Biomedical subjects

C W Stuber

Publications and source records attributed to C W Stuber.

11 recordsLinked to original sources

PubMed1995

Mapping and manipulating quantitative traits in maize.

Maize has been used effectively as a model organism in the development and evaluation of molecular markers for the identification, mapping and manipulation of major genes affecting the expression of quantitative traits in plants. Although quantitative geneticists have recognized the possibility of major loci, the general dogma had emerged that quantitative traits were controlled by many loci, each with a small effect. This interpretation sent a quantitative traits because it would be essentially impossible to isolate a gene responsible for the trait. Recent results from numerous mapping studies have shown that quantitative traits are controlled by, at least some, factors with major effects, and have given credibility to the conclusion that major loci exist and that one might be able to study them. Positive results from marker-facilitated selection and introgression studies have further strengthened this conclusion.

Chromosome Mapping↗

PubMed1995

Comparative recombination distances among Zea mays L. inbreds, wide crosses and interspecific hybrids.

Recombination distances and linkage heterogeneity were compared among a wide range of maize inbreds, wide crosses and maize x teosinte hybrids. Twelve maize and four teosinte races were backcrossed to stocks fixed for rare marker alleles on chromosome arm 1L. Recombination fraction estimates were higher for exotic germplasm than for either U.S. maize or maize x teosinte crosses. Serrano, Tuxpeño and a US-adapted inbred line of tropical origin, NC300, exhibited enhanced recombination. Three of the four maize x teosinte hybrids had little or no recombination between two loci. The observed recombination "shrinkage" resulted from an apparent inversion in the vicinity of the Amp1 locus. Average recombination distances among common marker loci for composite maps were highly variable, even when map construction was restricted to maize germplasm of similar origins.

Cloning, Molecular↗

PubMed1992

Identification of genetic factors contributing to heterosis in a hybrid from two elite maize inbred lines using molecular markers.

The use of molecular markers to identify quantitative trait loci (QTLs) affecting agriculturally important traits has become a key approach in plant genetics-both for understanding the genetic basis of these traits and to help design novel plant improvement programs. In the study reported here, we mapped QTLs (and evaluated their phenotypic effects) associated with seven major traits (including grain yield) in a cross between two widely used elite maize inbred lines, B73 and Mo17, in order to explore two important phenomena in maize genetics-heterosis (hybrid vigor) and genotype-by-environment (G x E) interaction. We also compared two analytical approaches for identifying QTLs, the traditional single-marker method and the more recently described interval-mapping method. Phenotypic evaluations were made on 3168 plots (nearly 100,000 plants) grown in three states. Using 76 markers that represented 90-95% of the maize genome, both analytical methods showed virtually the same results in detecting QTLs affecting grain yield throughout the genome, except on chromosome 6. Fewer QTLs were detected for other quantitative traits measured. Whenever a QTL for grain yield was detected, the heterozygote had a higher phenotype than the respective homozygote (with only one exception) suggesting not only overdominance (or pseudooverdominance) but also that these detected QTLs play a significant role in heterosis. This conclusion was reinforced by a high correlation between grain yield and proportion of heterozygous markers. Although plant materials were grown and measured in six diverse environments (North Carolina, Iowa and Illinois) there was little evidence for G x E interaction for most QTLs.

Crosses, Genetic↗

PubMed1988

New isozyme systems for maize (Zea mays L.): aconitate hydratase, adenylate kinase, NADH dehydrogenase, and shikimate dehydrogenase.

Electrophoretic variation and inheritance of four novel enzyme systems were studied in maize (Zea mays L.). A minimum of 10 genetic loci collectively encodes isozymes of aconitate hydratase (ACO; EC 4.2.1.3.), adenylate kinase (ADK; EC 2.7.4.3), NADH dehydrogenase (DIA; EC 1.6.99.-), and shikimate dehydrogenase (SAD; EC 1.1.1.25). At least four loci are responsible for the genetic control of ACO. Genetic data for two of the encoding loci, Aco1 and Aco4, demonstrated that at least two maize ACOs are active as monomers. Analysis of organellar preparations suggests that ACO1 and ACO4 are localized in the cytosolic and mitochondrial subcellular fractions, respectively. Maize ADK is encoded by a single nuclear locus, Adk1, governing monomeric enzymes that are located in the chloroplasts. Two cytosolic and two mitochondrial forms of DIA were electrophoretically resolved. Segregation analyses demonstrated that the two cytosolic isozymes are controlled by separate loci, Dia1 and Dia2, coding for products that are functional as monomers (DIA1) and dimers (DIA2). The major isozyme of SAD is apparently cytosolic, although an additional faintly staining plastid form may be present. Alleles at Sad1 are each associated with two bands that cosegregate in controlled crosses. Linkage analyses and crosses with B-A translocation stocks were effective in determining the map locations of six loci, including the previously described but unmapped locus Acp4. Several of these loci were localized to sparsely mapped regions of the genome. Dia2 and Acp4 were placed on the distal portion of the long arm of chromosome 1, 12.6 map units apart. Dia1 was localized to chromosome 2, 22.2 centimorgans (cM) from B1. Aco1 was mapped to chromosome 4, 6.2 cM from su1. Adk1 was placed on the poorly marked short arm of chromosome 6, 8.1 map units from rgd1. Less than 1% recombination was observed between Glu1 (on chromosome 10) and Sad1. In contrast to many other maize isozyme systems, there was little evidence of gene duplication or of parallel linkage relationships for these allozyme loci.

