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C Matessi

Publications and source records attributed to C Matessi.

10 recordsLinked to original sources
PubMed1999

DNA fingerprinting data and the analysis of population genetic structure by comparing band-sharing patterns.

Genetic isolation among populations can be effectively investigated by multilocus DNA fingerprinting. If populations have diverged, it is expected that the mean proportion of bands shared by individuals from the same population, Bw, exceeds the corresponding mean, Bb, calculated from pairs of individuals from distinct populations. A problem arises in deciding whether any difference between Bw and Bb is statistically significant. In fact, any two band-sharing data (bij), contributing to Bw or Bb, are not independent if they share a common individual (like bij and bjl). This prevents a correct application of parametric tests, such as the Student's t-test. Recently, a modification of this test has been proposed that should avoid the independence problem. Using a large number of samples of fingerprints, simulated from an appropriate 'genetic' model, under a wide range of conditions, we compared the performances of the Student's t-test, the modified t-test and five new permutation tests, where individuals, rather than bij values, are permuted. We found that: (i) the Student's t-test can be very permissive, rejecting too often the null hypothesis when true, but is correct or conservative in certain cases; (ii) the modified t-test is extremely conservative when the null hypothesis is true and very inefficient otherwise; (iii) all five permutation tests are strictly correct, provided that individuals are ordered randomly on gels; and (iv) in this case, the permutation tests are equally efficient, and are not inferior to the Student's t-test when the latter is approximately correct and provides a fair benchmark.

DNA Fingerprinting↗
PubMed1998

Canalization, genetic assimilation and preadaptation. A quantitative genetic model.

We propose a mathematical model to analyze the evolution of canalization for a trait under stabilizing selection, where each individual in the population is randomly exposed to different environmental conditions, independently of its genotype. Without canalization, our trait (primary phenotype) is affected by both genetic variation and environmental perturbations (morphogenic environment). Selection of the trait depends on individually varying environmental conditions (selecting environment). Assuming no plasticity initially, morphogenic effects are not correlated with the direction of selection in individual environments. Under quite plausible assumptions we show that natural selection favors a system of canalization that tends to repress deviations from the phenotype that is optimal in the most common selecting environment. However, many experimental results, dating back to Waddington and others, indicate that natural canalization systems may fail under extreme environments. While this can be explained as an impossibility of the system to cope with extreme morphogenic pressure, we show that a canalization system that tends to be inactivated in extreme environments is even more advantageous than rigid canalization. Moreover, once this adaptive canalization is established, the resulting evolution of primary phenotype enables substantial preadaptation to permanent environmental changes resembling extreme niches of the previous environment.

Adaptation, Physiological↗
PubMed1996

Long-term evolution of multilocus traits.

We analyze monomorphic equilibria of long-term evolution for one or two continuous traits, controlled by an arbitrary number of autosomal loci and subject to constant viability selection. It turns out that fitness maximization always obtains at long term equilibria, but in the case of two traits, linkage determines the precise nature of the fitness measure that is maximized. We then consider local convergence to long term equilibria, for two multilocus traits subject to either constant or frequency dependent selection. From a model of long-term dynamics near an equilibrium we derive a criterion of local long-term stability for 2-dimensional equilibria. It turns out that mutation can be a decisive factor for stability.

Animals↗
PubMed1995

A family of rapidly evolving genes from the sex reversal critical region in Xp21.

Patients with an intact SRY gene and duplications of portions of Xp21 develop as phenotypic females. We have recently mapped this sex reversal locus, DSS, to a 160-kb region of Xp21 that includes the adrenal hypoplasia congenita locus. To clone the gene(s) underlying DSS and AHC, we isolated expressed sequences from the region. Here we describe the characterization of two related genes. DAM10 and DAM6, expressed in adult testis and lung tumors. The predicted DAM10 and DAM6 proteins are 66% identical and are both highly similar to the MAGE family of tumor-associated antigens and to mouse necdin. Genes belonging to the MAGE superfamily, DAMs, MAGEs, and necdin, are likely to have originated from a common ancestor and to be subject to an unusually rapid evolution. The tumor-restricted expression of DAM proteins and their structural similarity to MAGE genes suggest that DAM peptides may be targets for active immunotherapy in lung cancer patients.

Adult↗
PubMed1984

On the evolution of altruism by kin selection.

A general model for the evolution of altruism is formulated. Central to the model is a pair of local fitness functions, which prescribe the fitness of the altruist and selfish phenotypes as functions of the composition of local groups into which prereproductives are subdivided. When the local groups are sibships or other kin groups, the model is one for kin selection. Functions for cost and benefit of altruism are derived from the fitness functions. Conditions for evolution of altruism are then determined in terms of cost and benefit. It is shown that the Hamilton rule has quantitative validity only in the special case of linear fitness functions. Sufficient conditions are found for qualitative validity of the Hamilton rule. Qualitative violation of the rule is also possible.

Journal Article↗
PubMed1981

Coevolution of species in competition: a theoretical study.

A model is presented for the coevolution of several species in competition, each species being genetically variable at one locus with respect to this competition. A function was fund that is maximized during coevolution. This maximization principle was used in order to study the result of competition for a single resource on the utilization functions of the species competing for that resource. In particular, the conditions under which ecological character displacement can evolve were examined.

Animals↗