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Showing papers in "Theoretical and Applied Genetics in 1992"


Journal ArticleDOI
TL;DR: Many of the factors that affected plant height quantitatively in this investigation were found to map to regions also including known sites of major genes influencing plant height, suggesting that some of the identified QTLs may be allelic to known major genes affecting plant height.
Abstract: Restriction fragment length polymorphisms have become powerful tools for genetic investigations in plant species. They allow a much greater degree of genome saturation with neutral markers than has been possible with isozymes or morphological loci. A previous investigation employed isozymes as genetic markers to infer the location of genetic factors influencing the expression of quantitative traits in the maize population: (CO159×Tx303)F2. This investigation was conducted to examine the inferences that might be derived using a highly saturated map of RFLP markers and isozymes to detect quantitative trait loci (QTLs) in the same maize F2 population. Marker loci that were associated with QTL effects in this investigation generally corresponded well with previous information where such comparisons were possible. Additionally, a number of previously unmarked genomic regions were found to contain factors with large effects on some plant traits. Availability of numerous marker loci in some genomic regions allowed: more accurate localization of QTLs, resolution of linkage between QTLs affecting the same traits, and determination that some chromsome regions previously found to affect a number of traits are likely to be due to linkage of QTLs affecting different traits. Many of the factors that affected plant height quantitatively in this investigation were found to map to regions also including known sites of major genes influencing plant height. Although the data are not conclusive, they suggest that some of the identified QTLs may be allelic to known major genes affecting plant height.

468 citations


Journal ArticleDOI
TL;DR: The accuracy of a promising method that employs pairs of neighbouring markers to obtain maximum linkage information about the presence of a QTL within the enclosed chromosomal segment was investigated by computer simulation and showed that there is a reasonable probability of detecting QTLs that explain at least 5% of the total variance.
Abstract: The development of linkage maps with large numbers of molecular markers has stimulated the search for methods to map genes involved in quantitative traits (QTLs). A promising method, proposed by Lander and Botstein (1989), employs pairs of neighbouring markers to obtain maximum linkage information about the presence of a QTL within the enclosed chromosomal segment. In this paper the accuracy of this method was investigated by computer simulation. The results show that there is a reasonable probability of detecting QTLs that explain at least 5% of the total variance. For this purpose a minimum population of 200 backcross or F2 individuals is necessary. Both the number of individuals and the relative size of the genotypic effect of the QTL are important factors determining the mapping precision. On the average, a QTL with 5% or 10% explained variance is mapped on an interval of 40 or 20 centiMorgans, respectively. Of course, QTLs with a larger genotypic effect will be located more precisely. It must be noted, however, that the interval length is rather variable.

455 citations


Journal ArticleDOI
TL;DR: In wheat, the non-homoeologous, non-dose responsive and dominant behaviour of RAPD products devalues their use as genetic markers for the construction of linkage maps, and the high probability that the amplified fragments derive from repetitive DNA limits theirUse as a source of conventional RFLP probes.
Abstract: An evaluation was made of the use of random amplified polymorphic DNA (RAPD) as a genetic marker system in wheat. Reproducible amplification products were obtained from varietal, homozygous single chromosome recombinant line and wheat/alien addition line genomic DNA with selected primers and rigorously optimized reaction conditions. Factors influencing the RAPD patterns are DNA concentration, Mg2+ concentration, polymerase concentration and denaturing temperature. In wheat, the non-homoeologous, non-dose responsive and dominant behaviour of RAPD products devalues their use as genetic markers for the construction of linkage maps, and the high probability that the amplified fragments derive from repetitive DNA limits their use as a source of conventional RFLP probes. However, RAPD markers will most certainly find many applications in the analysis of genotypes where single chromosomes or chromosome segments are to be manipulated.

451 citations


Journal ArticleDOI
TL;DR: It is shown that the observed difference in quantitative trait values associated with alternative marker genotypes in the selected population can be much greater than the actual gene effect at the quantitative trait locus when the entire population is considered.
Abstract: "Selective genotyping" is the term used when the determination of linkage between marker loci and quantitative trait loci (QTL) affecting some particular trait is carried out by genotyping only individuals from the high and low phenotypic tails of the entire sample population Selective genotyping can markedly decrease the number of individuals genotyped for a given power at the expense of an increase in the number of individuals phenotyped The optimum proportion of individuals genotyped from the point of view of minimizing costs for a given experimental power depends strongly on the cost of completely genotyping an individual for all of the markers included in the experiment (including the costs of obtaining a DNA sample) relative to the cost of rearing and trait evaluation of an individual However, in single trait studies, it will almost never be useful to genotype more than the upper and lower 25% of a population It is shown that the observed difference in quantitative trait values associated with alternative marker genotypes in the selected population can be much greater than the actual gene effect at the quantitative trait locus when the entire population is considered An expression and a figure is provided for converting observed differences under selective genotyping to actual gene effects

