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 1,117 records · Page 62Linked to original sources

PubMed1998

Analysis of natural allelic variation at flowering time loci in the Landsberg erecta and Cape Verde Islands ecotypes of Arabidopsis thaliana.

We have analyzed the flowering behavior of two Arabidopsis ecotypes: the laboratory strain Landsberg erecta (Ler) and an ecotype from the tropical Cape Verde Islands (Cvi). They differ little in their flowering phenotypes and in their responses to photoperiod length changes and to vernalization treatment. However, segregating populations derived from crosses between them showed a much larger variation. An approach of quantitative trait locus (QTL) mapping in recombinant inbred lines (RILs) grown under three environments differing in day-length and/or vernalization treatment has been used to detect and locate flowering loci. Four main QTLs were identified, designated early day-length insensitive (EDI), flowering F, G, and H (FLF, FLG, and FLH, respectively), to which most of the flowering behavior differences could be attributed. To further characterize the individual loci, near isogenic lines were constructed by introgressing Cvi early alleles of EDI and FLH into the Ler genetic background. EDI-Cvi alleles produce earliness under both long- and short-day photoperiods, rendering Ler plants almost day-length neutral. In addition, RILs were selected to analyze FLF and FLG. These loci interact epistatically and RILs carrying late alleles at FLF and FLG were very responsive to vernalization and showed an increased response to photoperiod length changes. The possible role of these loci for the control of flowering is discussed in the context of the current Arabidopsis model.

Alleles↗

PubMed1998

Multiple origins of cytologically identical chromosome inversions in the Anopheles gambiae complex.

For more than 60 years, evolutionary cytogeneticists have been using naturally occurring chromosomal inversions to infer phylogenetic histories, especially in insects with polytene chromosomes. The validity of this method is predicated on the assumption that inversions arise only once in the history of a lineage, so that sharing a particular inversion implies shared common ancestry. This assumption of monophyly has been generally validated by independent data. We present the first clear evidence that naturally occurring inversions, identical at the level of light microscopic examination of polytene chromosomes, may not always be monophyletic. The evidence comes from DNA sequence analyses of regions within or very near the breakpoints of an inversion called the 2La that is found in the Anopheles gambiae complex. Two species, A. merus and A. arabiensis, which are fixed for the "same" inversion, do not cluster with each other in a phylogenetic analysis of the DNA sequences within the 2La. Rather, A. merus 2La is most closely related to strains of A. gambiae homozygous for the 2L+. A. gambiae and A. merus are sister taxa, the immediate ancestor was evidently homozygous 2L+, and A. merus became fixed for an inversion cytologically identical to that in A. arabiensis. A. gambiae is polymorphic for 2La/2L+, and the 2La in this species is nearly identical at the DNA level to that in A. arabiensis, consistent with the growing evidence that introgression has or is occurring between these two most important vectors of malaria in the world. The parallel evolution of the "same" inversion may be promoted by the presence of selectively important genes within the breakpoints.

Animals↗

PubMed1999

Linkage analysis of molecular markers and quantitative trait loci in populations of inbred backcross lines of Brassica napus L.

Backcross populations are often used to study quantitative trait loci (QTL) after they are initially discovered in balanced populations, such as F(2), BC(1), or recombinant inbreds. While the latter are more powerful for mapping marker loci, the former have the reduced background genetic variation necessary for more precise estimation of QTL effects. Many populations of inbred backcross lines (IBLs) have been developed in plant and animal systems to permit simultaneous study and dissection of quantitative genetic variation introgressed from one source to another. Such populations have a genetic structure that can be used for linkage estimation and discovery of QTL. In this study, four populations of IBLs of oilseed Brassica napus were developed and analyzed to map genomic regions from the donor parent (a winter-type cultivar) that affect agronomic traits in spring-type inbreds and hybrids. Restriction fragment length polymorphisms (RFLPs) identified among the IBLs were used to calculate two-point recombination fractions and LOD scores through grid searches. This information allowed the enrichment of a composite genetic map of B. napus with 72 new RFLP loci. The selfed and hybrid progenies of the IBLs were evaluated during two growing seasons for several agronomic traits. Both pedigree structure and map information were incorporated into the QTL analysis by using a regression approach. The number of QTL detected for each trait and the number of effective factors calculated by using biometrical methods were of similar magnitude. Populations of IBLs were shown to be valuable for both marker mapping and QTL analysis.

