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Consanguinity, Inbreeding, and Genetic Drift in Italy (MPB-39)

Consanguinity, Inbreeding, and Genetic Drift in Italy (MPB-39)

Copyright Date: 2004
Pages: 320
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    Consanguinity, Inbreeding, and Genetic Drift in Italy (MPB-39)
    Book Description:

    In 1951, the geneticist Luigi Luca Cavalli-Sforza was teaching in Parma when a student--a priest named Antonio Moroni--told him about rich church records of demography and marriages between relatives. After convincing the Church to open its records, Cavalli-Sforza, Moroni, and Gianna Zei embarked on a landmark study that would last fifty years and cover all of Italy. This book assembles and analyzes the team's research for the first time.

    Using blood testing as well as church records, the team investigated the frequency of consanguineous marriages and its use for estimating inbreeding and studying the relations between inbreeding and drift. They tested the importance of random genetic drift by studying population structure through demography of the last three centuries, using it to predict the spatial variation of frequencies of genetic markers. The authors find that drift-related genetic variation, including its stabilization by migration, is best predicted by computer simulation. They also analyze the usefulness and limits of the concept of deme for defining Mendelian populations. The genetic effect of consanguineous marriage on recessive genetic diseases and for the detection of dominance in metric characters are also studied.

    Ultimately bringing together the many strands of their massive project, Cavalli-Sforza, Moroni, and Zei are able to map genetic drift in all of Italy's approximately 8,000 communes and to demonstrate the relationship between each locality's drift and various ecological and demographic factors. In terms of both methods and findings, their accomplishment is tremendously important for understanding human social structure and the genetic effects of drift and inbreeding.

    eISBN: 978-1-4008-4727-3
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-viii)
  3. Acknowledgments
    (pp. ix-x)
  4. CHAPTER 1 History of This Investigation and Structure of This Book
    (pp. 1-28)

    The study of inbreeding, the consequence of the mating of relatives, has an important place in genetics. The similarity of the paternal and maternal contributions caused by the mating of relatives leads to increased genetic homogeneity of inbred individuals. A table of the expected effects of inbreeding in successive generations of selfing (crossing with self), the closest mating possible, which often occurs spontaneously in many plants, appears in Mendel’s article, the founding paper of genetics. Thus, Mendel was also the first population geneticist.

    Human societies are unique in keeping records of their own ancestry, sometimes, though very rarely, for thousand...

  5. CHAPTER 2 Customs and Legislation Affecting Consanguineous Marriages, with Special Attention to the Catholic Church
    (pp. 29-38)

    The Catholic Church has taken a position on the issue of consanguineous marriages since its origin. Laws against marriage between relatives existed in the Jewish and Roman tradition. In the Bible, unions between close relatives (brother and sister and brother and half-sister) were severely punished: a public execution is mentioned in Deut. 20:17. Different types of forbidden matings are given by the Bible: a man could not marry his mother (Lev. 18:7), his sister (Lev. 18:12, 20:19), his father’s sister (Lev. 18:12, 20:19), his mother’s sister (Lev. 18:13, 20:19), or his son’s daughter (Lev. 18:10). A man could marry his...

  6. CHAPTER 3 Demographic Factors Affecting the Frequencies of Consanguineous Marriage—A Study in Northern Emilia
    (pp. 39-68)

    The subject of this and the following chapter is the prediction of the frequency of consanguineous marriages of given type and degree, based on the assumption that marrying a consanguineous person takes place randomly. The comparison of these expected frequencies with observed ones allows us to detect possible deviations from randomness, due to preference for or avoidance of consanguineous marriages. The calculation of expected frequencies requires knowledge of certain quantities, mostly of demographic nature. We have been able to secure such knowledge from several sources in or around the Parma diocese, located in northern Emilia, in the middle of the...

  7. CHAPTER 4 Probability of Consanguineous Marriages
    (pp. 69-89)

    In general, two consanguineous individuals of a given pedigree are expected to have a distribution of difference between their ages that depends on the degree of consanguinity and type of pedigree. Some have, on average, an extreme age difference, greater than that which is most common in the general population (and in some cases in opposite direction, as, for example, for aunt and nephew). Pedigrees of even cousins have an expected age difference near zero, and therefore closer to the usual one. In standard, nonconsanguineous marriages, the age of spouses shows a high correlation, the husband being on average older...

