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PubMed2001

Overdominant epistatic loci are the primary genetic basis of inbreeding depression and heterosis in rice. II. Grain yield components.

The genetic basis underlying inbreeding depression and heterosis for three grain yield components of rice was investigated in five interrelated mapping populations using a complete RFLP linkage map, replicated phenotyping, and the mixed model approach. The populations included 254 F(10) recombinant inbred lines (RILs) derived from a cross between Lemont (japonica) and Teqing (indica), two backcross (BC) and two testcross populations derived from crosses between the RILs and the parents plus two testers (Zhong413 and IR64). For the yield components, the RILs showed significant inbreeding depression and hybrid breakdown, and the BC and testcross populations showed high levels of heterosis. The average performance of the BC or testcross hybrids was largely determined by heterosis. The inbreeding depression values of individual RILs were negatively associated with the heterosis measurements of the BC or testcross hybrids. We identified many epistatic QTL pairs and a few main-effect QTL responsible for >65% of the phenotypic variation of the yield components in each of the populations. Most epistasis occurred between complementary loci, suggesting that grain yield components were associated more with multilocus genotypes than with specific alleles at individual loci. Overdominance was also an important property of most loci associated with heterosis, particularly for panicles per plant and grains per panicle. Two independent groups of genes appeared to affect grain weight: one showing primarily nonadditive gene action explained 62.1% of the heterotic variation of the trait, and the other exhibiting only additive gene action accounted for 28.1% of the total trait variation of the F(1) mean values. We found no evidence suggesting that pseudo-overdominance from the repulsive linkage of completely or partially dominant QTL for yield components resulted in the overdominant QTL for grain yield. Pronounced overdominance resulting from epistasis expressed by multilocus genotypes appeared to explain the long-standing dilemma of how inbreeding depression could arise from overdominant genes.

Breeding↗
PubMed1987

An epidemiologic approach to the evaluation of the effect of inbreeding on prereproductive mortality.

Although many studies report deleterious effects of inbreeding on prereproductive mortality (death before age 20 years), such effects are usually measured in terms of genetic load, a concept much debated in the literature. To evaluate the public health impact of inbreeding on prereproductive mortality in terms of relative and attributable risks, the authors reviewed 31 studies with 294 observations comparing various stages of infant and child mortality in offspring of unrelated parents with offspring of first cousin, first cousin once removed, and second cousin marriages, respectively. Compared with offspring of unrelated parents, offspring of first cousin marriages have a higher risk of prereproductive mortality (median relative risk (RR) = 1.41, signed-rank test, p less than 0.01). Offspring of first cousin once removed and second cousin marriages had median relative risks of 1.16 and 1.26, respectively. Countries with relatively higher rates of consanguineous marriages (greater than 5%) had lower median relative risks than did countries with lower consanguinity rates. Also, the higher the mortality rate in the population, the lower the effect of consanguinity (median relative risk). Because of the rarity (less than 5%) and declining trends of consanguineous marriages in many places of the world, and because of their modest effect on prereproductive mortality (RR less than 2.0), it can be shown that the attributable risk of prereproductive mortality due to consanguineous marriages is less than 5%. Except for a few places with very high inbreeding levels, inbreeding has a minor impact on mortality in the prereproductive period.

Consanguinity↗
PubMed1977

The relationship between inbreeding, migration and population density in Norway.

An investigation of the present levels of inbreeding and the proportion of non-migrants (residents in municipality of birth) in rural districts of Norway reveals a relationship between these two characteristics. There is a steady upward trend from 0.39% first- and second-cousin marriages in municipalities with less than 50% non-migrants to 4.3% such consanguineous matings in municipalities where 85% or more of the inhabitants are non-migrants. There is also a significant negative correlation (rs=-0.86, N=18) between inbreeding and population density per square km by county in Norway. In rural districts of Norway maximum inbreeding is observed in sparsley populated areas with maximum proportion of non-migrants, and the ratio of second- to first-cousin marriages ranges between 3.4 and 4.1. A similar high ratio (3.7) is also encountered in densely populated trading and industrial municipalities and in the smaller towns, whereas the semi-urban municipalities and the larger towns have the lowest inbreeding recorded and also a low ratio (1.9). The lowest proportion of non-migrants (39.3%) is recorded in the semi-urban municipalities.

