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A E Melchinger

Publications and source records attributed to A E Melchinger.

26 records · Page 2Linked to original sources
PubMed2002

Genetic diversity in Arabidopsis thaliana L. Heynh. investigated by cleaved amplified polymorphic sequence (CAPS) and inter-simple sequence repeat (ISSR) markers.

In this study, we investigated genetic diversity among 37 accessions in Arabidopsis thaliana from Eurasia, North Africa and North America using morphological traits and two polymerase chain reaction (PCR)-based marker systems: cleaved amplified polymorphic sequences (CAPS) and inter-simple sequence repeats (ISSR). Cluster analysis based on genetic similarities calculated from CAPS data grouped the accessions roughly according to their geographical origin: one large group contained accessions from Western, Northern and Southern Europe as well as North Africa, a second group consisted of Eastern European and Asian continental accessions. North American accessions were interspersed into these groups. Contrary to the CAPS analysis, the dendrogram obtained from the ISSR data did not reflect the geographical origin of the accessions, and the calculated genetic distances did not match the CAPS results. This could be attributable to an uneven genomic distribution of ISSR markers as substantiated by a database search for ISSR binding sites in A. thaliana genomic DNA sequence files, or to the ISSR's different mode of evolution. We recommend CAPS markers for diversity analysis in A. thaliana because a careful selection of markers can ascertain an even representation of the entire genome.

Arabidopsis↗
PubMed2001

The length of the intact donor chromosome segment around a target gene in marker-assisted backcrossing.

Recurrent backcrossing is an established procedure to transfer target genes from a donor into the genetic background of a recipient genotype. By assessing the parental origin of alleles at markers flanking the target locus one can select individuals with a short intact donor chromosome segment around the target gene and thus reduce the linkage drag. We investigated the probability distribution of the length of the intact donor chromosome segment around the target gene in recurrent backcrossing with selection for heterozygosity at the target locus and homozygosity for the recurrent parent allele at flanking markers for a diploid species. Assuming no interference in crossover formation, we derived the cumulative density function, probability density function, expected value, and variance of the length of the intact chromosome segment for the following cases: (1) backcross generations prior to detection of a recombinant individual between the target gene and the flanking marker; (2) the backcross generation in which for the first time a recombinant individual is detected, which is selected for further backcrossing; and (3) subsequent backcross generations after selection of a recombinant. Examples are given of how these results can be applied to investigate the efficiency of marker-assisted backcrossing for reducing the length of the intact donor chromosome segment around the target gene under various situations relevant in breeding and genetic research.

Alleles↗
PubMed2001

Influence of genetic background and heterozygosity on meiotic recombination in Arabidopsis thaliana.

Plant breeding relies on genetic variability generated by meiotic recombination. Control of recombination frequencies is not yet possible, but would significantly extend the options for plant-breeding strategies. A prerequisite would be variability of recombination frequencies. In this study, 15 transgenic kanamycin (KR) and hygromycin (HR) resistance gene insertions mapping to the five Arabidopsis thaliana chromosomes were used as genetic markers. Recombination frequencies were determined from the frequencies of resistance phenotypes within populations segregating for linked KR and HR markers. Recombination frequencies of marker pairs were compared among these four ecotypes, among F1s in both reciprocal forms derived from these ecotypes, and between F1s and their parent lines. On average, the recombination frequencies in F1 crosses were substantially higher (up to 2-fold) than in the homozygous parental ecotypes. A strong negative correlation between genetic similarities of ecotypes and recombination frequencies was detected for two adjacent marker pairs located on the long arm of chromosome 3, but not for marker pairs in other genomic regions. Our results suggest that heterozygosity influences recombination in plant breeding, and cannot be ignored in genetic mapping of genomes.

Arabidopsis↗
PubMed2000

A high-throughput system for genome-wide measurement of genetic recombination in Arabidopsis thaliana based on transgenic markers.

