlantic that are much older than the last glacial maximum. We detected gene flow across the North Atlantic in the form of haplotypes shared with or recently descended from European populations. We also found evidence of significant introgression of haplotypes from a closely related species (S. pallidus). The relative magnitude of gene flow estimated by coalescent methods (and the effective population size differences among oceanic regions) depended on the genetic marker used. In general, we found very small effective population size in the northeastern Atlantic and high trans-Arctic gene flow between the Pacific and northwestern Atlantic. Both analyses suggested significant back-migration to the Pacific. However, microsatellites more strongly reflected older Pacific migration (with similar effective population sizes across the Arctic), whereas mtDNA sequences appeared to be more sensitive to recent trans- Atlantic dispersal (with larger differences in effective population size). These differences across marker types might have several biological or methodological causes, and they suggest caution in interpretation of the results from a single locus or class of markers.

Animals↗

PubMed2005

Molecular tagging of gene conferring leaf blight resistance using microsatellites in sorghum [Sorghum bicolor (L.) Moench].

Resistance to leaf blight in sorghum [Sorghum bicolor (L.) Moench] accession G-118 was found to segregate as a single dominant trait in a cross to susceptible cultivar, HC-136. Molecular marker(s) linked to the locus for disease resistance was identified using simple sequence repeat (SSR) markers coupled with bulk segregant analysis. Genomic DNA from the parental cultivars and bulks were screened by PCR amplification with 50 simple sequence repeat primer pairs. Out of these, 38 SSR primers produced polymorphism between parents. After screening of these 38 SSRs with resistant and susceptible bulk, one SSR primer, Xtxp 309 produced a unique band of approximately 700 bp only in resistant parent and resistant bulk and a unique band of 450 bp only in susceptible parent and susceptible bulk. Upon screening with individual resistant and susceptible recombinant inbred lines (RILs), marker Xtxp 309 produced amplification in 23 of the 26 resistant RILs and no amplification was produced in any of the 25 susceptible RILs. The same marker Xtxp 309 produced amplification in 21 of the susceptible RILs and 3 of the resistant RILs of 450 bp band. This was found to be located at a distance of 3.12 cM away from the locus governing resistance to leaf blight which was considered to be closely linked and 7.95 cM away from the locus governing susceptibility to leaf blight. This marker may prove useful in MAS for gene introgression, plant genetic diagnostics and gene pyramiding for resistance via genetic transformation for disease resistance in plants.

Fungi↗

PubMed2003

[Accelerated improvement of bacterial blight resistance of 'Shuhui527' using molecular marker-assisted selection].

'Shuhui527' is a promising restorer line bred by Rice Research Institute of Sichuan Agricultural University in recent years. However, this line is susceptible to Bacterial Blight (BB), which limits its use. The IRBB60, from the International Rice Research Institute (IRRI), contains dominant genes Xa21 and Xa4 conferring resistance to BB. The objective of this study is to improve the BB resistance of 'Shuhui527' by introgressing Xa21 and Xa4, the two broad-spectrum BB resistance genes, into 'Shuhui527' with IRBB60 as the donor, pTA248 and MP12, linking tightly with Xa21 and Xa4 respectively as DNA markers. BC1 F1 progenies of (Shuhui527 x IRBB60), containing Xa21 and Xa4 identified using PCR screening and with agronomic traits including plant type, grain type and days to heading etc similar to those of 'Shuhui527', were subsequently backcrossed to 'Shuhui527' and self-pollinated to generate BC2 F1 and BC1 F2 . The BC3 F1 and BC3 F2 were subsequently developed using the same approach. Among the 20 BC3 F2 plants, homozygous Xa21 and Xa4,10 plants were the most similar to 'Shuhui527' in the agronomic traits, and were screened using 120 pairs SSR and 100 pairs RAPD markers. Based on the results of the background screening and the performance of the agronomic traits, 5 plants were identified as improved-'Shuhui527' and designated as 527R-5, 527R-6, 527R-8, 527R-9 and 527R-10. The improved-' Shuhui527' lines expressed high resistance to Xanthomonas oryzae pv . oryzae (Xoo) stains C I - C VII, P1 and P6. The evaluation of the polymorphisms and selection accuracies of pTA248 and MP12 demonstrated that the polymorphisms of the two markers were obvious and co-dominant and the accuracies were more than 97% and 83% respectively, indicating the two markers are good for Xa21 and Xa4 in Molecular Marker-assisted Selection.