Consanguinity↗
PubMed1980

Inbreeding in a Brazilian general hospital.

A group of 925 adult in-patients of a Brazilian general hospital was matched by race (subdivided in five groups) and age with a group of 925 of their visitors, who were taken as controls. Illiteracy increases from Whites to Blacks and is significantly more prevalent among the patients than among their respective controls. Inbreeding, on the contrary, increases from Blacks to Whites. White patients showed a significantly higher rate of inbreeding than their corresponding controls. The difference is also significant for the fraction Whites plus Light Mulattoes, but not for the other race subgroups. As regards the total, the significance is present only in a one-tailed distribution. It is concluded that the inbreeding load (if any) acting on the total of the patients is negligible; it seems significantly different from 0 only among Whites. No inbreeding effect could be verified, however, on any particular condition among the Whites. Estimates of the number of morbid equivalents per gamete (morbons) revealed values which are both significantly (among Whites and Whites plus Light Mulattoes) and non-significantly (among the other racial subgroups) different from zero. These estimates reflect the situation in the sample which has been artificially organized to contain 50% of patients.

Adult↗
PubMed1996

Genetic referrals of Middle Eastern origin in a western city: inbreeding and disease profile.

Inbreeding or consanguineous marriage is a common traditional practice in Middle Eastern cultures. Studies from various countries and communities of this region showed that the frequencies range from 20% to greater than 70%. Inbreeding is known to have adverse effects on morbidity and mortality, in particular with respect to autosomal recessive disorders. This study examined 200 couples representing all referrals of Middle Eastern origin seen at a large Clinical Genetics Unit in Montreal. They were compared with a similar sized group of different cultural backgrounds from among the same referrals. The rate of intercultural marriages and inbreeding was found to be 24% and 23.5% respectively in the Middle Eastern group, while they were 22.5% and 5% in the comparison group. Excluding the referrals for consanguinity only, the rate of inbreeding among the study group was 16.4%. Within the Middle Eastern group, autosomal recessive disorders were more than twice as common in the inbred than in the non-inbred families, the pattern of which is consistent with previous observations.

Chromosome Aberrations↗
PubMed2001

Towards a complete North American Anabaptist Genealogy II: analysis of inbreeding.

We describe a large genealogy data base, which can be searched by computer, of 295,095 Amish and Mennonite individuals. The data base was constructed by merging our existing Anabaptist Genealogy Database 2.0 containing approximately 85,000 individuals with a genealogy file containing approximately 242,000 individuals, kindly provided by Mr. James Hostetler. The merging process corrected thousands of inconsistencies and eliminated hundreds of duplicate individuals. Geneticists have long been interested in Anabaptist populations because they are closed and have detailed written genealogies. The creation of an enlarged and unified data base affords the opportunity to examine inbreeding trends and correlates in these populations. We show the following results. The frequency of consanguineous marriages shows steady increase over time and reached approximately 85% for individuals born in 1940-1959. Among consanguineous marriages, the median kinship coefficient stayed stable in the 19th century, but rose from 0.0115 to 0.0151 in the 20th century. There are statistically significant associations (p < 0.0001) between inbreeding and family size and interbirth intervals in the 20th century. There is an association (p < 0.0005) between inbreeding and early death for individuals born in 1920-1959. However, this association reverses dramatically (p < 0.0005 in the opposite direction) for individuals born in 1960-1979. We tested for an association between inbreeding and being the mother of twins, but found none.

Birth Intervals↗
PubMed2005

A threefold genetic allee effect: population size affects cross-compatibility, inbreeding depression and drift load in the self-incompatible Ranunculus reptans.

