On the basis of the parameters of gene stability suggested by Gedda-Brenci's model on the Ergon/Chronon System, a mathematical and a stochastic model of gene decay are worked out.

The models of gene decay, previously worked out on the basis of Gedda-Brenci's Ergon/Chronon System, now undergo an analytic simulation, in order to verify how the mathematical model fits the stochastic one.

The results are presented of a method of generalized distances calculated by a noncentral χ2 test and applied to compare 63 twin pairs and 196 sib pairs. The advantage of this method in biometrical analysis lies in the fact that several measurements can be utilised simultaneously. Besides, it takes into account the distance of each relative to the centre of the population and also has the advantage of permitting the comparison of distances between pairs of relatives whatever their age or sex.

Generalized distances were calculated for four measurements of the head, five of the body and eleven of the face. For all three sets of measurements the influence of genetical factors was demonstrated. The body seems less influenced by environmental factors and more conditioned by genetic ones.

Since the MNS blood group system does not exhaust the total degrees of freedom under the Wright's equilibrium law, it was felt that the peculiar problems facing the detection of F (the fixation coefficient of Wright's model) from ABO blood group data may not be totally relevant to the MNS system. To verify this, a short discussion on the detection of F from MNS blood group data is given here.

Two remarks on Rao's Two-Gene Hypothesis for the inheritance of hypertrichosis of ear rims are offered here. First remark provides justification for the particular location of NH- and H-loci on the sex chromosomes in man. A single-case longitudinal study is also reported, which gives rise to the possibility of testing the two-gene hypothesis on family data.

A genetic study has been carried out on tongue pigmentation in man, based on 10 pedigrees and 39 Indian populations. It is concluded in favour of a genetic basis of the trait, which would be inherited as an autosomal recessive.

The different varieties of congenital dyschromatopsias are inherited following different modes. The dyschromatopsias of the protan and deutan type, as well as the atypical achromatopsia (blue mono-cone monochromacy), are sex-linked recessive, the tritanopia probably autosomal dominant and the typical achromatopsia surely autosomal recessive. The mode of transmission of the tritanomalia is still dubious.

Concerning the localisation of the genes on the X chromosome, the bilocular theory for the deutan and protan genes is accepted at the present time. These genes form a cluster with the genes of hemophilia A and G6PD deficiency. It is possible that this cluster is situated on the short arm of the X chromosome or on the long arm near the centromeric region. The exact situation will be known very soon, when the interpretation of the results of the cellular hybridisation, which are still discordant, will be well established.

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.

Almost one century after Galton's first scientific formulation of the Twin Method, based on the comparison of MZ and DZ twin series, not only twin studies play a fundamental role and the Interzygotic Test is widely applied in human and especially medical genetic research, but new methods have also been worked out, such as the Azygotic Test and the Twin Clinical Method.

Moreover, the study of twins has more recently led to new insights into the study of biological times, with the development of the modern branch of Chronogenetics.