Brassica↗

PubMed2000

Identification of heading date quantitative trait locus Hd6 and characterization of its epistatic interactions with Hd2 in rice using advanced backcross progeny.

A backcrossed population (BC(4)F(2)) derived from a cross between a japonica rice variety, Nipponbare, as the recurrent parent and an indica rice variety, Kasalath, as the donor parent showed a long-range variation in days to heading. Quantitative trait loci (QTL) analysis revealed that two QTL, one on chromosome 3, designated Hd6, and another on chromosome 2, designated Hd7, were involved in this variation; and Hd6 was precisely mapped as a single Mendelian factor by using progeny testing (BC(4)F(3)). The nearly isogenic line with QTL (QTL-NIL) that carries the chromosomal segment from Kasalath for the Hd6 region in Nipponbare's genetic background was developed by marker-assisted selection. In a day-length treatment test, the QTL-NIL for Hd6 prominently increased days to heading under a 13.5-hr day length compared with the recurrent parent, Nipponbare, suggesting that Hd6 controls photoperiod sensitivity. QTL analysis of the F(2) population derived from a cross between the QTL-NILs revealed existence of an epistatic interaction between Hd2, which is one of the photoperiod sensitivity genes detected in a previous analysis, and Hd6. The day-length treatment tests of these QTL-NILs, including the line introgressing both Hd2 and Hd6, also indicated an epistatic interaction for photoperiod sensitivity between them.

Chromosome Mapping↗

PubMed2001

Mapping of avirulence genes in Phytophthora infestans with amplified fragment length polymorphism markers selected by bulked segregant analysis.

In this study we investigated the genetic control of avirulence in the diploid oomycete pathogen Phytophthora infestans, the causal agent of late blight on potato. The dominant avirulence (Avr) genes matched six race-specific resistance genes introgressed in potato from a wild Solanum species. AFLP markers linked to Avr genes were selected by bulked segregant analysis and used to construct two high-density linkage maps, one containing Avr4 (located on linkage group A2-a) and the other containing a cluster of three tightly linked genes, Avr3, Avr10, and Avr11 (located on linkage group VIII). Bulked segregant analysis also resulted in a marker linked to Avr1 and this allowed positioning of Avr1 on linkage group IV. No bulked segregant analysis was performed for Avr2, but linkage to a set of random markers placed Avr2 on linkage group VI. Of the six Avr genes, five were located on the most distal part of the linkage group, possibly close to the telomere. The high-density mapping was initiated to facilitate future positional cloning of P. infestans Avr genes.

Chromosome Mapping↗

PubMed2002

Genetic analyses of endoreduplication in Zea mays endosperm: evidence of sporophytic and zygotic maternal control.

Flow cytometry was used to assess the variability of endoreduplication in endosperms of maize inbred lines. Little variation was found between midwestern dent types, and high levels of endoreduplication were observed in popcorns. Endoreduplication is different between inbred lines by 13-18 days after pollination, and flow cytometric analysis of ploidy level was feasible until 20 DAP. To study the genetic regulation of endoreduplication, four inbreds were crossed to B73 and developing endosperms from both parental, reciprocal F(1), and backcross generations were subjected to flow cytometric analysis. Three measurements of endoreduplication were calculated from these data and analyzed as quantitative genetic traits. Multiple models of trait inheritance were considered including triploid, diploid, sporophytic maternal, and maternal and paternal zygotic nuclear inheritance. Maternal zygotic effects, often considered a form of parental imprinting, and maternal sporophytic effects were detected. To test the feasibility of introgressing a high endoreduplication phenotype into a midwestern dent inbred line, a backcross population was generated from B73 x Sg18. Parental and progeny endoreduplication levels were compared and heritabilities assessed. The heritabilities calculated from these data generally agree with the values calculated in the larger crossing experiments.