A high-throughput system for the measurement of recombination frequencies in the genetic model plant, Arabidopsis thaliana, is described. It is based on 21 mono-transgenic isogenic lines harboring antibiotic resistance genes on all five chromosomes. Recombination between pairs of gene insertions in repulsion phase that confer resistance against kanamycin (kan) and hygromycin (hyg) is determined by a phenotypic assay of progeny (DART: Double Antibiotic Resistance Technique). DART allows testing for the influence of numerous environmental and genetic factors, including candidate genes, on recombination frequencies in specific genomic regions as well as the entire genome. Its usefulness is demonstrated by investigating the effects of UV treatment, different temperature and phosphorus supply regimes, and sex on recombination frequencies for all five chromosomes of A. thaliana.

Anti-Bacterial Agents↗
PubMed1999

High-resolution mapping of loci conferring resistance to sugarcane mosaic virus in maize using RFLP, SSR, and AFLP markers.

Sugarcane mosaic virus (SCMV) is one of the most important virus diseases of maize in Europe. Genetic analysis on backcross five (BC5) progeny derived from the cross FAP1360A (resistant) x F7 (susceptible) confirmed that at least two dominant genes, Scm1 and Scm2, are required for resistance to SCMV in the progeny of this cross. With the aid of RFLP and SSR marker analyses, Scm1 was mapped in the region of 8.7 cM between the nucleolus organizer region (nor) and RFLP marker bnl6.29 on the short arm of chromosome 6, while Scm2 was mapped to an interval of 26.8 cM flanked by the RFLP markers umc92 and umc102 near the centromere region of chromosome 3. Both chromosome regions were further enriched for AFLP markers by successful application of a bulked segregant analysis to this oligogenic trait. A total of 23 linked AFLP markers were identified, clustered in chromosome regions adjacent to either Scm1 or Scm2. Seven AFLP markers linked to Scm1 resided within the nor-bnl6.29 interval, and one of them, E3M8-1, showed no recombination with Scm1. Three AFLP markers linked to Scm2 are located between umc92 and umc102.

Chromosome Mapping↗
PubMed1998

Quantitative trait locus (QTL) mapping using different testers and independent population samples in maize reveals low power of QTL detection and large bias in estimates of QTL effects.

The efficiency of marker-assisted selection (MAS) depends on the power of quantitative trait locus (QTL) detection and unbiased estimation of QTL effects. Two independent samples N = 344 and 107 of F2 plants were genotyped for 89 RFLP markers. For each sample, testcross (TC) progenies of the corresponding F3 lines with two testers were evaluated in four environments. QTL for grain yield and other agronomically important traits were mapped in both samples. QTL effects were estimated from the same data as used for detection and mapping of QTL (calibration) and, based on QTL positions from calibration, from the second, independent sample (validation). For all traits and both testers we detected a total of 107 QTL with N = 344, and 39 QTL with N = 107, of which only 20 were in common. Consistency of QTL effects across testers was in agreement with corresponding genotypic correlations between the two TC series. Most QTL displayed no significant QTL x environment nor epistatic interactions. Estimates of the proportion of the phenotypic and genetic variance explained by QTL were considerably reduced when derived from the independent validation sample as opposed to estimates from the calibration sample. We conclude that, unless QTL effects are estimated from an independent sample, they can be inflated, resulting in an overly optimistic assessment of the efficiency of MAS.

Chromosome Mapping↗
PubMed1996

A general algorithm to compute multilocus genotype frequencies under various mating systems.

This paper provides a general method to derive algebraic expressions of genotype frequencies for multiple loci under various mating systems, including random mating, back-crossing, selfing, and full-sib mating. For each mating system, general equations are presented. In the case of three loci, comprehensive tables provide recurrence equations for genotype frequencies under random or self mating, and expected genotype frequencies after two generations of full-sib mating. Our results should prove useful in genetic linkage analysis.

Algorithms↗