Genes, Plant↗

PubMed2004

[Contribution of molecular phylogeny and morphometrics to the systematics of African elephants].

African elephants are conventionally classified as a single species: Loxodonta africana (Blumenbach 1797). However, the discovery in 1900 of a smaller form of the African elephant, spread throughout the equatorial belt of this land, has given rise to a debate over the relevance of a second species of elephant in Africa. The twentieth century has not provided any definite answer to this question. Actually, recent molecular analyses have sustained this issue by advocating either a division of forest elephants into a valid species, or their inclusion as a subspecies of L. africana. Our work initiated at the National Museum of Natural History of Paris provides new molecular (mitochondrial) and morphological (and morphometrical) evidence making it possible to propose a comprehensive phylogenetic hypothesis. It appears that there is no conclusive argument to keep forest elephants (cyclotis form) and savannah elephants (africana form) apart in two distinct species. A high level of mitochondrial introgression between the two forms, as well as a continuum in the morphology of the skulls of the two morphotypes rather suggests that, despite an ancient division, these two taxa freely interbreed wherever their ranges intersect. We thus adopt a conservative systematic position in considering these two forms as two subspecies, respectively: L. africana africana, the savannah elephant, and L. africana cyclotis, the forest elephant. We finally discuss the conservation topic in the light of this systematic framework.

Africa↗

PubMed2005

Genealogical footprints of speciation processes in wild tomatoes: demography and evidence for historical gene flow.

Multilocus studies assessing patterns of nucleotide polymorphism within and among closely related species provide access to genealogical information bearing on demographic and geographic aspects of their speciation history. However, the technical difficulties in obtaining sufficient sequence data have severely limited this approach thus far, especially in outbred plant taxa. We employ the analytical framework of divergence population genetics in testing the isolation model of speciation in three self-incompatible species of wild tomatoes (clade Lycopersicon), in particular the assumption of divergence without gene flow. Based on DNA sequence data for 13 nuclear loci, average levels of silent polymorphism vary more than three-fold among species. We estimate a large effective population size for the ancestral species, quite similar to that of the highly polymorphic L. peruvianum. The other two species, however, exhibit concordant signatures of population-size reduction. These demographic inferences are biologically plausible and consistent with results obtained from standard neutrality tests. While the isolation model cannot be rejected by goodness-of-fit criteria, patterns of intragenic linkage disequilibrium in L. peruvianum are indicative of historical introgression at least in some regions of the genome. Considered jointly with the geographic pattern of postzygotic reproductive isolation, our results suggest that speciation occurred under residual gene flow, implying natural selection as one of the evolutionary forces driving the diversification of tomato lineages.

Base Sequence↗

PubMed2005

Strong selection against hybrids at a hybrid zone in the Ensatina ring species complex and its evolutionary implications.

The analysis of interactions between lineages at varying levels of genetic divergence can provide insights into the process of speciation through the accumulation of incompatible mutations. Ring species, and especially the Ensatina eschscholtzii system exemplify this approach. The plethodontid salamanders E. eschscholtzii xanthoptica and E. eschscholtzii platensis hybridize in the central Sierran foothills of California. We compared the genetic structure across two transects (southern and northern Calaveras Co.), one of which was resampled over 20 years, and examined diagnostic molecular markers (eight allozyme loci and mitochondrial DNA) and a diagnostic quantitative trait (color pattern). Key results across all studies were: (1) cline centers for all markers were coincident and the zones were narrow, with width estimates of 730 m to 2000 m; (2) cline centers at the northern Calaveras transect were coincident between 1981 and 2001, demonstrating repeatability over five generations; (3) there were very few if any putative F1s, but a relatively high number of backcrossed individuals in the central portion of transects; and (4) we found substantial linkage disequilibrium in all three studies and strong heterozygote deficit both in northern Calaveras, in 2001, and southern Calaveras. Both linkage disequilibrium and heterozygote deficit showed maximum values near the center of the zones. Using estimates of cline width and dispersal, we infer strong selection against hybrids. This is sufficient to promote accumulation of differences at loci that are neutral or under divergent selection, but would still allow for introgression of adaptive alleles. The evidence for strong but incomplete isolation across this centrally located contact is consistent with theory suggesting a gradual increase in postzygotic incompatibility between allopatric populations subject to divergent selection and reinforces the value of Ensatina as a system for the study of divergence and speciation at multiple stages.

