Twin models in population genetics.
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Biomedical subjects
Publications and source records attributed to L Gedda.
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Over the past hundred years, since Sir Francis Galton first pointed out its scientific value, the study of twins has considerably widened its scope and significance. Gemellology has come to represent an important branch of human genetics and to be applied to the most diverse fields of biomedical and behavioral research, besides obviously contributing to the study of the specific biological, medical, and psychological aspects of the twin condition. More recently, then, it has in turn originated a new branch of modern genetic research, chronogenetics. Finally, sponsored and coordinated by the Mendel Institute in Rome, an International Society for Twins Studies has developed.
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A chronogenetic analysis of caries has been carried out in a sample of 100 twin pairs (27 MZ, 64 DZ, 9 UZ) aged 3-8 years, taking into account the number of decayed teeth and the intensity and severity of caries. Heritability estimates, calculated for each of the various parameters considered, support the hypothesis of a genetic control of the time of onset of caries.
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Whereas the existence of some genetic factor underlying the phenomenon of twinning is almost generally accepted with respect to DZ twins, no such agreement exists with respect to MZ twins. The possible existence of genetic factors underlying MZ twinning has been verified through an analysis of segregation in the sibships of MZ twins and in those of their parents, carried out on a sample of 57 MZ twin pairs (30 M and 27 F). Haldane's a priori method has been applied, considering the sample as obtained through a complete and through an incomplete ascertainment. The results may lead to cautiously confirm the hypothesis of some genetic conditioning of MZ twinning.
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Monozygotic twins are the best witnesses of the existence of a hereditary biological time, because they would not be identical if they had not also inherited the times of appearance and duration of their common hereditary information. The authors gave the name "chronogenetics" to this branch of genetics which concerns the temporal dimension of the gene and the mechanisms of transmission and manifestation of the temporal characteristics. The "Ergon/Chronon System" is suggested as a model to explain chronological heredity in terms of molecular genetics. An example is offered of a chronogenetic analysis of puberty based on the study of puberty times in 157 female and 154 male twin pairs. This shows the hereditary conditioning of numerous chronogenetic parameters, the extrapolation of conclusions concerning the phenomenon of puberty, and the establishment, in this regard, of a borderline between hereditary and physical times. A picture is finally drawn exemplifying Normal Hereditary Times (gametic, auxologic, homeostatic, and old-age recession times) and Pathological Hereditary Times (auxologic, cardiovascular, neoplastic, immunitary, metabolic, and antitoxic pathology times). Provisional chronogenetic developments are indicated, and a possible advancement toward the recycling of the gene is hoped for.
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