Analysis of Variance↗

PubMed2002

A demonstration of a 1:1 correspondence between chiasma frequency and recombination using a Lolium perenne/Festuca pratensis substitution.

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. The chromatin of F. pratensis and L. perenne can be distinguished by genomic in situ hybridization (GISH), and it is therefore possible to visualize the substituted F. pratensis chromosome in the L. perenne background and to study chiasma formation in a single marked bivalent. Recombination occurs freely in the F. pratensis/L. perenne bivalent, and chiasma frequency counts give a predicted map length for this bivalent of 76 cM. The substituted F. pratensis chromosome was also mapped with 104 EcoRI/Tru91 and HindIII/Tru91 amplified fragment length polymorphisms (AFLPs), generating a marker map of 81 cM. This map length is almost identical to the map length of 76 cM predicted from the chiasma frequency data. The work demonstrates a 1:1 correspondence between chiasma frequency and recombination and, in addition, the absence of chromatid interference across the Festuca and Lolium centromeres.

Chromosome Mapping↗

PubMed2002

A molecular cytogenetic map of sorghum chromosome 1. Fluorescence in situ hybridization analysis with mapped bacterial artificial chromosomes.

We used structural genomic resources for Sorghum bicolor (L.) Moench to target and develop multiple molecular cytogenetic probes that would provide extensive coverage for a specific chromosome of sorghum. Bacterial artificial chromosome (BAC) clones containing molecular markers mapped across sorghum linkage group A were labeled as probes for fluorescence in situ hybridization (FISH). Signals from single-, dual-, and multiprobe BAC-FISH to spreads of mitotic chromosomes and pachytene bivalents were associated with the largest sorghum chromosome, which bears the nucleolus organizing region (NOR). The order of individual BAC-FISH loci along the chromosome was fully concordant to that of marker loci along the linkage map. In addition, the order of several tightly linked molecular markers was clarified by FISH analysis. The FISH results indicate that markers from the linkage map positions 0.0-81.8 cM reside in the short arm of chromosome 1 whereas markers from 81.8-242.9 cM are located in the long arm of chromosome 1. The centromere and NOR were located in a large heterochromatic region that spans approximately 60% of chromosome 1. In contrast, this region represents only 0.7% of the total genetic map distance of this chromosome. Variation in recombination frequency among euchromatic chromosomal regions also was apparent. The integrated data underscore the value of cytological data, because minor errors and uncertainties in linkage maps can involve huge physical regions. The successful development of multiprobe FISH cocktails suggests that it is feasible to develop chromosome-specific "paints" from genomic resources rather than flow sorting or microdissection and that when applied to pachytene chromatin, such cocktails provide an especially powerful framework for mapping. Such a molecular cytogenetic infrastructure would be inherently cross-linked with other genomic tools and thereby establish a cytogenomics system with extensive utility in development and application of genomic resources, cloning, transgene localization, development of plant "chromonomics," germplasm introgression, and marker-assisted breeding. In combination with previously reported work, the results indicate that a sorghum cytogenomics system would be partially applicable to other gramineous genera.

Chromosome Mapping↗

PubMed2002

The genetic basis of the interspecific differences in wing size in Nasonia (Hymenoptera; Pteromalidae): major quantitative trait loci and epistasis.

There is a 2.5-fold difference in male wing size between two haplodiploid insect species, Nasonia vitripennis and N. giraulti. The haploidy of males facilitated a full genomic screen for quantitative trait loci (QTL) affecting wing size and the detection of epistatic interactions. A QTL analysis of the interspecific wing-size difference revealed QTL with major effects and epistatic interactions among loci affecting the trait. We analyzed 178 hybrid males and initially found two major QTL for wing length, one for wing width, three for a normalized wing-size variable, and five for wing seta density. One QTL for wing width explains 38.1% of the phenotypic variance, and the same QTL explains 22% of the phenotypic variance in normalized wing size. This corresponds to a region previously introgressed from N. giraulti into N. vitripennis that accounts for 44% of the normalized wing-size difference between the species. Significant epistatic interactions were also found that affect wing size and density of setae on the wing. Screening for pairwise epistatic interactions between loci on different linkage groups revealed four additional loci for wing length and four loci for normalized wing size that were not detected in the original QTL analysis. We propose that the evolution of smaller wings in N. vitripennis males is primarily the result of major mutations at few genomic regions and involves epistatic interactions among some loci.