Animals↗

PubMed2005

Female sterility in hybrids between Anopheles gambiae and A. arabiensis, and the causes of Haldane's rule.

Although F1 female hybrids between Anopheles gambiae and A. arabiensis are fully fertile, sterility is present in backcross females. Here we report the results of a study into the genetic basis of backcross female sterility. Using 23 markers, we performed quantitative trait loci (QTL) mapping analyses to identify chromosomal regions involved in hybrid female sterility. We found that female sterility in backcrosses in both directions is primarily caused by interspecific interactions between a heterozygous X chromosome and recessive autosomal factors. In addition, our data provide support for two theories implicated in Haldane's rule in a single taxon. A comparison with data from a previous study shows that male hybrid sterility QTL are present in higher numbers than female hybrid sterility QTL. Furthermore, autosomal female sterility factors tend to be recessive, supporting the dominance theory for female sterility. Finally, our data indicate a very large effect of the X chromosome from both species on hybrid female sterility, despite the fact that the X chromosome represents less than 9% of the genome. However, this could be the result of a lack of introgression of the X chromosome between A. gambiae and A. arabiensis, rather than a faster evolution of sterility factors on the X chromosome.

Animals↗

PubMed2005

[Grain protein content in wheat: genetics of the character and some predictions for its improvement in common wheat].

The results of studies on genetic control of the grain protein content character in common wheat and the attempts of its improvement using traditional breeding approaches and methods of experimental mutagenesis and introgressive hybridization are presented. The evolution of the views on the genetic structure of the character is considered. Possible explanations are given to the fact that the attempts to significantly improve the character in question in common wheat cultivars have failed in spite of long-term genetic and selection studies. Possible lines of further investigation of genetic control of grain protein content and its increase in common wheat are discussed.

Crops, Agricultural↗

PubMed2005

[Hybrid and monosomic analyses of smoky coloration of the ear in common wheat].

The results of the hybrid and monosomic analyses of smoky ear coloration in the common wheat variety columbina are reported. The character has been found to be monogenic, and its gene has been located to chromosome IDS. The smoky ear coloration is determined by an allele of gene Rg2 introgressed to wheat from Aegilops tauschii.

Alleles↗

PubMed2005

[Developing single segment substitution lines (SSSLs) in rice (Oryza sativa L.) using advanced backcrosses and MAS].

A novel population consisted of 86 single segment substitution lines (SSSLs) were developed from advanced backcrosses between the recipient, Huajingxian 74 and six donors by microsatellite marker-assisted selection (MAS). Fifty-two SSSLs were selected in BC3F2, and 34 others were selected in BC3F3. Every SSSL contains a single chromosome segment introgressed from one donor on the genetic background of Huajingxian 74. The substituted segments in SSSLs were distributed on 12 rice chromosomes. The estimated length of the substituted segments in SSSLs ranged from 1.5 cM to 56.3 cM with an average of 23.0 cM. Total of the substituted segments covered 57.1% of the rice genome.

Chromosome Mapping↗

PubMed2005

Identification of a rice gene (Bph 1) conferring resistance to brown planthopper (Nilaparvata lugens Stal) using STS markers.

