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Genetica e genomica. Vol. I Genetica generale
No full textL'opera, suddivisa in tre tomi, è destinata agli studenti universitari della Facoltà di Agraria, più direttamente interessati alla genetica ed al miglioramento genetico degli organismi vegetali ed animali, e a quelli delle Facoltà di Scienze Biologiche e Naturali che desiderino integrare la loro preparazione in genetica, genomica e biotecnologie genetiche con lo studio di alcuni aspetti più propriamente connessi alle specie di interesse agrario-alimentare ed ambientale. Tuttavia, il testo è facilmente consultabile anche da tutti i tecnici del settore agrario che desiderino avvicinarsi, in particolare, alle basi teoriche ed ai concetti generali della genetica ed aggiornarsi sui problemi del miglioramento genetico, della costituzione varietale, delle produzioni alimentari, dell'analisi genomica e delle biotecnologie genetiche, più in generale
Genetica e genomica. Vol. 2 Miglioramento genetico
No full textL'opera, suddivisa in tre tomi, è destinata agli studenti universitari della Facoltà di Agraria, più direttamente interessati alla genetica ed al miglioramento genetico degli organismi vegetali ed animali, e a quelli delle Facoltà di Scienze Biologiche e Naturali che desiderino integrare la loro preparazione in genetica, genomica e biotecnologie genetiche con lo studio di alcuni aspetti più propriamente connessi alle specie di interesse agrario-alimentare ed ambientale. Tuttavia, il testo è facilmente consultabile anche da tutti i tecnici del settore agrario che desiderino avvicinarsi, in particolare, alle basi teoriche ed ai concetti generali della genetica ed aggiornarsi sui problemi del miglioramento genetico, della costituzione varietale, delle produzioni alimentari, dell'analisi genomica e delle biotecnologie genetiche, più in generale
Apomictic seed production in Poa pratensis L.: towards the understanding of its genetic control.
No full textOsservare, comprendere il bambino e agire il cambiamento. Uno strumento per il docente di scuola primaria
No full textL'eterosi nelle piante: dall'ipotesi genetica di Jones all'era genomica. Parte II: Blocchi cromosomici e basi genetiche dell'eterosi.
No full textChromosome blocks are the genomic units of genetic transmission in sexually reproducing plants. Breeders work with chromosome blocks, not individual genes in their selection programs. Thus, chromosome blocks support heterosis and affect estimates of gene action and interaction. Chromosome blocks vary in size according to the intensity of linkage and so the frequency of recombination, the number of sexual generations (i.e., the approach to linkage equilibrium) and the position of crossing-over sites. Even in the transfer of simple traits by backcross strategies, the amount of undesirable genetic material associated to the gene of interest is usually not known, situation often referred as linkage drug.
D.F. Jones clearly recognized the role of chromosome blocks in 1917 when he proposed the dominance of linked factors as a means of accounting for heterosis. The proposition is elegant because it acknowledges the cumulative effect of linked dominant genes as transmission units. In the following years there was much debate about gene action, and heterosis was sometimes interpreted as true overdominance, that is single loci at which the heterozygous phenotype exceeds that of both homozygotes.
Maize researchers were careful to point out that estimates of dominance variance exceeding that for straight dominance could be due to either overdominance or linkage disequilibrium of linked loci with favourable alleles in repulsion phase (pseudo-overdominance). Degrees of dominance in F2 populations in linkage disequilibrium was compared with populations in F8 through F16 in linkage equilibrium. Estimates for degree of dominance decreased with the approach to linkage equilibrium indicating that the initial heterosis was more likely due to linked dominant factors in linkage disequilibrium than to true overdominance.
In autotetraploid alfalfa, E.T. Bingham reached the same conclusion from results indicating linked dominant factors in chromosome blocks, and not multiple gene interactions, as the basis for progressive heterosis. On the whole, genetic data so far collected indicate that superior dominant alleles at different loci complement each other by masking deleterious recessive alleles at the respective loci.
The cumulative action of genes in chromosome blocks not only explains the breeding behaviour of diploid crops, but also explains the fixation of transgressive traits in self-pollinated allopolyploids and the relatively high levels of heterosis maintained in cross-pollinated autopolyploids.
Thus, chromosome blocks provide an efficient model to explain heterosis and a unifying concept for all categories of plants
L'eterosi nelle piante: dall'ipotesi genetica di Jones all'era genomica. Parte III: Analisi dell'eterosi a livello molecolare.
No full textWith the advent of the genomic era and biotechnology, the technical tools to establish the molecular basis of heterosis are at hand. Some important data are emerging from the fog. Studies at the genome, transcriptome and proteome levels in model species have led to unexpected results. Although allelic sequences can vary extensively in a given genome, it was generally assumed that each gene in one individual should have an allelic counterpart in another individual of the same species. Violation of genetic microcolinearity was reported in maize and potentially related both to the classification of heterotic groups and to the manifestation of hybrid vigor in this species. Moreover, allelic expression variation of fundamental genes has recently been uncovered in mouse and maize hybrids. Most of the investigated genes showed differences at the messenger level, ranging from unequal expression of the two alleles (biallelic) to expression of a single allele (monoallelic). Changes in mRNA expression levels and allele-specific transcript ratios were attributed mainly to differences in noncoding DNA sequences (i.e. cis- and trans-acting elements). Epigenetic regulation and parental imprinting had minimal effects. One of the most important finding was that genetically improved modern hybrids of maize express both alleles at each locus, whereas less improved old hybrids frequently show monoallelic expression. Furthermore, the two alleles in the hybrids respond differently in plant tissues and to environmental conditions. The allele-specific expression and variation in different tissues in responding to stress suggest an unequivalent function of the parental alleles in the hybrids. Additional studies on gene dosage effects in either diploids or polyploids revealed that the expression of many genes, in terms of transcripts and proteins, does not exhibit the midparent value expected in case of additive gene action. Overall results indicated that allele dosage effects can play important roles in determining phenotypic diversity and have also impacts on hybrid vigor. Since housekeeping genes that encode metabolic functions usually show a greater degree of dominant/recessive behaviour between allelic alternatives and are believed less influenced by dosage effects, it has been argued that dosage effects are a reflection of the dosage dependence of most regulatory genes. Following this train of thought, researchers are led to the idea that heterosis might be the result of different alleles being present at loci that contribute hierarchically to the regulatory networks controlling quantitative traits. Real-Time PCR and DNA microarray analyses will shed light in this fascinating area and might be able to provide some answers about the spectrum of genes that show regulated changes of expression patterns in hybrids. An eventual molecular explanation of heterosis will determine whether it can be manipulated in crop plants for the benefit of agriculture
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