  8. CHAPTER 5 Consanguinity, Inbreeding, and Observed Genetic Drift in the Parma Valley
    (pp. 90-121)

    This research originated in the early 1950s and, although some parts of it were published (Cavalli-Sforza 1969, Cavalli-Sforza and Bodmer 1971, 1999, Cavalli-Sforza and Feldman 1990), a complete report never appeared. In fact, it is only very recently that a final evaluation of the results has been made. The project began in 1954, with the idea of collecting data on the genetic diversity of the population inhabiting the villages of a very diverse area, that of the valley of Parma, in which one could distinguish essentially three types of habitat: the towns of the plains and the villages of the...

  9. CHAPTER 6 A Computer Simulation of the Upper Parma Valley Population
    (pp. 122-148)

    The two major problems that we have tried to attack in this volume are the measurement of inbreeding in human populations, through a study of consanguinity, and that of random genetic drift. We have obtained some measurements and developed new methods that have been illustrated in the last three chapters, but we have not yet given a full answer to some major questions.

    It soon became clear that a new approach could be very helpful, that of creating by computer an artificial population as similar as possible to the real one and estimating genetic quantities from it, which could then...

  10. CHAPTER 7 Islands
    (pp. 149-191)

    The Italian Republic has a territory of a little over 301,000 km². This includes 25,400 km² of the island of Sicily (the largest Mediterranean island), plus the Aeolian, Egad, and Pelagian archipelagos, and Ustica and the Pantelleria islands, totaling about 280 km²; as well as 23,800 km² of the island of Sardinia, the next largest, near which are five small islands totaling 256 km². Because of their insular status Sicily and Sardinia have been under a special regime concerning consanguinity dispensations, and therefore they are analyzed separately from the rest of Italy. Sardinia is the better known and is considered...

  11. CHAPTER 8 Effects of Inbreeding on Normal and Pathological Phenotypes
    (pp. 192-210)

    The study of the progeny of consanguineous marriages can provide information on the phenotypic effects of inbreeding. Inbreeding will cause a relative increase of the frequency of homozygous individuals, and therefore is expected to reveal rare recessive traits. Sir Archibald Garrod used this principle to give the first proof of the validity of Mendel’s rules for humans (1902). He showed that patients of certain recessive traits or diseases like albinism, alkaptonuria, and others, which he named “inborn errors of metabolism,” have unusually high frequency in children of consanguineous parents. He correctly hypothesized that these defects were due to the lack...

  12. CHAPTER 9 Consanguineous Marriages in Italy: Data from the Vatican Archives
    (pp. 211-241)

    “Consanguineous marriages in Italy: information gathered from the matrimonial dispensations requested in 1911–1964 of the Sacred Congregation of the Sacraments, stored in the Vatican’s Secret Archives.” This is the title of a set of 44 volumes produced by Antonio Moroni’s work in the 1960s, from which one can study the frequencies, causes, and effects of consanguinity in the whole of Italy over a 54-year period.

    The following information was magnetically filed from each of 520,492 consanguineous marriages for which dispensation was requested:

    Surname and Christian name of husband and wife

    Age at marriage

    Year of marriage

    Name of diocese...

  13. CHAPTER 10 Geography of Demes in Italy
    (pp. 242-283)

    Populations, demes, and random mating are recurrent terms in the population genetics literature. This is a good opportunity for clarifying these concepts and sharpening their meaning.

    Population has a precise statistical definition: it is the source of the samples of individuals that we study. It is important that it is defined carefully enough at the beginning so that if we take another sample from the same population, we can expect it to give the same statistical conclusions obtained from the first. But populations may change over time, and so we can expect only an approximate correspondence between independent samples at...

  14. CHAPTER 11 Conclusions
    (pp. 284-302)

    Consanguineous marriages vary enormously in human populations, under the influence of differences in customs and laws. Unions with the closest relatives (parent–child and sib–sib) are considered incest and punished in almost every culture if they occur, with few historical exceptions in some ancient dynasties in Egypt and Persia. But marriage with less close relatives, like uncle–niece, is accepted and even encouraged in a few cultures. The Judeo-Christian tradition strongly condemned incest and oscillated between avoidance and tolerance of less close consanguineous unions. First-cousin marriages are extremely common, ranging between 20 and 50% of all marriages in Moslem...

  15. Bibliography
    (pp. 303-312)
  16. Index
    (pp. 313-316)
  17. Back Matter
    (pp. 317-318)