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201.
Dominance Is the Major Genetic Basis of Heterosis in Rice as Revealed by Qtl Analysis Using Molecular Markers 总被引:39,自引:1,他引:38
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A set of 194 F(7) lines derived from a subspecific rice cross showing strong F(1) heterosis was backcrossed to the two parents. The materials (388 BC(1)F(7) lines, 194 F(8) lines, two parents, F(1)) were phenotyped for 12 quantitative traits. A total of 37 significant QTLs (LOD >/= 2.0) was detected through 141 RFLP markers in the BC(1)F(7) populations. Twenty-seven (73%) quantitative trait loci (QTLs) were detected in only one of the BC(1)F(7) populations. In 82% of these cases, the heterozygotes were superior to the respective homozygotes. The remaining 10 (27%) QTLs were detected in both BC(1)F(7) populations, and the heterozygote had a phenotype falling between those of the two homozygotes and in no instances were the heterozygotes found to be superior to both homozygotes. These results suggest that dominance complementation is the major genetic basis of heterosis in rice. This conclusion was strengthened by the finding that there was no correlation between most traits and overall genome heterozygosity and that there were some recombinant inbred lines in the F(8) population having phenotypic values superior to the F(1) for all of the traits evaluated--a result not expected if overdominance was a major contributor to heterosis. Digenic epistasis was not evident. 相似文献
202.
Pollen grains were harvested from an interspecific F1 hybrid between the cultivated tomato, Lycopersicon esculentum Mill., and its wild relative Lycopersicon hirsutum Humb. & Bonpl., a low temperature tolerant accession originating from an altitude of 3200 m in the Peruvian Andes. The two species differ for electrophoretically-detectable loci that mark six (possibly seven) of the 12 tomato chromosomes. Isozyme analysis of the BC1 populations derived from controlled pollinations at normal and low temperatures indicates a significant skewing of allelic frequencies favoring two independent chromosome segments of L. hirsutum at low temperatures. The results demonstrate that gametophytic selection for low temperature tolerance of tomato pollen is determined, at least in part, by genes expressed in the haploid pollen. 相似文献
203.
Dr. D. Tanksley Dr. H. Medina-Filho C. M. Rick 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1981,60(5):291-296
Summary The extent of correlation was estimated between isozyme genotypes and the four widely segregating characters — leaf segment W/L ratio, stigma exsertion, fruit weight, and seed weight — in the first backcross of F1
Lycopersicon esculentum x Solanum pennellii to the former parent. The inbred parents differ in their alleles at the 12 tested isozymic loci, which are known to mark a minimum of eight of the twelve tomato chromosomes. Based on the isozyme data, a mean heterozygosity value, ¯H, was calculated which estimates the proportion of pennillii alleles in each individual. Correlations between mean heterozygosity and observed levels of each quantitative trait were highly significant and positive or negative as expected from the relative parental values. Plants with the lowest mean heterozygosity — i.e., closest to the esculentum zymotype also had mean values closest to those of this parent amongst the whole backcross population for each of the quantitative traits.Bivariate and multiple regression analysis was used to evaluate the ability of isozymes vs diagnostic morphological characters to estimate the portion of recurrent parent genes carried in each backcross individual. The results suggest that isozyme data gives better estimates than single diagnostic morphological characters and approach the level obtained by combinations of three morphological traits. Since electrophoretic determinations are made on small seedlings, selection at that stage can effect great savings of space and effort by greatly deminishing the size of the population needed at maturity. As such, isozyme selection would precede morphological selection but not replace it, thus the predictive value of these biochemical markers as well as diagnostic morphological characters could be obtained. 相似文献
204.
Charles M. Rick Jon F. Fobes Steven D. Tanksley 《Plant Systematics and Evolution》1979,132(4):279-298
Populations in the central part of the distribution are mostly self-incompatible and tend to be highly variable for allozymic and morphological characters; those in the north and south limits are entirely self-compatible and tend to be genetically highly uniform. Gradations in variability are observed in the intermediate regions. Flower size tends to diminish in the peripheral areas. The extensive differences in genotype observed between the north and south marginal populations are not compatible with the concept of a single origin of self-compatibility, but suggest, along with other evidence, that the substitution of different alleles resulted from differentiation in the marginal areas from older, self-incompatible stocks of the central region. The conclusions regarding patterns of genetic variation and nature of evolution of mating systems inL. hirsutum conform to a remarkable extent with those reached previously forL. pimpinellifolium, a species that is distinct in morphology and ecological preferences yet has a similar latitudinal distribution. 相似文献
205.