Aconitate Hydratase↗

PubMed1988

Gene mapping with recombinant inbreds in maize.

Recombinant inbred lines of maize have been developed for the rapid mapping of molecular probes to chromosomal location. Two recombinant inbred families have been constructed from F2 populations of T232 X CM37 and CO159 X Tx303. A genetic map based largely on isozymes and restriction fragment length polymorphisms has been produced that covers virtually the entire maize genome. In order to map a new gene, an investigator has only to determine its allelic distribution among the recombinant inbred lines and then compare it by computer with the distributions of all previously mapped loci. The availability of the recombinant inbreds and the associated data base constitute an efficient means of mapping new molecular markers in maize.

Chromosome Mapping↗

PubMed1987

Evidence for multilocus genetic control of preferential fertilisation in maize.

Genetic segregation was studied in more than 1900 seedlings of an F2 between the maize (Zea mays L.) inbred lines T232 and CM37. Significant segregation distortion was observed at 11 of 17 segregating allozyme loci and at a single morphological marker locus distributed on 7 of the 10 chromosomes in the genome. Deviations from genotypic class expectations were small for most loci, and averaged 7.7 per cent. Percent transmission of the allele contributed by T232 varied from 47.7 per cent to 53.3 per cent. The allele donated by T232 was significantly under-represented for loci on chromosomes 1 and 8, whereas the allele contributed by CM37 was deficient for nine of the ten segregating loci on chromosomes 2, 3, and 6. In all cases, the parental origin of the deficient allele was consistent for markers on a chromosome. Evidence is presented that suggests the aberrant ratios arose from linkage of the markers with genetic factors affecting prezygotic transmission, and that a minimum of 5 such factors were operative, one on each of chromosomes 1, 2, 3, 6, and 8. In contrast to the multi-locus and multi-chromosomal distorted segregation observed in the F2, all loci in backcross progenies fit Mendelian expectations. It is suggested that this discrepancy reflects variable environmental selection pressures on genes that influence aspects of gamete competition.

Alleles↗

PubMed1987

Molecular-marker-facilitated investigations of quantitative-trait loci in maize. I. Numbers, genomic distribution and types of gene action.

Individual genetic factors which underlie variation in quantitative traits of maize were investigated in each of two F2 populations by examining the mean trait expressions of genotypic classes at each of 17-20 segregating marker loci. It was demonstrated that the trait expression of marker locus classes could be interpreted in terms of genetic behavior at linked quantitative trait loci (QTLs). For each of 82 traits evaluated, QTLs were detected and located to genomic sites. The numbers of detected factors varied according to trait, with the average trait significantly influenced by almost two-thirds of the marked genomic sites. Most of the detected associations between marker loci and quantitative traits were highly significant, and could have been detected with fewer than the 1800-1900 plants evaluated in each population. The cumulative, simple effects of marker-linked regions of the genome explained between 8 and 40% of the phenotypic variation for a subset of 25 traits evaluated. Single marker loci accounted for between 0.3% and 16% of the phenotypic variation of traits. Individual plant heterozygosity, as measured by marker loci, was significantly associated with variation in many traits. The apparent types of gene action at the QTLs varied both among traits and between loci for given traits, although overdominance appeared frequently, especially for yield-related traits. The prevalence of apparent overdominance may reflect the effects of multiple QTLs within individual marker-linked regions, a situation which would tend to result in overestimation of dominance. Digenic epistasis did not appear to be important in determining the expression of the quantitative traits evaluated. Examination of the effects of marked regions on the expression of pairs of traits suggests that genomic regions vary in the direction and magnitudes of their effects on trait correlations, perhaps providing a means of selecting to dissociate some correlated traits. Marker-facilitated investigations appear to provide a powerful means of examining aspects of the genetic control of quantitative traits. Modifications of the methods employed herein will allow examination of the stability of individual gene effects in varying genetic backgrounds and environments.

Chromosome Mapping↗

PubMed1983

Inheritance, intracellular localization, and genetic variation of phosphoglucomutase isozymes in maize (Zea mays L.).

