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PubMed1997

Nonrandom mating in pikas Ochotona princeps: evidence for inbreeding between individuals of intermediate relatedness.

The extent and effect of inbreeding in natural populations remain largely undetermined. Pikas Ochotona princeps have been considered a likely candidate for close inbreeding in natural populations due to observations of frequent juvenile philopatry (colonization of natal home range or neighbouring home range) and high levels of spatial overlap and social tolerance between neighbouring individuals of the opposite sex. A 4-year investigation of inbreeding in pikas, however, has revealed that dispersal and mating patterns are uncoupled in this species, i.e. explained by different hypotheses. DNA fingerprinting analysis revealed that band-sharing scores between mated pairs, identified via parentage analysis, were not commensurate with band-sharing among known first-order relatives, but were similar to scores for a small sample of known second-order relatives (i.e. half-siblings grandparent-grandchild pairs). Band-sharing scores between mated pairs were then compared with those between potential mated pairs within the population to assess whether mating was random or nonrandom with respect to genetic similarity. The results of Monte Carlo randomization tests show that pikas mated with individuals with intermediate genetic similarity in greater proportion than would be expected by chance. These data suggest mate choice in pikas may be based upon intermediate levels of relatedness.

Animals↗
PubMed1989

Inbreeding effects on fetal growth in Beirut, Lebanon.

Effects of consanguineous marriages on offspring's gestational age and anthropometrics at birth were investigated in Beirut through a hospital-based survey of 1,252 newborns. Twenty-five percent of all newborns were inbred, and the mean inbreeding coefficient was 1.25%. Neither prematurity rate nor weight, length, head circumference, and chest circumference (considered individually, or as a whole) showed a significant pattern by type of parental consanguinity. Failure to demonstrate significant inbreeding effects is reported in several other studies and generally interpreted as the long-term result of continued inbreeding practices.

Anthropometry↗
PubMed2005

Inbreeding levels and consanguinity structure in the Basque province of Guipúzcoa (1862-1980).

This work analyzes the spatial heterogeneity of consanguinity in the Basque province of Guipúzcoa (Spain), using data provided by Catholic dispensations (1862-1980). Secular trends in consanguinity rates (%M(C)) and mean inbreeding coefficient (F) were similar in the seven Guipúzcoan regions considered, with peaks between 1881-1920 and subsequently a gradual decline. Substantial differences in consanguinity characteristics emerged when the regions were classified according to level of urbanization. Principal component analysis (accounting for more than 85% of the total variance in consanguinity variables) clearly discriminated between urbanized and less urbanized regions. The latter stand out for their high consanguinity rates (3.57-6.73%), mean inbreeding coefficient (0.00112-0.00240), and M22/M33 ratio (M22, first cousins; M33, second cousins), which ranged between 0.89-1.48. Moreover, in less urbanized regions, marital consanguinity was eminently local, and mainly conditioned by regional endogamy (71.4-85.0%). By contrast, urban subpopulations showed the lowest consanguinity rates (1.60-1.96%) and mean inbreeding coefficient (around 0.0007). In these regions, the M22/M33 ratio also exhibited high values (1.07-1.56), but this time at the expense of the contribution of the immigrant group. Discussion of the factors that could have modeled this spatial variation in consanguinity centers on: 1) demographic aspects related to the chronology and intensity of industrialization, 2) the geography of the territory and the geography of peopling, and 3) linguistic differences, expressed in the uneven distribution of Basque-speakers among the different territories considered.

Consanguinity↗
PubMed2002

Properties of the transmission-disequilibrium test in the presence of inbreeding.

Family-based association tests such as the transmission-disequilibrium test (TDT), which compare alleles transmitted and non-transmitted from parents to affected offspring, are widely used to detect the role of genetic risk factors in diseases. These methods have the advantage of being robust to population stratification and are thus believed to be valid whatever the population context. In different studies of the statistical properties of the TDT, parents of affected offspring are typically assumed to be neither inbred nor related. In many human populations, however, this assumption is false and parental alleles are then no longer independent. It is thus of interest to determine whether the TDT is a valid test of linkage and association in the presence of inbreeding. We present a method to derive the expected value of the TDT statistic under different disease models and for any relationship between the parents of affected offspring. Using this method, we show that in the presence of inbreeding, the TDT is still a valid test for linkage but not for association. The power of the test to detect linkage may, however, be increased in the presence of inbreeding under different modes of inheritance.