This study was carried out to identify a high-resolution marker for a gene conferring resistance to brown planthopper (BPH) biotype 1, using japonica type resistant lines. Bulked segregant analyses were conducted using 520 RAPD primers to identify RAPD fragments linked to the BPH resistance gene. Eleven RAPDs were shown to be polymorphic amplicons between resistant and susceptible progeny. One of these primers, OPE 18, which amplified a 923 bp band tightly linked to resistance, was converted into a sequence-tagged-site (STS) marker. The STS marker, BpE18-3, was easily detectable as a dominant band with tight linkage (3.9cM) to Bph1. It promises to be useful as a marker for assisted selection of resistant progeny in backcross breeding programs to introgress the resistance gene into elite japonica cultivars.

Animals↗

PubMed1992

Plant protoplasts as genetic tool: selectable markers for developmental studies.

Protoplasts have usually been presented as a methodological tool. Even as such, they make possible an impressive array of applications in plant biology. Here we report on the use of protoplast-derived selectable markers in the study of several disturbed genetic systems with obvious effects on plant development: (1) auxotrophic mutants and the control of amino acid biosynthesis and transport in vegetative and reproductive tissues; (2) introgression of alien genetic information across phylogenetic boundaries by protoplast fusion, a consequence of controlled dedifferentiation-redifferentiation processes and attenuated incompatibility reactions in cultured cells; (3) expression (in)stability of foreign genes in transgenic plants during successive meiotic generations and in crosses between independent transformants.

Cells, Cultured↗

PubMed2005

[Genetic analysis of anthocyanin of the anthers and culm pigmentation in common wheat].

Anthocyanin pigmentation of various organs develops during plant ontogeny in response to adverse and damaging abiotic and biotic stressors (environmental factors). Using the monosome method, the genes responsible for anther and culm anthocyanin pigmentation (Pan1 and Pc2, respectively) were localized to 7D chromosome in introgressive lines from crosses between common wheat Triticum aestivum L. and the species Triticum timopheevii Zhuk. Genetic analysis of ten common wheat genotypes using testers carrying genes Pan1, Pn1, and Pn2 showed that these genotypes contained Pan1 and Pn2 genes. Visual examination of plants from 70 and 76 varieties of respectively winter and spring common wheat revealed anthocyanin pigmentation of anthers and culms in 36 varieties. Pan1 and Pn2 genes were presumably introduced into common wheat from Aegilops tauschii (Fig.) Tzvel., a donor of the D genome.

Chromosomes, Plant↗

PubMedDate not supplied

[Genetic structure of the spawning population of Danube shad, Alosa pontica, Eichwaldt 1838 (Clupeiformes, Alosiinae)].

The genetic structure of the population of Danube shad, Alosa pontica, has been studied by means of analysis of 3 polymorphic biochemical gene loci. The results of the study provide evidence of its genetic heterogeneity which is expressed by: firstly, an unbalanced ratio of genotype loci manifested by an excess of rare homozygotes and deficite of the correspoding heterozygotes, and secondly, differences in the allele frequencies between shad populations arriving for spawning in March-April and May-June. It is suggested that there could be two causes of heterogeneity: one due to the introgressive hybridization between various forms of A. pontica and another to the differences between early and late spring races of shad which to a certain extent are reproductively autonomous.

Alleles↗

PubMed2006

[Cytogenetic analysis of alloplasmic recombinant lines (H. vulgare)-T. aestivum with unstable fertility and viability].

Comparative cytogenetic analysis was performed with four alloplasmic recombinant (Hordeum vulgare)-Triticum aestivum lines differing in morphological traits, number of seeds per spike, and seed plumpness. None of the lines displayed introgression of the barley genetic material: the karyotypes included only common wheat chromosomes. Two lines, 79(B) and 79(D), were cytogenetically stable. Plants of lines 79(A) and 79(C) displayed a high frequency of unbalanced chromosome aberrations, including dicentric and polycentric chromosomes, terminal deletions varying in size, acentric fragments, and multiple unidentifiable translocations. Previous studies of the mitochondrial genome showed that the two cytologically unstable lines, which were also unstable in fertility and viability, are characterized by heteroplasmy at the mitochondrial 18S-5S locus (simultaneous presence of barley and wheat fragments). Stable lines 79(B) and 79(D) with normal fertility contained only wheat mitochondrial markers. It was assumed that the substantial instability of the nuclear genome in lines 79(C) and 79(A) was a result of nuclear-cytoplasmic incompatibility and was associated with heteroplasmy, while elimination or considerable reduction of barley material in the mitochondrial genome stabilized the nuclear genome of lines 79(B) and 79(D). In turn, the instability of the nuclear genome was responsible for a decrease in viability and fertility of plants.