Animals↗

PubMed2003

Change of the heterogametic sex from male to female in the frog.

Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.

Animals↗

PubMed2003

Analysis of natural allelic variation at seed dormancy loci of Arabidopsis thaliana.

Arabidopsis accessions differ largely in their seed dormancy behavior. To understand the genetic basis of this intraspecific variation we analyzed two accessions: the laboratory strain Landsberg erecta (Ler) with low dormancy and the strong-dormancy accession Cape Verde Islands (Cvi). We used a quantitative trait loci (QTL) mapping approach to identify loci affecting the after-ripening requirement measured as the number of days of seed dry storage required to reach 50% germination. Thus, seven QTL were identified and named delay of germination (DOG) 1-7. To confirm and characterize these loci, we developed 12 near-isogenic lines carrying single and double Cvi introgression fragments in a Ler genetic background. The analysis of these lines for germination in water confirmed four QTL (DOG1, DOG2, DOG3, and DOG6) as showing large additive effects in Ler background. In addition, it was found that DOG1 and DOG3 genetically interact, the strong dormancy determined by DOG1-Cvi alleles depending on DOG3-Ler alleles. These genotypes were further characterized for seed dormancy/germination behavior in five other test conditions, including seed coat removal, gibberellins, and an abscisic acid biosynthesis inhibitor. The role of the Ler/Cvi allelic variation in affecting dormancy is discussed in the context of current knowledge of Arabidopsis germination.

Abscisic Acid↗

PubMed2003

Genetic dissection of hybrid incompatibilities between Drosophila simulans and D. mauritiana. I. Differential accumulation of hybrid male sterility effects on the X and autosomes.

The genetic basis of hybrid incompatibility in crosses between Drosophila mauritiana and D. simulans was investigated to gain insight into the evolutionary mechanisms of speciation. In this study, segments of the D. mauritiana third chromosome were introgressed into a D. simulans genetic background and tested as homozygotes for viability, male fertility, and female fertility. The entire third chromosome was covered with partially overlapping segments. Many segments were male sterile, while none were female sterile or lethal, confirming previous reports of the rapid evolution of hybrid male sterility (HMS). A statistical model was developed to quantify the HMS accumulation. In comparison with previous work on the X chromosome, we estimate that the X has approximately 2.5 times the density of HMS factors as the autosomes. We also estimate that the whole genome contains approximately 15 HMS "equivalents"-i.e., 15 times the minimum number of incompatibility factors necessary to cause complete sterility. Although some caveats for the quantitative estimate of a 2.5-fold density difference are described, this study supports the notion that the X chromosome plays a special role in the evolution of reproductive isolation. Possible mechanisms of a "large X" effect include selective fixation of new mutations that are recessive or partially recessive and the evolution of sex-ratio distortion systems.

Animals↗

PubMed2003

A gene block causing cross-incompatibility hidden in wild and cultivated rice.