400 citations


Journal ArticleDOI
TL;DR: Regression models that use information obtained from three or more nearby markers are shown to be useful in separating the effects of QTLs in neighbouring regions.
Abstract: The use of information from flanking markers to estimate the position and size of the effect of a quantitative trait locus (QTL) lying between two markers is shown to be affected by QTLs lying in neighbouring regions of the chromosome. In some situations the effects of two QTLs lying outside the flanked region are reinforced in such a way that a ‘ghost’ QTL may be mistakenly identified as a real QTL. These problems are discussed in the framework of a backcross using a regression model as the analytical tool to present the theoretical results. Regression models that use information obtained from three or more nearby markers are shown to be useful in separating the effects of QTLs in neighbouring regions. A simulated data set exemplifies the problem and is analysed by the interval mapping method as well as by the regression model.

370 citations


Journal ArticleDOI
TL;DR: An analysis of problems and a general method for mapping polyploids based on segregation of single-dose restriction fragments (SDRFS) are presented and it is estimated that a population size of 75 is required to identify SDRFs with 98% level of confidence for the four ploidy levels.
Abstract: Restriction fragment length polymorphism (RFLP) linkage maps have been constructed in several major diploid crops. However, construction of RFLP maps directly in polyploids has lagged behind for several reasons: (1) there are a large number of possible genotypes for each DNA probe expected in a segregating population, and these genotypes cannot always be identified readily by their banding phenotypes; and (2) the genome constitutions (allopolyploidy versus autopolyploidy) in many high polyploids are not clearly understood. We present here an analysis of these problems and propose a general method for mapping polyploids based on segregation of single-dose restriction fragments (SDRFS). SDRFs segregate 1:1 (presence: absence) in gametes of heterozygous plants. Hypothetical allopolyploid and autopolyploid species with four ploidy levels of 2n = 4x, 6x, 8x, and 10x, are used to illustrate the procedures for identifying SDRFs, detecting linkages among SDRFs, and distinguishing allopolyploid versus autopolyploids from polyploids of unknown genome constitution. Family size required, probability of linkage, and attributes of different mapping populations are discussed. We estimate that a population size of 75 is required to identify SDRFs with 98% level of confidence for the four ploidy levels. This population size is also adequate for detecting and estimating linkages in the coupling phase for both allopolyploids and autopolyploids, but linkages in the repulsion phase can be estimated only in allopolyploids. For autopolyploids, it is impractical to estimate meaningful linkages in repulsion because very large family sizes (>750) are required. For high-level polyploids of unknown genome constitution, the ratio between the number of detected repulsion versus coupling linkages may provide a crude measurement of preferential chromosome pairing, which can be used to distinguish allopolyploidy from autopolyploidy. To create a mapping population, one parent (P1) should have high heterozygosity to ensure a high frequency of SDRFs, and the second parent (P2) should have a low level of heterozygosity to increase the probability of detecting polymorphic fragments. This condition could be satisfied by choosing outcrossed hybrids as one parental type and inbreds, haploids, or doubled haploids as the other parental type.

365 citations


Journal ArticleDOI
TL;DR: Results from these analyses suggest that BBCC tetraploids (O. malampuzhaensis, O. punctata and O. minuta) are either of independent origins or have experienced introgression from sympatric C-genome diploid rice species.
Abstract: Ninety-three accessions representing 21 species from the genus Oryza were examined for restriction fragment length polymorphism. The majority (78%) of the accessions, for which five individuals were tested, were found to be monomorphic. Most of the polymorphic accessions segregated for only one or two probes and appeared to be mixed pure lines. For most of the Oryza species tested, the majority of the genetic variation (83%) was found between accessions from different species with only 17% between accessions within species. Tetraploid species were found to have, on average, nearly 50% more alleles (unique fragments) per individual than diploid species reflecting the allopolyploid nature of their genomes.