A decline in population size can lead to the loss of allelic variation, increased inbreeding, and the accumulation of genetic load through drift. We estimated the fitness consequences of these processes in offspring of controlled within-population crosses from 13 populations of the self-incompatible, clonal plant Ranunculus reptans. We used allozyme allelic richness as a proxy for long-term population size, which was positively correlated with current population size. Crosses between plants of smaller populations were less likely to be compatible. Inbreeding load, assessed as the slope of the relationship between offspring performance and parental kinship coefficients, was not related to population size, suggesting that deleterious mutations had not been purged from small populations. Offspring from smaller populations were on average more inbred, so inbreeding depression in clonal fitness was higher in small populations. We estimated variation in drift load from the mean fitness of outbred offspring and found enhanced drift load affecting female fertility within small populations. We conclude that self-incompatibility systems do not necessarily prevent small populations from suffering from inbreeding depression and drift load and may exacerbate the challenge of finding suitable mates.

Alleles↗
PubMed2000

Trends in inbreeding, isonymy, and repeated pairs of surnames in the Valserine Valley, French Jura, 1763-1972.

The estimates of inbreeding derived from pedigrees and frequency of isonymous marriages (i.e., between persons of the same surname) are compared using genealogical and isonymic information from 4,899 marriages recorded between 1763 and 1972 in 4 rural villages of the French Jura region (a mountainous area near the Swiss border). Before the second half of the 20th century, the two kinds of estimates show a different temporal evolution. The mean inbreeding coefficient based on pedigrees increases between 1763 and 1852 and reaches a maximum between 1853 and 1882 (alpha = 0.0028), with a very low percentage (< 1%) the result of remote kinship. The mean inbreeding coefficient based on isonymy is always higher, with a maximum observed between 1793 and 1822 (F = 0.0200), and it remains roughly the same between 1763 and 1882 (F = 0.0150), with a high percentage resulting from a random component (Fr), a consequence of the small population size and genetic drift. After 1883, the 2 mean coefficients decrease. This discordance is largely explained by the poor quality, for the first periods, of the genealogical data base, which ignores the more remote links of kinship, justifying the use of the model of Crow and Mange (1965) to explore consanguinity during the more ancient periods. The temporal evolution of the repeated pairs of surnames index (RP) confirms the recent evolution of the marital structure of the valley. Moreover, it appears that isonymous marriages and repeated and unique pairs of surnames constitute 3 distinct matrimonial groups characterized by both a different mean coefficient of inbreeding (alpha) and a different rate of endogamy.

Consanguinity↗
PubMed1992

Inbreeding effects on reproductive outcome: a study based on a large sample from the endogamous Vadde of Kolleru Lake, Andhra Pradesh, India.

Inbreeding effects on reproductive outcome vis-à-vis fertility, prenatal loss and prereproductive mortality, and secondary sex ratio of live and dead children were examined in a large sample of 2078 women of the Vadde fishing population of Kolleru Lake in Andhra Pradesh, India. Demographically, this population is a single endogamous unit. By using an exponential regression model with the proportion of offspring survival as a dependent variable and the inbreeding coefficient as an independent variable, I further examined the inbreeding effects. The results were compared with results from other fishing groups and other southern Indian and non-Indian populations. The results among the Vadde were consistent with those found for other groups of Telugu-speaking fishermen and several other southern Indian populations in that the effects were neither perceptible nor significant. The average B value and the number of lethal equivalents found for the highly inbred southern Indian populations in general and for the Vadde in particular were much smaller than those from other parts of the world, providing empirical support to Sanghvi's hypothesis on long-term effects of inbreeding.

Adolescent↗
PubMed1990

Inbreeding as measured by isonymy in two Venezuelan populations and its relationship to other variables.