Consanguinity↗
PubMed2000

Evolution of seed dormancy due to sib competition: effect of dispersal and inbreeding.

The effect of dispersal and inbreeding on the evolution of seed dormancy to avoid sib competition is theoretically investigated, using a model which assumes a plant population with patchy spatial structure in a constant environment. Applying the inclusive fitness method, the evolutionarily stable dormancy rates are analytically derived for three cases: (a) an asexual haploid population, (b) a diploid-hermaphrodite population in which the dormancy rate is controlled by seeds, and (c) a diploid-hermaphrodite population in which the dormancy rate is controlled by mother plants. The evolutionarily stable dormancy rates decrease in the order of case (c), case (a), and case (b). In all the cases, the evolutionarily stable dormancy rates increase with decreasing the dispersal rate. Although inbreeding generally increases the evolutionarily stable dormancy rates, inbreeding due to selfing reduces the rate exceptionally in case (c).

Biological Evolution↗
PubMed1989

Inbreeding effects on average heterozygosity in the Sudan.

In the first series, the average heterozygosity based on ten polymorphic loci (Rhesus, MN, P, and Kell blood groups; haemoglobin; serum haptoglobin; transferrin; red cell acid phosphatase, phosphoglucomutase-1 and glyoxalase-1) was determined among the offspring of unrelated (n = 328) and related (first-cousin) matings (n = 466) in the Sudan. The estimated average heterozygosity was found to be the same in the offspring of the first-cousin and unrelated parents (0.3628 +/- 0.0584 and 0.3697 +/- 0.0581, respectively). In the second series, the average heterozygosity at five polymorphic loci (Rhesus blood group, haemoglobin, serum haptoglobin and transferrin and red cell acid phosphatase) was estimated in several tribes with variable levels of inbreeding coefficients. The estimated average heterozygosity varied from 0.14 +/- 0.09 to 0.37 +/- 0.08 in different tribes with varying degrees of inbreeding coefficients (alpha x 10(5) of 967-3,904). However there was no significant correlation between the level of parental inbreeding with either average heterozygosity or deviation from the Hardy-Weinberg equilibrium in the offspring.

Blood Group Antigens↗
PubMed2006

Modeling the effect of inbreeding among founders in linkage analysis.

In this paper, we present a unified mathematical model for linkage analysis that allows for inbreeding among founders in all families. The identical by descent (IBD) configuration of each pedigree is modeled as a Markov process containing two parameters; the inverse inbreeding and kinship coefficient and a rate parameter proportional to the inverse expected length of chromosome segments shared IBD by two different founder haplotypes. We use hidden Markov models and define a forward-backward algorithm for computing the conditional IBD-distribution given marker data, thereby extending the multipoint method of Lander and Green [1987. Construction of multilocus genetic maps in humans, Proc. Natl. Acad. Sci. USA 84, 2363-2367] to situations where founders are inbred. Our methodology is valid for arbitrary pedigree structures. Simulation and theoretical approximations for nonparametric linkage (NPL) analysis based on affected sib pairs reveal that NPL scores are inflated and type 1 errors increased when the inbreeding coefficient or rate parameter is underestimated. When the parents are genotyped, we present a general way of modifying the score function to drastically reduce this effect.

Algorithms↗
PubMed1994

Inbreeding in Ojeda and Pernia, 1875-1985, province of Palencia, Spain.

The degree of isolation was assessed in two contrasting regions in Northern Palencia, Spain, one mountainous with small villages in the valleys (Pernia), the other lower and more open (Ojeda), with corresponding differences in economy. Using data from the parish and diocesan records, the frequencies of consanguineous marriages were calculated from the dispensation data, and the evolution of inbreeding compared. The more isolated region shows a greater degree of inbreeding, though not as high as in some other parts of Spain. Both regions show a decline in inbreeding with time, though in neither did the results indicate that geographic isolation was very outstanding. The most frequent types of consanguineous unions occur between second cousins.