334 citations


Journal ArticleDOI
TL;DR: An expanded soybean RFLP map and quantitative trait loci (QTL) in soybean [Glycine max (L.) Merr.] for seed protein and oil content were presented and G. soja alleles at significant loci for protein content were associated with greater protein content than G. max alleles.
Abstract: The objectives of this study were to present an expanded soybean RFLP map and to identify quantitative trait loci (QTL) in soybean [Glycine max (L.) Merr.] for seed protein and oil content. The study population was formed from a cross between a G. max experimental line (A81-356022) and a G. soja Sieb. and Zucc. plant introduction (PI 468916). A total of 252 markers was mapped in the population, forming 31 linkage groups. Protein and oil content were measured on seed harvested from a replicated trial of 60 F2-derived lines in the F3 generation (F2∶3 lines). Each F2∶3 line was genotyped with 243 RFLP, five isozyme, one storage protein, and three morphological markers. Significant (P<0.01) associations were found between the segregation of markers and seed protein and oil content. Segregation of individual markers explained up to 43% of the total variation for specific traits. All G. max alleles at significant loci for oil content were associated with greater oil content than G. soja alleles. All G. soja alleles at significant loci for protein content were associated with greater protein content than G. max alleles.

309 citations


Journal ArticleDOI
TL;DR: Two genomic libraries were established to provide markers to develop an integrated map combining molecular markers and genes for qualitative and quantitative morpho-agronomic traits in common bean, and a positive correlation was observed between the average size of hybridizing restriction fragments and the frequency of polymorphism detected by each restriction enzyme.
Abstract: Two genomic libraries were established to provide markers to develop an integrated map combining molecular markers and genes for qualitative and quantitative morpho-agronomic traits in common bean. Contrasting characteristics were observed for the two libraries. While 89% of the PstI clones were classified as single-copy sequences, only 21% of the EcoRIBamHI clones belonged in that category. Clones of these two libraries were hybridized against genomic DNA of nine genotypes chosen according to their divergent evolutionary origin and contrasting agronomic traits. Eight restriction enzymes were used in this study. PstI clones revealed 80–90% polymorphism between the Andean and Middle American gene pools and 50–60% polymorphism within these gene pools. However, under the same conditions only 30% of the EcoRI-BamHI clones showed polymorphism between the Middle American and Andean gene pools. Hybridization with PstI clones to EcoRI-, EcoRV-, or HindIII-digested genomic DNA resulted in a cumulative frequency of polymorphism of approximately 80%. Hybridizations to BamHI-, HaeIII-, HinfI-, PstI-, and XbaI-digested genomic DNA detected no additional polymorphisms not revealed by the former three enzymes. In the PstI library, a positive correlation was observed between the average size of hybridizing restriction fragments and the frequency of polymorphism detected by each restriction enzyme. This relationship is consistent with the higher proportion of insertion/deletion events compared with the frequency of nucleotide substitutions observed in that library.

284 citations


Journal ArticleDOI
TL;DR: Investigation of RAPDs using Brassica, Sinapis and Raphanus taxa revealed the classical U triangle relationship between diploid and amphidiploid Brassica taxa and suggested at least ten primers are needed to adequately portray these relationships.
Abstract: The potential use of RAPDs for taxonomic studies were investigated using Brassica, Sinapis and Raphanus taxa. Principal coordinate analysis of 284 RAPD bands revealed the classical U triangle relationship between diploid and amphidiploid Brassica taxa. Raphanus sativus and S. alba were distinct from the Brassica taxa. It appears that at least ten primers with approximately 100 total bands are needed to adequately portray these relationships. Cultivars of cabbage and cauliflower were separated by RAPDs. Analysis of RAPDs from individual plants of B. carinata cv. dodola resulted in 69 RAPDs, with 91.7% monomorphic and 8.3% polymorphic bands. RAPDs appear to be useful for taxonomic studies at levels ranging from populations to species and perhaps genera.

269 citations


Journal ArticleDOI
TL;DR: The genomic in-situ hybridization method is fast, sensitive, accurate and informative and likely to be of great value for both cytogenetic analysis and in plant breeding programmes.
Abstract: Genomic in situ hybridization was used to identify alien chromatin in chromosome spreads of wheat, Triticum aestivum L., lines incorporating chromosomes from Leymus multicaulis (Kar. and Kir.) Tzvelev and Thinopyrum bessarabicum (Savul. and Rayss) Love, and chromosome arms from Hordeum chilense Roem. and Schult, H. vulgare L. and Secale cereale L. Total genomic DNA from the introgressed alien species was used as a probe, together with excess amounts of unlabelled blocking DNA from wheat, for DNA:DNA in-situ hybridization. The method labelled the alien chromatin yellow-green, while the wheat chromosomes showed only the orange-red fluorescence of the DNA counterstain. Nuclei were screened from seedling root-tips (including those from half-grains) and anther wall tissue. The genomic probing method identified alien chromosomes and chromosome arms and allowed counting in nuclei at all stages of the cell cycle, so complete metaphases were not needed. At prophase or interphase, two labelled domains were visible in most nuclei from disomic lines, while only one labelled domain was visible in monosomic lines. At metaphase, direct visualization of the morphology of the alien chromosome or chromosome segment was possible and allowed identification of the relationship of the alien chromatin to the wheat chromosomes. The genomic in-situ hybridization method is fast, sensitive, accurate and informative. Hence it is likely to be of great value for both cytogenetic analysis and in plant breeding programmes.