Unidirectional cross-incompatibility was detected in advanced generations of backcrossing between wild (Oryza rufipogon) and cultivated (O. sativa) rice strains. The near-isogenic line (NIL) of T65wx (Japonica type) carrying an alien segment of chromosome 6 from a wild strain gave a reduced seed setting only when crossed with T65wx as the male. Cytological observations showed that abortion of hybrid seeds occurred as a consequence of a failure of early endosperm development followed by abnormalities in embryo development. The genetic basis of cross-incompatibility reactions in the female and male was investigated by testcrosses using recombinant inbred lines (RILs) that were established through dissecting the introgressed segments of wild and cultivated (Indica type) strains. The results revealed that the cross-incompatibility reaction was controlled by Cif in the female and by cim in the male. When the female plant with Cif was crossed with the male plant with cim, a failure of early endosperm development was observed in the hybrid zygotes. Among cultivars of O. sativa, cim was distributed predominantly in the Japonica type but not in the Indica type. In addition, a dominant suppressor, Su-Cif, which changes the reaction in the female from incompatible to compatible was proposed to present near the centromere of chromosome 6 of the Indica type. Further, the death of young F(1) zygotes was controlled by the parental genotypes rather than by the genotype of the hybrid zygote itself since all three genes acted sporophytically, which strongly suggests an involvement of parent-of-origin effects. We discuss the results in relation to the origin of a crossing barrier as well as their maintenance within the primary gene pool.

Chromosome Mapping↗

PubMed2003

Heterochromatic self-association, a determinant of nuclear organization, does not require sequence homology in Drosophila.

Chromosomes of higher eukaryotes contain blocks of heterochromatin that can associate with each other in the interphase nucleus. A well-studied example of heterochromatic interaction is the brown(Dominant) (bwD) chromosome of D. melanogaster, which contains an approximately 1.6-Mbp insertion of AAGAG repeats near the distal tip of chromosome 2. This insertion causes association of the tip with the centric heterochromatin of chromosome 2 (2h), which contains megabases of AAGAG repeats. Here we describe an example, other than bwD, in which distally translocated heterochromatin associates with centric heterochromatin. Additionally, we show that when a translocation places bwD on a different chromosome, bwD tends to associate with the centric heterochromatin of this chromosome, even when the chromosome contains a small fraction of the sequence homology present elsewhere. To further test the importance of sequence homology in these interactions, we used interspecific mating to introgress the bwD allele from D. melanogaster into D. simulans, which lacks the AAGAG on the autosomes. We find that D. simulans bwD associates with 2h, which lacks the AAGAG sequence, while it does not associate with the AAGAG containing X chromosome heterochromatin. Our results show that intranuclear association of separate heterochromatic blocks does not require that they contain the same sequence.

Animals↗

PubMed2005

A loss of genome buffering capacity of Dahl salt-sensitive model to modulate blood pressure as a cause of hypertension.

Essential hypertension is a complex trait influenced by multiple genes known as quantitative trait loci (QTLs) for blood pressure (BP). It is not clear, however, what roles these QTLs play in maintaining normotension. Insights gained toward the maintenance of normotension will shed light on how hypertension can result from a deficiency or malfunctioning of this maintenance. Currently, congenic strains were systematically constructed using Dahl salt-sensitive (DSS) and Lewis (LEW) rats not only to define QTLs (i.e. in DSS background), but also to ascertain effects of the same QTLs in preserving normotension (i.e. in LEW background), a first such study. Results showed that although LEW alleles for two QTLs on Chromosome (Chr) 18 lowered BP on the DSS background, their BP-increasing DSS alleles failed to influence BP in the LEW background. To further prove that the LEW background is resistant and the DSS background is susceptible to the effects of QTLs, BP-increasing alleles of a QTL on Chr 2 were introgressed into the DSS background, and its BP-decreasing alleles into the LEW background. Indeed, there was no BP-decreasing effect on the LEW background while demonstrating a BP-increasing effect on the DSS background. Thus, a genetic regulation of BP QTLs in the LEW genome inhibits BP changes by nullifying the effects of BP-altering QTLs. In comparison, the DSS genome must have lost the buffering capacity for stabilizing BP. The current work presents good evidence that a lack of regulation for functions of BP QTLs is a potential underlying cause of hypertension.

Animals↗

PubMed2004

The BBZDR/Wor rat model for investigating the complications of type 2 diabetes mellitus.

