Genetic linkage maps reveal the order of markers based on the frequency of recombination between markers during meiosis. Because the rate of recombination varies along chromosomes, it has been difficult to relate linkage maps to chromosome structure. Here we use cytological maps of crossing over based on recombination nodules (RNs) to predict the physical position of genetic markers on each of the 10 chromosomes of maize. This is possible because (1) all 10 maize chromosomes can be individually identified from spreads of synaptonemal complexes, (2) each RN corresponds to one crossover, and (3) the frequency of RNs on defined chromosomal segments can be converted to centimorgan values. We tested our predictions for chromosome 9 using seven genetically mapped, single-copy markers that were independently mapped on pachytene chromosomes using in situ hybridization. The correlation between predicted and observed locations was very strong (r 2 ϭ 0.996), indicating a virtual 1:1 correspondence. Thus, this new, high-resolution, cytogenetic map enables one to predict the chromosomal location of any genetically mapped marker in maize with a high degree of accuracy. This novel approach can be applied to other organisms as well.
INTEGRATING genetic linkage maps with chromoorganized meiotic chromosomes. This is an important point because the observed location of a gene on a some structure has been an important objective ever since it was demonstrated that genes occur in a fixed chromosome (relative to the centromere) can be different on mitotic compared to meiotic chromosomes, as order on chromosomes (Sutton 1903; Bridges 1916).demonstrated by Froenicke et al. (2002) for mouse Linkage maps are defined by the percentage of recombichromosomes. Related observations indicate that differnation between markers [as expressed in centimorgans ences in mitotic and meiotic chromosomes may affect (cM)] and reveal the linear order of markers. However, the relative cytological distance between markers in they do not contain information on the actual physical plants as well (Stack 1984). In this regard, Drosophila distance between markers, whether that distance is exmelanogaster has the best integration of cytological (chropressed as a cytological length (positions on chromomosome), genetic (recombination), and physical (DNA somes) or as a physical length (number of DNA base sequence) aspects of the genome, but this integration pairs). This is because crossing over is not evenly distribis based on somatic polytene chromosomes (http://fly uted along chromosomes. Crossing over is suppressed base.bio.indiana.edu/), not on meiotic chromosomes in heterochromatin and centromeres, and crossing over where crossing over actually occurs. For these reasons, is variable even in euchromatin where most crossing the position of individual genes along meiotic chromoover occurs (Sherman and Stack 1995; Harper and somes and the relation of gene position to meiotic reCande 2000; Anderson et al. 2003). As a result, linkage combination are understood o...
This work is aimed towards the generation of enzyme arrays on electrochemically active surfaces by taking advantage of the DNA-directed immobilization (DDI) technique. To this end, two different types of horseradish peroxidase (HRP)-DNA conjugates were prepared, either by covalent coupling with a bifunctional cross-linker or by the reconstitution of apo-HRP, that is, HRP lacking its prosthetic heme (protoporphyrin IX) group, with a covalently DNA-modified heme cofactor. Both conjugates were characterized in bulk and also subsequent to their immobilization on gold electrodes through specific DNA hybridization. Electrochemical measurements by using the phenolic mediator ortho-phenylendiamine indicated that, due to the high degree of conformational orientation, the apparent Michaelis-Menten constants of the reconstituted HRP conjugate were lower than those of the covalent conjugate. Due to the reversible nature of DDI, both conjugates could be readily removed from the electrode surface by simple washing and, subsequently, the electrodes could be reloaded with fresh enzymes, thereby restoring the initial amperometric-response activity. Moreover, the specific DNA hybridization allowed us to direct the two conjugates to distinct sites on a microelectrode array. Therefore, the self-assembly and regeneration capabilities of this approach should open the door to the generation of arrays of redox-enzyme devices for the screening of enzymes and their effectors.
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