Journal ArticleDOI
TL;DR: Analysis of the 49 loci mapped showed extreme clustering around the centromere in all four maps, with large ‘gaps’ in the distal chromosome regions, which is interpreted as being due to strong localisation of recombination towards the ends of the wheat and rye chromosomes.
Abstract: Genetic maps of chromosomes 3A, 3B and 3D of wheat and 3R of rye were developed using 22 DNA probes and two isozyme marker systems. Analysis of the 49 loci mapped showed extreme clustering around the centromere in all four maps, with large 'gaps' in the distal chromosome regions, which is interpreted as being due to strong localisation of recombination towards the ends of the wheat and rye chromosomes. In the centromeric regions gene orders are highly conserved between the three wheat genomes and the rye genome. However, the unpredictable behaviour of the DNA clones that map in distal chromosome locations may indicate that the genomes are diverging most rapidly in the regions of higher recombination. A comparison of cDNA and genomic probes showed the latter to be much more efficient for revealing RFLP. Some classes of gDNA clones, i.e. chromosome-specific sequences and those hybridizing in a non-homoeologous manner, were seen to be most polymorphic. Correlations between map locations and RFLP levels showed no clear relationship. In addition to anonymous DNA clones, the locations of known function clones, sedoheptulose-1,7-bisphosphatase (XSbp), carboxypeptidase I (XCxp1) and a bZIP protein (XEmbp), were ascertained along with those for two isozyme loci, Mal-1 and Est-5.

Journal ArticleDOI
TL;DR: It was deduced that the processes leading to differentiation involved a combination of molecular events that include base substitutions and insertion/deletions, which demonstrate that indica rice is genetically more diverse than japonica type.
Abstract: Genetic diversity and differentiation in indica and japonica groups of the cultivated rice (Oryza sativa L.) were studied by assaying DNA restriction fragment length polymorphisms of 12 indica and 14 japonica rice lines digested with three restriction endonucleases. A total of 49 probes were selected to represent the entire RFLP map at intervals of 20-30 cM. It was shown that 95 of the 145 possible probe/enzyme combinations, involving 43 probes and all three enzymes, detected restriction fragment length variation, and the degree of polymorphism varied greatly from one probe/enzyme combination to another. These results demonstrate that indica rice is genetically more diverse than japonica type. Significant differentiation between the two rice groups was detected by 33 probes representing 11 of the 12 rice chromosomes. It was deduced that the processes leading to differentiation involved a combination of molecular events that include base substitutions and insertion/deletions.

Journal ArticleDOI
TL;DR: Quantitative analyses of total protein extracts from 22 cultivars of bread wheat showed that the presence of either subunit 1Ax1 or 1Ax2*, when compared with a null allele, resulted in an increase in the proportion of HMW subunit protein from ca.
Abstract: A gene encoding the high-molecular-weight (HMW) subunit of glutenin 1Ax1 was isolated from bread wheat cv Hope. Comparison of the deduced amino acid sequence with that previously reported for an allelic subunit, 1Ax2*, showed only minor differences, which were consistent with both subunits being associated with good bread-making quality. Quantitative analyses of total protein extracts from 22 cultivars of bread wheat showed that the presence of either subunit 1Ax1 or 1Ax2*, when compared with a null allele, resulted in an increase in the proportion of HMW subunit protein from ca. 8 to 10% of the total. It is suggested that this quantitative increase in HMW subunit protein may account for the association of 1Ax subunits with good quality.