Phosphoglucomutase (PGM; EC 2.7.5.1) isozyme variants were studied in a large number of inbred lines, crosses, and races of maize (Zea mays L.). Patterns of Mendelian inheritance demonstrated for PGM isozyme variants indicated that they are encoded by nuclear genes. Two unlinked loci, Pgml and Pgm2, located on the long arm of chromosome 1 and the short arm of chromosome 5, respectively, specify the observed electrophoretic variation on starch gels. No intra- or interlocus hybrid bands were found, suggesting that each isozyme band consists of a single polypeptide. PGM isozymes were present in all plant parts studied and the activity specified by both loci appears to reside in the cytoplasm. In studies of 520 racial collections of maize from Latin America, a single allele at each locus predominated in most collections. Likewise, the same alleles predominated in a set of 406 inbred lines of maize from the United States and Canada.

Genetic Variation↗

PubMed1981

Malate dehydrogenase: viability of cytosolic nulls and lethality of mitochondrial nulls in maize.

Five independently inherited loci on five distinct chromosomes encode the mitochondrial and cytosolic isozymes of NAD-dependent malate dehydrogenase (MDH; L-malate:NAD+ oxidoreductase, EC 1.1.1.37). Multiple alleles, including electrophoretic nulls, occur for each locus. However, a single allele of normal activity at one of the three loci encoding the mitochondrial MDHs is sufficient for normal development, whereas plants with essentially no cytosolic MDH activity function normally. The requirement of a normal activity allele at one of the three structural loci encoding the mitochondrial MDHs demonstrates in plants that a commonly studied dehydrogenase enzyme is essential for normal embryogenesis.

Alleles↗

PubMed1977

Genetic control and racial variation of beta-glucosidase isozymes in maize (Zea mays L.)

beta-Glucosidase (beta-D-glucoside glucohydrolase, E.C. 3.2.1.21, beta-Glu) isozyme variants were studied in a large number of inbred lines, crosses, and races of maize (Zea mays L.). The pattern of Mendelian inheritance demonstrated for beta-GLU variants indicated that they are under nuclear gene control. Twenty-two allelic forms at a single locus were identified in the materials studied by starch gel electrophoresis. Genetic data indicate that beta-GLU in maize is functionally a dimer. Variation of beta-GLU isozymes in 51 racial collections of maize from Mexico showed little correlation with morphological or geographical data. In 39 collections from Central America, variation patterns appeared to have some association with altitude.

Alleles↗

PubMedDate not supplied

Duplicated plastid and triplicated cytosolic isozymes of triosephosphate isomerase in maize (Zea mays L.).

We studied electrophoretic variation and inheritance of triosephosphate isomerase (TPI) isozymes in maize (Zea mays L.). In contrast to most diploid plants, in maize, TPI exists as multiple isozymes in both the plastid and cytosolic subcellular compartments. Phenotypes result from the overlay of two independent sets of isozymes and allozymes, representing the plastid (encoded by the nuclear genes Tpi1 and Tpi2) and cytosolic (encoded by Tpi3, Tpi4, and Tpi5) systems. All possible intragenic and intergenic dimeric enzymes are formed between polypeptides within each subcellular compartment. No heterodimers are formed between plastid and cytosolic polypeptides. Extensive surveys of accessions of land races and inbred lines revealed 22 allelic variants for the five loci. Most alleles have been formally validated by segregation analysis. We describe two null alleles at Tpi4, distinguished by their relative abilities to form intergenic heterodimers with polypeptides specified by Tpi3 and Tpi5. Linkage analyses and crosses with B-A translocation stocks were effective in determining the chromosome locations of all five loci. Duplicated genes for both the plastid and cytosolic isozymes were localized to genomic regions that possess numerous other redundant sequences. We placed Tpi1 on the long arm of chromosome 7, approximately 23 centimorgans (cM) distal to g11; we localized its duplicate--Tpi2--17 cM distal to v4 on the long arm of chromosome 2. The triplicate loci encoding cytosolic TPIs reside on chromosomes 3 and 8. Tpi4 is approximately equidistant (11 cM) from d1 and Lg3, near the centromere of chromosome 3. Tpi3 and Tpi5 are located on distal ends of the most poorly marked maize chromosome; Tpi3 is 29 cM distal to Idh 1 on 8L, and Tpi5 is on 8S or near the centromere on 8L. In contrast to most duplicated maize sequences, which often occur in parallel linkages on different chromosomes, Tpi3 and Tpi5 provide an example of intrachromosomal gene duplication. Several of the Tpi loci are located in sparsely mapped regions of the genome, and Tpi1 is the first isozyme marker for chromosome 7.

Alleles↗