Chimera↗

PubMed2006

Hybridization of Bombina bombina and B. variegata (Anura, Discoglossidae) at a sharp ecotone in western Ukraine: comparisons across transects and over time.

Bombina bombina and B. variegata are two anciently diverged toad taxa that have adapted to different breeding habitats yet hybridize freely in zones of overlap where their parapatric distributions meet. Here, we report on a joint genetic and ecological analysis of a hybrid zone in the vicinity of Stryi in western Ukraine. We used five unlinked allozyme loci, two nuclear single nucleotide polymorphisms and a mitochondrial DNA haplotype as genetic markers. Parallel allele frequency clines with a sharp central step occur across a sharp ecotone, where transitions in aquatic habitat, elevation, and terrestrial vegetation coincide. The width of the hybrid zone, estimated as the inverse of the maximum gradient in allele frequency, is 2.3 km. This is the smallest of four estimates derived from different clinal transects across Europe. We argue that the narrow cline near Stryi is mainly due to a combination of habitat distribution and habitat preference. Adult toads show a preference for either ponds (B. bombina) or puddles (B. variegata), which is known to affect the distribution of genotypes within the hybrid zones. At Stryi, it should cause a reduction of the dispersal rate across the ecotone and thus narrow the cline. A detailed comparison of all five intensively studied Bombina transects lends support to the hypothesis that habitat distribution plus habitat preference can jointly affect the structure of hybrid zones and, ultimately, the resulting barriers to gene flow between differentiated gene pools. This study also represents a resampling of an area that was last studied more than 70 years ago. Our allele-frequency clines largely coincide with those that were described then on the basis of morphological variation. However, we found asymmetrical introgression of B. variegata genes into B. bombina territory along the bank of a river.

Animals↗

PubMed2006

Cyto-nuclear epistasis: two-locus random genetic drift in hermaphroditic and dioecious species.

We report the findings of our theoretical investigation of the effect of random genetic drift on the covariance of identity-by-descent (ibd) of nuclear and cytoplasmic genes. The covariance in ibd measures of the degree to which cyto-nuclear gene combinations are heritable, that is, transmitted together from parents to offspring. We show how the mating system affects the covariance of ibd, a potentially important aspect of host-pathogen or host-symbiont coevolution. The magnitude of this covariance influences the degree to which the evolution of apparently neutral cytoplasmic genes, often used in molecular phylogenetics, might be influenced by selection acting on unlinked nuclear genes. To the extent that cyto-nuclear gene combinations are inherited together, genomic conflict is mitigated and intergenomic transfer it facilitated, because genes in both organelle and nuclear genomes share the same evolutionary fate. The covariance of ibd also affects the rate at which cyto-nuclear epistatic variance is converted to additive variance necessary for a response to selection. We find that conversion is biased in species with separate sexes, so that the increment of additive variance added to the nuclear genome exceeds that added to the cytoplasmic genome. As a result, the host might have an adaptive advantage in a coevolutionary arms race with vertically (maternally) transmitted pathogens. Similarly, the nuclear genome could be a source of compensatory mutations for its organellar genomes, as occurs in cytoplasmic male sterility in some plant species. We also discuss the possibility that adaptive cytoplasmic elements, such as favorable mitochondrial mutations or endosymbionts (e.g., Wolbachia), have the potential to release heritable nuclear variation as they sweep through a host population, supporting the view that cytoplasmic introgression plays an important role in adaptation and speciation.

Alleles↗