Journal ArticleDOI
TL;DR: Backcross progeny produced from interspecific hybrids of O. sativa cv ‘IR31917-45-3-2’ and O. minuta Acc.
Abstract: Oryza minuta J. S. Presl ex C. B. Presl is a tetraploid wild rice with resistance to several insects and diseases, including blast (caused by Pyricularia grisea) and bacterial blight (caused by Xanthomonas oryzae pv. oryzae). To transfer resistance from the wild species into the genome of cultivated rice (Oryza sativa L.), backcross progeny (BC1, BC2, and BC3) were produced from interspecific hybrids of O. sativa cv 'IR31917-45-3-2' (2n=24, AA genome) and O. minuta Acc. 101141 (2n=48, BBCC genomes) by backcrossing to the O. sativa parent followed by embryo rescue. The chromosome numbers ranged from 44 to 47 in the BC1 progeny and from 24 to 37 in the BC2 progeny. All F1 hybrids were resistant to both blast and bacterial blight. One BC1 plant was moderately susceptible to blast while the rest were resistant. Thirteen of the 16 BC2 progeny tested were resistant to blast; 1 blast-resistant BC2, plant 75-1, had 24 chromosomes. A 3 resistant: 1 susceptible segregation ratio, consistent with the action of a major, dominant gene, was observed in the BC2F2 and BC2F3 generations. Five of the BC1 plants tested were resistant to bacterial blight. Ten of the 21 BC2 progeny tested were resistant to Philippine races 2, 3, and 6 of the bacterial blight pathogen. One resistant BC2, plant 78-1, had 24 chromosomes. The segregation of reactions of the BC2F2, BC2F3, and BC2F4 progenies of plant 78-1 suggested that the same or closely linked gene(s) conferred resistance to races 2, 3, 5, and 6 of the bacterial blight pathogen from the Philippines.

Journal ArticleDOI
TL;DR: The development of this chromosomal arm map for common wheat is viewed as a complement to, rather than as a substitute for, a conventional RFLP linkage map in wheat.
Abstract: A chromosomal arm map has been developed for common wheat (Triticum aestivum L. em. Thell.) using aneuploid stocks to locate more than 800 restriction fragments corresponding to 210 low-copy DNA clones from barley cDNA, oat cDNA, and wheat genomic libraries. The number of restriction fragments per chromosome arm correlates moderately well with relative DNA content and length of somatic chromosomes. The chromosomal arm locations of loci detected with 6 different clones support an earlier hypothesis for the occurrence of a two-step translocation (4AL to 5AL, 5AL to 7BS, and 7BS to 4AL) in the ancestral wheat genomes. In addition, 1 clone revealed the presence of a 5AL segment translocated to 4AL. Anomalies in aneuploid stocks were also observed and can be explained by intrahomoeologous recombination and polymorphisms among the stocks. We view the development of this chromosomal arm map as a complement to, rather than as a substitute for, a conventional RFLP linkage map in wheat.

Journal ArticleDOI
TL;DR: The genealogy of chromosomes sharing duplicated segments was formulated and indicates that B. oleracea is a secondary polyploid species derived from ancestral genome(s) of fewer chromosomes.
Abstract: A composite linkage map of Brassica oleracea was developed from maps of four different populations, derived from 108 DNA, isozyme and morphological loci covering over 747 centimorgans in 11 linkage groups. Of these linkage groups, 8 were assigned to their respective chromosomes by alignment with gene synteny groups of B. oleracea. Distortions in segregation ratios increased with the level of divergence of the parents and were attributed to differentiation of parental chromosomes. Comparison of the individual maps demonstrates that the B. oleracea genome undergoes frequent chromosomal rearrangement, even at the subspecies level. Small inversions were the most frequent form of aberration followed by translocations. The former type of aberration could occur without a noticeable effect on meiotic behavior of chromosomes or on pollen fertility. The obvious deduction from the composite map is that a large fraction of the B. oleracea genome is duplicated, falling into three classes: randomly dispersed, linked-gene families, and blocks duplicated in non-homologous chromosomes. The genealogy of chromosomes sharing duplicated segments was formulated and indicates that B. oleracea is a secondary polyploid species derived from ancestral genome(s) of fewer chromosomes.

Journal ArticleDOI
TL;DR: Genetic maps of wheat chromosome 4A and rye chromosome arm 5RL, and the chromosomal locations of 70 sets of isozyme and molecular homoeoloci have been used to further define the structure of wheat chromosomes 4A, 5A and 7B, and rye chromosomes 4R, 5R and 7R are used.
Abstract: Genetic maps of wheat chromosome 4A and rye chromosome arm 5RL, and the chromosomal locations of 70 sets of isozyme and molecular homoeoloci have been used to further define the structure of wheat chromosomes 4A, 5A and 7B, and rye chromosomes 4R, 5R and 7R. We provide evidence, for the first time, which is consistent with the presence of an interstitial segment on 4AL originating from 5AL, and of a segment originally from 5RL on 7RS. The evolutionary origins of the present chromosomes are discussed.

