Carla Rossi

Populational interactions among underdominant chromosome rearrangements help them to persist in small demes

Populational interactions among unlinked chromosomal rearrangements with partial heterozygote sterility and multiplicative fitness were studied to verify whether they help such rearrangements to persist in small populations, in spite of a considerable migration rate with a large population. A deterministic island‐continent model was studied by exact recurrence relations connecting gametic frequencies in successive generations.

Asymptotic behaviour of the mean of a phenotypic diffusion process

Asymptotic genotypic frequencies are evaluated as functions of selection parameters and initial conditions of a phenotypic diffusion process. On the basis of asymptotic relations between genotypic frequencies some analytic results about equilibrium are obtained.

Reduction of neutral gene flow due to the partial sterility of heterozygotes for a linked chromosome mutation

The effect of linkage between a chromosome mutation producing partially sterile heterozygotes and a neutral locus in reducing the gene flow at the neutral locus is studied using a two-population deterministic model. Chromosome mutations are more efficient in reducing gene flow with low migration rates than with high ones. The interaction between high values of partial heterozygote sterility and low recombination rates can produce, in the low migration pattern, a drastic reduction of gene flow. Nevertheless, since only chromosome mutations with low values of partial heterozygote sterility are likely to be involved in chromosomal speciation, a significant reduction of gene flow will probably occur only for a very limited part of the genome. Therefore, a single chromosome mutation is unlikely to play a primary role in speciation.

Equilibrium stability of a diffusion process in population genetics

De Finetti introduced a model of a continuously reproducing population with phenotypic assortative mating for a pair of dominant-recessive autosomal genes. In this paper it is rigorously proved that this model admits of stable equilibria which lie above the Hardy--Weinberg parabola in the de Finetti diagram.

A stochastic model of the genetic predisposition to ageing: an application to twin data.

In previous papers a stochastic model of the ageing process has been proposed. Some genetic parameters (redundance, repair) have been used to explain the observed differential predisposition to the process and family heredity. Because the process is basically due to effective random mutations, any individual of the population would be predisposed differently to ageing according to the structure of his/her genome. In the present paper, the previous model is generalized to take into account an additional genetic parameter, namely, the stability against random mutations, defined as the probability that a random mutation in a codon would produce no mutation in the corresponding protein. Estimation problems connected with the model are approached on the basis of twin data in maximum likelihood estimation as well as in bayesian framework. Some comparisons between the two methods are reported.

Fertility as a function of the woman's age and year of birth in Italy",

A mathematical model is suggested to represent the trend of the fertility coefficient in the Italian woman as a function of her age and year of birth. The study has been based on data from the fertility tables by Livi Bacci-Santini interpreted by one single formula.