Consanguinity↗
PubMed2001

Estimates of cousin marriage and mean inbreeding in the United Kingdom from 'birth briefs'.

From 626 ascendant genealogies, known as 'birth briefs', deposited by members of the Society of Genealogists in their London library, rates of consanguineous marriage and coefficients of mean inbreeding (a) of offspring were estimated for cohorts of marriages contracted in the late nineteenth and early twentieth centuries. The rate of first cousin marriage in the generation estimated to have married during the 1920s was 0.32%, with no marriages between second cousins. The mean inbreeding coefficient for the offspring of these marriages was estimated as 0.0002. In the previous generation 1.12% of the marriages were between first cousins, and the estimate of mean inbreeding was 0.0007. Comparison with data taken from the published literature suggests that the levels of cousin marriage observed are consistent with a secular decline during the late nineteenth and twentieth centuries.

Birth Rate↗
PubMed1999

Factors influencing the extent of inbreeding depression: an example from scots pine

Detailed studies suggest that the level of inbreeding depression may vary between populations. In a study of Scots pine from Finland, the level of inbreeding depression was much lower in northern than in southern populations. We have examined theoretically whether population genetic factors, such as the level of selfing, intensity of selection against heterozygotes or homozygotes, level of mutation, a bottleneck, finite population size, or the level of polyembryony could account for this difference. Higher selfing or stronger selection against heterozygotes in the north, both at biologically reasonable levels, appear to produce changes consistent with the observed differences and we consider these to be the most likely explanations. In addition, the differences could have accumulated by these mechanisms over the age of the northern population, approximately 100 generations. Finally, the differences generated by these factors could still be maintained in the face of reasonable levels of gene flow from the south. Such a comprehensive theoretical investigation of this example has given some general insight into the potential influence of these evolutionary factors on the level of inbreeding depression and provides an approach that could be used to understand similar phenomena in other examples.

Journal Article↗
PubMed1977

The inbreeding coefficients of the Hadza.

A systematic tabulation is provided of the frequency of different types of inbreeding in the Hadza. Genealogical information was obtained for 931 individuals, alive and dead. Inbreeding was encountered with 165 individuals. There were 49 different types of inbred genealogy. No attempt was made to calculate an average inbreeding coefficient and the reasons for this are given in the text.

Consanguinity↗
PubMedDate not supplied

Matrimonial distance, inbreeding coefficient and population size: Dhangar data.

Data on the distance between the birthplaces of spouses (matrimonial distance) were collected from 2,260 married individuals belonging to 21 endogamous castes of the Dhangar (shepherd) cast-cluster of Maharashtra, India. The general form of the distribution of matrimonial distances is one which is extremely positively skewed and leptokurtic. The percentage of intra-village marriages generally decreases from the southern areas of Maharashtra to the northern areas of the state, as does the inbreeding coefficient. This situation is in conformity with the socio-cultural norms regulating matrimonial choice in south and north India. An attempt has been made to relate the degree of inbreeding to the mean matrimonial distance and population size. The mean matrimonial distance is more useful in predicting the degree of inbreeding than population size.

Consanguinity↗
PubMedDate not supplied

Genetic structure of the Azores: marriage and inbreeding in Flores.

Flores is one of the smallest and most westerly islands of the Atlantic archipelago of the Azores. This preliminary account of the population's demography and genetic structure uses dispensations to contract consanguineous marriages taken from the Roman Catholic marriage registers in order to estimate mean inbreeding rates in the population over the period 1860-1980. Comparisons are made with inbreeding rates on the Portuguese mainland and elsewhere in Western Europe, and reasons suggested to explain the rather high rates of inbreeding encountered on Flores.

Azores↗
PubMed1999

Dispersal and Inbreeding Avoidance.