Journal ArticleDOI
TL;DR: It is demonstrated that RAPD markers can be of great value in gene bank management for purposes of identification, measurement of variation, and establishment of genetic similarity at the intraspecific level.
Abstract: Effective conservation and the use of plant genetic resources are essential for future agricultural progress. Critical to this conservation effort is the development of genetic markers which not only distinguish individuals and accessions but also reflect the inherent variation and genetic relationships among collection holdings. We have examined the applicability of the random amplified polymorphic DNA (RAPD) assay for quick, cost-effective, and reliable use in addressing these needs in relation to collection organization and management. Twenty-five decamer oligonucleotide primers were screened individually with a test array composed of individuals representing a range of genetic relationships in Brassica oleracea L. (vegetable and forage cole crops). Over 140 reproducible, polymorphic fragments were generated for study. Each individual of the test array exhibited a unique molecular genotype and composites specific for accessions and botanical varieties could be established. An analysis of similarity based on amplified DNA fragments reflected the known genetic relationships among the selected entries. These results demonstrated that RAPD markers can be of great value in gene bank management for purposes of identification, measurement of variation, and establishment of genetic similarity at the intraspecific level.

Journal ArticleDOI
TL;DR: The contribution of introgressed regions derived from wild species to the genetic variation within the species of Lycopersicon esculentum was investigated by comparing the RFLP patterns of 2 introgression-free, obsolete cultivars and a modern cultivar that carries at least 5 introgressive resistance genes.
Abstract: The contribution of introgressed regions derived from wild species to the genetic variation within the species of Lycopersicon esculentum was investigated by comparing the RFLP patterns of 2 introgression-free, obsolete cultivars ('Moneymaker' and 'Premier') and a modern cultivar ('Sonatine') that carries at least 5 introgressed resistance genes. In this analysis 195 mapped nuclear markers were used in combination with 6 restriction enzymes. Among the 1170 probe-enzyme combinations tested, only 3 showed a polymorphism between the 2 introgression-free cultivars. On the other hand 24 probe-enzyme combinations were found to exhibit polymorphisms between 'Moneymaker' and 'Sonatine'. These represented ten polymorphic loci distributed among 5 linkage groups on chromosomes 1, 3, 4, 6, and 9.On the assumption that most of the polymorphic loci corresponded to introgressed chromosome segments of wild species carrying resistance genes, linkages between these loci and the component resistance genes were examined by RFLP analysis of pairs of near-isogenic lines differing only for one particular resistance gene, and a variety of commercial cultivars having different resistance gene compositions. Two of the polymorphic linkage groups could thus be ascribed to resistance genes whose map positions were already known: Cf2 on chromosome 6 and Tm2a on chromosome 9, whereas another marker, TG301 on chromosome 1, could be assigned to the Cladosporium fulvum resistance gene Cf9 with a hitherto disputable map position. By linkage analysis of a segregating F2 population the genetic distance between the Cf9 gene and the marker TG301 was estimated at 5.5 ± 2.3 cM.

Journal ArticleDOI
Rex Bernardo1
TL;DR: Computer simulation was used to investigate a more complex but more realistic genetic model involving incomplete coverage of QTL by molecular markers, and found dominance effects are strong and trait heritability is high.
Abstract: In studies involving isozymes or restriction fragment length polymorphisms (RFLPs), correlations of parental molecular marker diversity with grain yield of maize (Zea mays L.) single-crosses have been too low to be of any predictive value. The relationship of molecular marker heterozygosity (Dij) with hybrid performance (μ ij) and combining ability was examined. For a simple genetic model involving uncorrelated parental allele frequencies and complete coverage of quantitative trait loci (QTL) by molecular markers, the correlations between μ ij and Dij were ≤0.25. μ ij and Dij were partitioned into general and specific effects. The expected correlation between specific combining ability and specific molecular marker heterozygosity is high. Expected correlations between general combining ability and general molecular marker heterozygosity are either positive or negative, depending on allele frequencies in the tester lines. Computer simulation was used to investigate a more complex but more realistic genetic model involving incomplete coverage of QTL by molecular markers. All of the following conditions are necessary for effective prediction of hybrid performance based on molecular marker heterozygosity: (1) dominance effects are strong; (2) allele frequencies at individual loci in the parental inbreds are negatively correlated; (3) trait heritability is high; (4) average parental allele frequencies vary only within a narrow range; (5) at least 30-50% of the QTL are linked to molecular markers; and (6) not more than 20-30% of the molecular markers are randomly dispersed or unlinked to QTL.