D. Bernacchi T. Beck-Bunn D. Emmatty Y. Eshed S. Inai J. Lopez V. Petiard H. Sayama J. Uhlig D. Zamir S. Tanksley 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(7):1191-1196
Improved-processing tomato lines were produced by the molecular breeding strategy of advanced backcross QTL (AB-QTL) analysis.
These near-isogenic lines (NILs) contained unique introgressions of wild alleles originating from two donor wild species,
Lycopersicon hirsutum (LA1777) and L. pimpinellifolium (LA1589). Wild alleles targeted for trait improvement were selected on the basis of previously published replicated QTL data
obtained from advanced backcross populations for a battery of important agronomic traits. Twenty three NILs were developed
for 15 genomic regions which were predicted to contain 25 quantitative trait factors for the improvement of seven agronomic
traits: total yield, red yield, soluble solids, brix×red yield, viscosity, fruit color, and fruit firmness. An evaluation
of the agronomic performance of the NILs in five locations worldwide revealed that 22 out of the 25 (88%) quantitative factors
showed the phenotypic improvement predicted by QTL analysis of the BC3 populations, as NILs in at least one location. Per-location gains over the elite control ranged from 9% to 59% for brix×red
yield; 14% to 33% for fruit color; 17% to 34% for fruit firmness; 6% to 22% for soluble-solids content; 7% to 22% for viscosity;
15% to 48% for red yield, and 20% to 28% for total yield. The inheritance of QTLs, the implementation of the AB-QTL methodology
for characterizing unadapted germplasm and the applicability of this method to other crops are discussed.
Theor Appl Genet (1998) 97 : 170–180
Received: 27 October 1997 / Accepted: 25 November 1997 相似文献
206.
A tomato lambda genomic library was screened with the human minisatellites 33.6 and 33.15. Similar tomato sequences are estimated to occur on average every 4000 kb. In thirteen hybridizing clones characterized, the size of minisatellite arrays varied between 100 bp and 3 kb. The structure of the repetitive elements is complex as the human core sequence is interspersed with other elements. In three cases, sequences similar to the human minisatellites were part of a higher-order tandem repeat. The chromosomal position of these sequences was established by ascertaining linkage to previously mapped RFLP markers. In contrast to the human genome, no clustering of minisatellite loci was observed in tomato. The fingerprints generated by hybridizing tomato minisatellites to genomic DNA of a set of cultivars were, in two cases, more variable than those obtained with 33.6 or 33.15. Two of the characterized probes detected 4–8 alleles of a single locus, which displayed 10–15 times more polymorphism than random RFLP clones. Some minisatellites contain di- and tri-nucleotide microsatellite repeated motifs which may account for the high level of polymorphism detected with these clones. 相似文献
207.
Marion S. Röder Nora L. V. Lapitan Mark E. Sorrells Steven D. Tanksley 《Molecular & general genetics : MGG》1993,238(1-2):294-303
Barley (Hordeum vulgare L.) telomeres were investigated by means of pulsed field gel electrophoresis (PFGE) and in situ hybridization. In situ hybridization showed that a tandemly repeated satellite sequence has a subtelomeric location, and is present at thirteen of the fourteen chromosome ends. PFGE revealed that this satellite sequence is physically close to the telomeric repeat. Pulsed field gel electrophoresis was then used for segregation analysis and linkage mapping of several telomeric and satellite loci in a segregating doubled-haploid population. The telomeric repeat displayed a hypervariable segregation pattern with new alleles occurring in the progeny. Eight satellite and telomeric sites were mapped on an restriction fragment length polymorphism (RFLP)-map of barley, defining the ends of chromosome arms 1L, 2S, 3L, 4S, 4L, 5S and 6. One satellite locus mapped to an interstitial site on the long arm of chromosome 3. The pyhsical location of this locus was confirmed by in situ hybridization to wheat/barley addition line 3. 相似文献
208.