Using a game-theoretical approach, we investigate the dispersal patterns expected if inbreeding avoidance were the only reason for dispersal. The evolutionary outcome is always complete philopatry by one sex. The rate of dispersal by the other sex depends on patch size and mating system, as well as inbreeding and dispersal costs. If such costs are sex independent, then two stable equilibria coexist (male or female philopatry), with symmetric domains of attraction. Which sex disperses is determined entirely by history, genetic drift, and gene flow. An asymmetry in costs makes one domain of attraction extend at the expense of the other. In such a case, the dispersing sex might also be, paradoxically, the one that incurs the higher dispersal costs. As asymmetry increases, one equilibrium eventually disappears, which may result in a sudden evolutionary shift in the identity of the dispersing sex. Our results underline the necessity to control for phylogenetic relationships (e.g., through the use of independent-comparisons methods) when investigating empirical trends in dispersal. Our model also makes quantitative predictions on the rate of dispersal by the dispersing sex and suggests that inbreeding avoidance may only rarely be the sole reason for dispersal.

evolutionarily stable strategy↗
PubMed1989

A FORTRAN subroutine to compute inbreeding and kinship coefficients according to the number of ancestral generations.

This paper presents a FORTRAN IV subroutine to calculate inbreeding and kinship coefficients from pedigree information in a diploid population without self-fertilization. The user can specify the number of ancestral generations to be taken into account. It is thus possible to determine contributions of succeeding ancestral generations to the inbreeding and kinship coefficients under consideration. The subroutine is based on a recursive procedure that generates systematically all paths connecting two individuals. NP and NM, whose kinship coefficient is to be calculated (or between the father NP and the mother NM of the individual whose inbreeding coefficient is to be calculated). These paths obey the following conditions: (i) a given path does not contain the same parent-offspring link more than once; (ii) the vertex of a path is an ancestor common to individuals NP and NM, with a rank lower or equal to the parameter specified in input. Constraints regarding the size of the corpus of genealogical data and the storage method are discussed, as well as the interest of this subroutine compared to the existing ones. An example of application is given.

Algorithms↗
PubMed1977

Inbreeding estimation from population data: models, procedures and implications.

Four different estimation procedures for models of population structure are compared. The parameters of the models are shown to be equivalent and, in most cases, easily expressed in terms of the parameters WRIGHT calls "F-statistics." We have estimated the parameters of each of these models with data on nine codominant allele pairs in 47 Yanomama villages, and we find that the different estimators for a given parameter all yield more or less equivalent results. F-statistics are often equated to inbreeding coefficients that are definid as the probability of identity by descent from alleles taken to be unique in some founding population. However, we are led to infer from computer simulation and general historical considerations that all estimates from genotype frequencies greatly underestimate the inbreeding coefficient for alleles in the founding population of American Indians in the western hemisphere. We surmise that in the highly subdivided tribal populations which prevailed until the recent advent of civilization, the probability of identity by descent for homologous alleles was roughly 0.5. We consider some consequences of working with the customary, much lower, estimates--0.005 to 0.01--if, on the time scale of human evolution, these represent only a very recent departure from the inbreeding intensity that prevailed before civilization.

Alleles↗
PubMed1979

The effects of inbreeding and of some genetic polymorphisms on blood pressures, pulse rate and hematocrit in Northeastern Brazil.

The possible role of genetic mechanisms, as revealed by inbreeding depression and pleiotropic effects of the ABO, Es D and CA II loci, on blood pressures, pulse rate and hematocrit, was studied in a sample of 7,642 migrant Brazilian individuals of rural origin. It was not possible to confirm previous claims of the effects of ABO blood groups system and inbreeding on diastolic blood pressure. On the other hand, a significant inbreeding depression on pulse rate of about 1.23 bmp/10% F, among adult individuals, was revealed. The observed significant effects of several markers on hemodynamic variables, due to its number, were attributed to chance.

Blood Pressure↗
PubMed1991

Inbreeding in Saguenay-Lac-St-Jean (Quebec, Canada): a study of Catholic Church dispensations 1842-1971.

Saguenay-Lac-St-Jean (SLSJ) is a rather geographically isolated region of Quebec which shows a high occurrence of hereditary disorders. It has been suggested that high inbreeding might explain this situation. We studied the inbreeding in the SLSJ region by 10-year periods from 1842 till 1971 using the Catholic Church dispensations. The values of the mean inbreeding coefficient were found to be low during the whole period, reaching a peak of 22.94 x 10(-4) during the period 1902-1911. The values observed in the SLSJ were lower than those found in most regions of Quebec and similar to those reported in European populations.

Catholicism↗