Biomedical subjects

Paolo Menozzi

Publications and source records attributed to Paolo Menozzi.

3 recordsLinked to original sources

PubMed2006

A simple general method to evaluate intra-specific transpiration parameters within and among seedling families.

A method to evaluate the genetic control of plant response to increasing soil water deficit is proposed. A description of single tree transpiration behavior was obtained considering parameters independent from air and soil conditions. We removed environmental effects by using two approaches: the normalization of drought data to control (watered) plants and the fitting of a process model. We analyzed the transpiration of 475 4-year-old European beech seedlings, belonging to eight full-sib families. Approximately, one-third of the seedlings were kept in well-watered conditions while the others were exposed to drought for 14 days. Daily plant transpiration was estimated as the difference between two subsequent gravimetric measurements. A mechanistic model was fitted to transpiration data separately for each tree. In the model, the relationship of transpiration with vapor pressure deficit and soil water deficit of each tree is modulated by three parameters: maximum leaf conductance (gM1), maximum transpiration in well-watered soil conditions E(M0)1 and a parameter describing stomatal sensitivity to soil water deficit (c). The model successfully fitted most single tree data and a distribution of estimates for the three parameters (gM1, E(M0)1 and c) was obtained. Predicted transpiration values were in good agreement with observed data (R (2) = 0.86). The model approach produced parameters significantly correlated with those of the "normalization to control" approach. Estimated parameters vary considerably among trees, suggesting the presence of individual differences in stomatal behavior and response to drought. In spite of a large among tree (within family) variation, the among families component for gM1, E(M0)1 and c explained 9.5, 3.3 and 0.1% of total parameters variation suggesting a significant genetic control of transpiration processes.

Fagus↗

PubMed2003

Evidence of recombination in putative ancient asexuals.

Ancient asexuals have been considered to be a contradiction of the basic tenets of evolutionary theory. Barred from rearranging genetic variation by recombination, their reduced number of gene arrangements is thought to hamper their response to changing environments. For the same reason, it should be difficult for them to avoid the build-up of deleterious mutations. Several groups of taxonomically diverse organisms are thought to be ancient asexuals, although clear evidence for or against the existence of recombination events is scarce. Several methods have recently been developed for predicting recombination events by analyzing aligned sequences of a given region of DNA that all originate from one species. The methods are based on phylogenetic, substitution, and compatibility analyses. Here we present the results of analyses of sequence data from different loci studied in several groups of evolutionarily distant species that are considered to be ancient asexuals, using seven different types of analysis. The groups of organisms were the arbuscular mycorrhizal fungi (Glomales), Darwinula stevensoni (Darwinuloidea crustacean ostracods) and the bdelloid rotifers (Bdelloidea), which are thought to have been asexual for the last 400, 25-100, and 35-40 Myr, respectively. The seven different analytical methods evaluated the evolutionary relationships among haplotypes, and these methods had previously been shown to be reliable for predicting the occurrence of recombination events. Despite the different degree of genetic variation among the different groups of organisms, at least some evidence for recombination was found in all species groups. In particular, predictions of recombination events in the arbuscular mycorrhizal fungi were frequent. Predictions of recombination were also found for sequence data that have previously been used to infer the absence of recombination in bdelloid rotifers. Although our results have to be taken with some caution because they could signal very ancient recombination events or possibly other genetic variation of nonrecombinant origin, they suggest that some cryptic recombination events may exist in these organisms.

Animals↗

PubMed2002

Spatial autocorrelation and linkage of Mendelian RAPD markers in a population of Picea abies Karst.

The spatial clustering of single- and di-locus genotypes in a natural, continuous population of Norway spruce was investigated using 69 Mendelian Random Amplified Polymorphic DNA (RAPD) markers that covered about 15 of the species genome, and whose linkage relationships were known. Spatial autocorrelation techniques and randomization tests, applied to both single- and di-locus genotypes, revealed a weak, though significant, spatial structure at the scale 0-200 m (5 of single-locus and 7 of di-locus genotypes). To assess the relative importance of isolation by distance and linkage between markers on their spatial genetic structuring, we grouped joins between sampled trees into equivalence categories expected to show similar, specific patterns of spatial distribution under isolation by distance. Results from both single- and di-locus analyses were consistent with the existence of patches of like homozygotes (about 8 and 11 of loci at the single- and di-locus level, respectively) surrounded by a mix of like heterozygotes. Similar structuring has been predicted by simulation models under isolation by distance and selective neutrality. Overall, linkage between markers accounted for an increase of spatial clumping of di-locus genotypes involving tightly linked loci with recombination fractions up to 0.1, a consequence of limited, stochastic spread of single-locus genotypes in space. Our results support the hypothesis that isolation by distance and linkage have a small, though significant, effect even within continuous forest tree populations. In general, the spatial distribution of multilocus genotypes within populations should be interpreted with caution when linkage relationships among the markers used are unknown.

DNA↗