Rod A. Wing Hong-Bin Zhang Steven D. Tanksley 《Molecular genetics and genomics : MGG》1994,242(6):681-688
A map-based cloning scheme is being used to isolate the jointless (j) gene of tomato. The jointless locus is defined by a single recessive mutation that completely suppresses the formation of the fruit and flower pedicel and peduncle abscission zone. jointless was mapped in an F2 population of an interspecific cross between Lycopersicon esculentum and Lycopersicon pennellii to a 7.1 cM interval between two restriction fragment length polymorphism (RFLP) markers TG523 and TG194. Isogenic DNA pools were then constructed from a subset of the mapping population and screened with 800 random decamers for random amplification of polymorphic DNA (RAPD) polymorphisms. Five new RAPD markers were isolated and mapped to chromosome 11, two of which were mapped within the targeted interval. One marker, RPD158, was mapped 1.5 cM to the opposite side of jointless relative to TG523 and thus narrowed the interval between the closest flanking markers to 3.0 cM. Physical mapping by pulse-field gel electrophoresis using TG523 and RPD158 as probes demonstrated that both markers hybridize to a common 600 kb SmaI restriction fragment. This provided an estimate of 200 kb/cM for the relationship between physical and genetic distances in the region of chromosome 11 containing the j locus. The combined results provide evidence for the feasibility of the next step toward isolation of the jointless gene by map-based cloning — a chromosome walk or jump to jointless. 相似文献
209.
Restriction fragment length polymorphism maps and the concept of graphical genotypes 总被引:27,自引:0,他引:27
N. D. Young S. D. Tanksley 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(1):95-101
Summary With the advent of high density restriction fragment length polymorphism (RFLP) maps, it has become possible to determine the genotype of an individual at many genetic loci simultaneously. Often, such RFLP data are expressed as long strings of numbers or letters indicating the genotype for each locus analyzed. In this form, RFLP data can be difficult to interpret or utilize without complex statistical analysis. By contrast, numerical genotype data can also be expressed in a more useful, graphical form, known as a graphical genotype, which is described in detail in this paper. Ideally, a graphical genotype portrays the parental origin and allelic composition throughout the entire genome, yet is simple to comprehend and utilize. In order to demonstrate the usefulness of this concept, graphical genotypes for individuals from backcross and F2 populations in tomato are described. The concept can also be utilized in more complex mating schemes involving two or more parents. A model that predicts the accuracy of graphical genotypes is presented for hypothetical RFLP maps of varying marker spacing. This model indicates that graphical genotypes can be more than 99% correct in describing a genome of total size, 1000 cM, with RFLP markers located every 10 cM. In order to facilitate the application of graphical genotypes to genetics and breeding, we have developed computer software that generates and manipulates graphical genotypes. The concept of graphical genotypes should be useful in whole genome selection for polygenic traits in plant and animal breeding programs and in the diagnosis of heterogenously based genetic diseases in humans. 相似文献
210.
RFLP analysis of the size of chromosomal segments retained around the Tm-2 locus of tomato during backcross breeding 总被引:3,自引:0,他引:3
N. D. Young S. D. Tanksley 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(3):353-359
Summary Genes introduced into cultivated plants by backcross breeding programs are flanked by introgressed segments of DNA derived from the donor parent. This phenomenon is known as linkage drag and is frequently thought to affect traits other than the one originally targeted. The Tm-2 gene of Lycopersicon peruvianum, which confers resistance to tobacco mosaic virus, was introduced into several different tomato cultivars (L. esculentum) by repeated backcrossing. We have measured the sizes of the introgressed segments flanking the Tm-2 locus in several of these cultivars using a high density map of restriction fragment length polymorphic (RFLP) markers. The smallest introgressed segment is estimated to be 4 cM in length, while the longest is over 51 cM in length and contains the entire short arm of chromosome 9. Additionally, RFLP analysis was performed on remnant seed from different intermediate generations corresponding to two different backcross breeding programs for TMV resistance. The results reveal that plants containing desirable recombination near the resistance gene were rarely selected during backcrossing and, as a result, the backcross breeding method was largely ineffective in reducing the size of linked DNA around the resistance gene. We propose that, by monitoring recombination around genes of interest with linked RFLP markers, one can quickly and efficiently reduce the amount of linkage drag associated with introgression. Using such a procedure, it is estimated that an introgressed segment can be obtained in two generations that is as small as that which would otherwise require 100 backcross generations without RFLP selection. 相似文献