Journal ArticleDOI
TL;DR: Randomly amplified polymorphic DNA (RAPD) markers have been used to characterise cocoa clones representing the three main cultivated subpopulations: Criollo, Forastero and Trinitario to evaluate germplasm and cocoa improvement programmes.
Abstract: Randomly amplified polymorphic DNA (RAPD) markers have been used to characterise cocoa clones representing the three main cultivated subpopulations: Criollo, Forastero and Trinitario. The use of single primers of arbitrary nucleotide sequence resulted in the selective amplification of DNA fragments which were unique to the individual cocoa clones studied. The use of a single primer allowed each of the clones evaluated to be unequivocally characterised. The application of RAPD markers for the evaluation of germplasm and cocoa improvement programmes are discussed.

Journal ArticleDOI
TL;DR: RFLP analysis showed that the gene is linked to a single-copy DNA clone, RG28, on chromosome 8, at a distance of 4.5 cM, suggesting the availability of a linked DNA marker may facilitate early selection for the aroma gene in rice breeding programs.
Abstract: We report here the identification of a DNA marker closely linked to a gene for aroma in rice. The DNA marker was identified by testing 126 mapped rice genomic, cDNA, and oat cDNA, clones as hybridization probes against Southern blots, consisting of DNA from a pair of nearly isogenic lines (NILs) with or without the aroma gene. Chromosomal segments introgressed from the donor genome were distinguished by RFLPs between the NILs. Linkage association of the clone with the gene was verified using an F3 segregating for aroma. Cosegregation of the scented phenotype and donor-derived allele indicated the presence of linkage between the DNA marker and the gene. RFLP analysis showed that the gene is linked to a single-copy DNA clone, RG28, on chromosome 8, at a distance of 4.5 cM. The availability of a linked DNA marker may facilitate early selection for the aroma gene in rice breeding programs.

Journal ArticleDOI
TL;DR: In rust nursery tests, homozygous lines were more resistant than either parent, if the additional leaf rust gene conditioned an effective of resistance when present singly, may contribute to the durability of leaf rust resistance in cultivars with Lr34.
Abstract: Leaf rust resistance gene Lr34 is present in many wheat cultivars throughout the world that have shown durable resistance to leaf rust. Fourteen pair-wise combinations of Lr34 and seedling leaf rust resistance genes were developed by intercrossing near isogenic 'Thatcher' lines. In both seedling and adult plant tests homozygous paired combinations of specific resistance genes with Lr34 had enhanced resistance relative to either parent to different numbers of isolates that were avirulent to the additional resistance genes. The TcLr34, 18 line also expressed enhanced resistance to specific isolates virulent to Lr18 in seedling and adult plant stages. In rust nursery tests, homozygous lines were more resistant than either parent, if the additional leaf rust gene conditioned an effective of resistance when present singly. The ability of Lr34 to interact with other genes conditioning effective resistance may contribute to the durability of leaf rust resistance in cultivars with Lr34.

Journal ArticleDOI
TL;DR: Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops and showed stable transmission of the chimeric tfdA gene and production of active 2, 4-D monooxygenase.
Abstract: To reduce damage by drift-levels of the herbicide 2,4-dichlorophenoxyacetic acid, we have engineered the 2,4-D resistance trait into cotton (Gossypium hirsutum L.). The 2,4-D monooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5 was isolated, modified and expressed in transgenic tobacco and cotton plants. Analyses of the transgenic progeny showed stable transmission of the chimeric tfdA gene and production of active 2,4-D monooxygenase. Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops.

Journal ArticleDOI
TL;DR: Analysis of RAPD data appears to be helpful in determining the genetic relationships among genotypes, with a higher similarity among T. monococcum than T. urartu.
Abstract: The genetic diversity of two diploid wheat species, Triticum monococcum and Triticum urartu (2n=2x=14), was assessed using random primers and the polymerase chain reaction (PCR). Electrophoretic analysis of the amplification products revealed a higher incidence of polymorphism in T. urartu than T. monococcum. Pair-wise comparisons of unique and shared polymorphic amplification products, were used to generate Jaccard's similarity coefficients. These were employed to construct phenograms using an unweighted pair-group method with arithmetical averages (UPGMA). The UPGMA analysis indicated a higher similarity among T. monococcum than T. urartu. Analysis of RAPD data appears to be helpful in determining the genetic relationships among genotypes.

Journal ArticleDOI
TL;DR: RAPDs were valuable in detecting contaminants and, therefore, in assessing the validity of controlled crosses andLimitations of the technique are discussed in relation to the determination of parental genotypes and construction of linkage maps for hardwood species.
Abstract: Molecular markers are currently being developed for Betula alleghaniensis Britton using random amplified polymorphic DNA (RAPD). Arbitrarily designed 11-mer primers were tested on three intraspecific controlled crosses for which more than 15 full-sibs were available. Using two of these primers, we were able to genetically characterize a total of nine polymorphic RAPD markers. Segregation of these markers was consistent with a biparental diploid mode of inheritance, and all appeared dominant. RAPDs were valuable in detecting contaminants and, therefore, in assessing the validity of controlled crosses. Limitations of the technique are discussed in relation to the determination of parental genotypes and construction of linkage maps for hardwood species.