Congenic and inbred strains of rats offer researchers invaluable insight into the etiopathogenesis of diabetes and associated complications. The inbred Bio-Breeding Zucker diabetic rat (BBZDR)/Wor rat strain is a relatively new and emerging model of type 2 diabetes. This strain was created by classical breeding methods used to introgress the defective leptin receptor gene (Lepr(fa)) from insulin-resistant Zucker fatty rats into the inbred BBDR/Wor strain background. The diabetic male BBZDR/Wor rat is homozygous for the fatty mutation and shares the genetic background of the original BB strain. Although lean littermates are phenotypically normal, obese juvenile BBZDR/Wor rats are hyperlipidemic and hyperleptinemic, become insulin resistant, and ultimately develop hyperglycemia. Furthermore, the BBZDR/Wor rat is immune competent and does not develop autoimmunity. Similar to patients with clinical diabetes, the BBZDR/Wor rat develops complications associated with hyperglycemia. The BBZDR/Wor rat is a model system that fully encompasses the ability to study the complications that affect human type 2 diabetic patients. In this review, recent work that has evaluated type 2 diabetic complications in BBZDR/Wor rats is discussed, including the authors' preliminary unpublished studies on cardiovascular disease.

Animals↗

PubMed1999

BALB/c.CBA/N mice carrying the defective Btk(xid) gene are resistant to pristane-induced plasmacytomagenesis.

The X-chromosome from the CBA/N mouse which carries the defective Bruton's tyrosine kinase (Btk) allele (Xxid) has been introgressively backcrossed onto the plasmacytoma (PCT) induction-susceptible BALB/cAN. Inbred BALB/c.CBA/N-xid/xid (C.CBA/N) mice raised and maintained in our conventional colony were given three 0.5 ml injections of pristane and were highly refractory to PCT induction. Only one PCT was found among 59 mice followed for > or =300 days. Twenty mice were examined at day 200 for foci of plasma cells in the oil granuloma. Ten mice had small foci of plasma cells, most of which were plasmacytotic, embedded in the inflammatory oil granuloma. In one there were multiple foci, but most of the mice had only one or two foci. F1 hybrid XxidY males derived from CBA/N females crossed to BALB/cAnPt were also resistant to PCT induction, while heterozygous and homozygous XY males were susceptible. C.CBA/N mice can develop extensive mucosal plasma cells as well as plasma cell accumulations in oil granuloma tissue, but the precursors of these plasma cells do not give rise to PCT in genetically susceptible hosts. The failure of C.CBA/N mice to develop PCT is probably due to the elimination of B cell clones that can be perpetuated by repeated exposure to thymus-independent type 2 antigens.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed2000

NKT lymphocyte ontogeny and function are impaired in low antibody-producer Biozzi mice: gene mapping in the interval-specific congenic strains raised for immunomodulatory genes.

NKT cells are CD4(+) or CD4(-)CD8(-) CD1d-restricted lymphocytes, characterized by the property to rapidly produce IL-4 and IFN-gamma in response to TCR ligation. This IL-4 burst is lacking in autoimmunity-prone SJL and NOD strains of mice, which suggests an immunoregulatory role for NKT cells. The NKT cell status was thus investigated in the genetically selected high (H) and low (L) antibody-producer mice. The results show that (i) the frequency of cells expressing the NKT cell markers is 3- to 4-fold lower in thymus and spleen from L than H mice, (ii) L mice spleen cells did not produce IL-4 following injection of anti-TCR alpha beta antibody, and (iii) L mice thymus and spleen cells failed to produce IL-4 after in vitro stimulation by anti-TCR alpha beta antibody or alpha-galactosylceramide, a newly described NKT cell ligand. These parameters were investigated in six interval-specific congenic strains raised for the quantitative trait loci which contain the immunomodulatory genes responsible for the high/low antibody production phenotypes. IL-4 production recovery occurred only in the congenic strain in which the H origin chromosome 4 segment was introgressed on the L background. This finding was not due to increased NKT cell frequency but appeared dependent of antigen-presenting cells in co-culture experiments. This result strongly suggests the presence of gene(s) modulating NKT function on chromosome 4, close to several genes predisposing to autoimmunity.

Animals↗