Journal ArticleDOI
TL;DR: It is proposed that there is a major gene (or genes) in this region in A188 that promotes embryogenic callus initiation and plant regeneration in B73, Mo17, and probably many other recalcitrant inbred lines of maize.
Abstract: The frequency of initiation of friable, embryogenic callus from immature embryos of the elite maize inbred line B73 was increased dramatically by introgression of chromosomal segments from the inbred line A188 through classical backcross breeding. Less than 0.2% of the immature B73 embryos tested (5 of 3,710) formed embryogenic callus. The breeding scheme consisted of six generations of backcrossing to B73 with selection at each generation for high frequency initiation of embryogenic cultures. BC6 individuals were selfed for four generations to select homozygous lines. The average embryogenic culture initiation frequency increased to 46% (256/561). Nearly all (91%) of the embryos from one BC6 S4 plant formed embryogenic cultures. RFLP analysis was used to determine the locations and effects of the introgressed A188 chromosomal segments. Five segments were retained through at least the fifth backcross generation. The hypothesis that one or more of these five regions contains genes controlling somatic embryogenesis in maize was tested using an F2 population of the cross A188 X Mo17. A set of five DNA markers (three of them linked) explained 82% of the observed phenotypic variance for percentage of immature embryos forming embryognic callus. Four of the five markers were located in or near introgressed A188 chromosome segments.The region marked by probe c595 on the long arm of chromosome 9 was highly associated with several measures of in vitro culture response (percent embryogenic embryos, plants per embryo, and plants per embryogenic embryo). We propose that there is a major gene (or genes) in this region in A188 that promotes embryogenic callus initiation and plant regeneration in B73, Mo17, and probably many other recalcitrant inbred lines of maize.

Journal ArticleDOI
TL;DR: This is the first demonstration that a proportion of RAPD markers are not inherited in a dominant fashion, meeting Mendelian expectations in haploid and diploid progeny.
Abstract: The polymerase chain reaction (PCR) was used to generate random amplified polymorphic DNA (RAPD) from honey bee DNA samples in order to follow the patterns of inheritance of RAPD markers in a haplodiploid insect. The genomic DNA samples from two parental bees, a haploid drone and a diploid queen, were screened for polymorphism with 68 different tennucleotide primers of random sequence. Parents were scored for the presence or absence of individual bands. An average of 6.3 bands and 1.3 polymorphisms for presence/absence were observed per primer between the parents. Thirteen of these primers were used to determine the inheritance of RAPD marker alleles in the resulting progeny and in haploid drones from a daughter queen. Four types of polymorphisms were observed. Polymorphisms for band presence/absence as well as for band brightness were inherited as dominant markers, meeting Mendelian expectations in haploid and diploid progeny. Polymorphisms for fragment-length were also observed. These segregated in a near 1∶1 ratio in drone progeny. The last type of polymorphism was manifested as a diploid-specific band. Mixing of amplification products after PCR showed that the diploid-specific band was the result of heteroduplex formation from the DNA of alternate alleles in heterozygotes. In two of the four cases of heteroduplex formation, the alternative alleles were manifested as small fragment-length polymorphisms, resulting in co-dominant markers. This is the first demonstration that a proportion of RAPD markers are not inherited in a dominant fashion.

Journal ArticleDOI
TL;DR: A general and flexible mixture model is proposed for mapping quantitative trait loci by using molecular markers and makes it possible to analyse non-normally distributed traits such as lifetimes, counts or percentages in addition to normally distributed traits.
Abstract: In a segregating population a quantitative trait may be considered to follow a mixture of (normal) distributions, the mixing proportions being based on Mendelian segregation rules. A general and flexible mixture model is proposed for mapping quantitative trait loci (QTLs) by using molecular markers. A method is discribed to fit the model to data. The model makes it possible to (1) analyse non-normally distributed traits such as lifetimes, counts or percentages in addition to normally distributed traits, (2) reduce environmental variation by taking into account the effects of experimental design factors and interaction between genotype and environment, (3) reduce genotypic variation by taking into account the effects of two or more QTLs simultaneously, (4) carry out a (combined) analysis of different population types, (5) estimate recombination frequencies between markers or use known marker distances, (6) cope with missing marker observations, (7) use markers as covariables in detection and mapping of QTLs, and finally to (8) implement the mapping in standard statistical packages.