Isonymy is a useful approach to the study of population structure and thus can be utilized to detect deviations from random mating. In this study we give the results of an analysis of inbreeding levels and relate such variables as mean marital distance, surnames repeated in isonymous couples, and percentage of people using only maternal surnames to inbreeding and endogamy in two Venezuelan populations of black ancestry, Birongo and La Sabana. These populations differ in their sociocultural development and degree of isolation. We estimated inbreeding through isonymy and directly from genealogy. The most important findings are that the Ft values are higher than the a's, that the Fn component of Ft is higher than the Fr component, and that there is higher endogamy, inbreeding, and isolation in Birongo than in La Sabana. These results are in agreement with the sociocultural and historical background and development of each population. Nevertheless, both populations show similar temporal trends in almost all the variables analyzed. The use of isonymy as a complementary tool to study population structure is proposed, especially for Ibero-American populations.

Consanguinity↗
PubMed1996

Inbreeding patterns in the Gredos Mountain Range (Spain).

The relationships among the frequency of consanguineous marriages, inbreeding coefficient, period, village size, and altitude are analyzed for three rural valleys belonging to the Sierra de Gredos (central Spain). These valleys occupy an area of about 30 x 80 km2, and the average total number of inhabitants for the period 1877-1970 was 58,621. Information about a sample of 23,744 weddings celebrated between 1875 and 1974 was obtained from 48 village parish registers. The mean inbreeding level up to second cousins for the whole area was 0.0012. A high percentage of inbreeding variation (83%) can be explained by each village's census size, resulting in a different interslope consanguinity pattern consisting of higher inbreeding levels in most northern localities in the Gredos mountains. This north-south geographic trend is consistent with results on blood polymorphisms from the same area (Mesa et al. 1994).

Altitude↗
PubMed1982

Inbreeding in three captive groups of rhesus monkeys.

Using electrophoretic and serological genetic markers each of 17 potentially inbred matings in three groups of rhesus monkeys could be classified as either inbred or noninbred matings. Although nine of these 17 matings involved either father-daughter or paternal half-sib matings, only 7.4 were expected by chance alone. At least two, and possibly as many as three, of the nine cases of inbreeding involved father-daughter matings. Thus, no evidence of avoidance of inbreeding was observed in the closed captive groups of rhesus monkeys studied. Colony management policies must be developed to minimize the opportunity for or the deleterious effects of both father-daughter and half-sib matings. Furthermore, kin selection theory should consider why kin recognition, if it occurs, does not lead to avoidance of inbreeding.

Animals↗
PubMed1983

Inbreeding effects on dental morphometrics in Papio hamadryas.

The dentition of nonhuman primates (Papio hamadryas) was utilized to investigate the hypothesis that inbreeding will affect mean tooth size and shape. More than five hundred dental casts were collected from baboons at the Institute of Experimental Pathology and Therapy in Sukhumi, USSR. In addition, inbreeding coefficients for each monkey were obtained from pedigree records, some going back seven to nine generations. Each tooth was measured and scored for the presence of discrete morphological structures. Inbred and outbred groups were differentiated and divided by sex. Statistical analysis shows that for the most part inbred monkeys exhibit larger teeth than outbred monkeys, in both male and female groups. When the tooth area of inbreds was compared to that of outbreds, the differences were significant. However, there were no significant differences in frequency of discrete traits. Therefore, it can be concluded that primate dentition is affected by inbreeding, although dental metrics is a more sensitive indicator than morphology.

Animals↗
PubMed2005

Joint effect of selection, linkage and partial inbreeding on additive genetic variance in an infinite population.

Under the inifinitesimal model of gene effects, selection reduces the additive genetic variance by inducing negative linkage disequilibrium among selected genes. If the selected genes are linked, the decay of linkage disequilibrium is delayed, and the reduction of additive genetic variance is enhanced. Inbreeding in an infinite population also alters the additive genetic variance through the generation of positive association among genes within a locus. In the present study, the joint effect of selection, linkage and partial inbreeding (partial selfing or partial full-sib mating) on the additive genetic variance was modeled. The recurrence relations of the additive genetic variance between successive generations and the prediction equation of the asymptotic additive genetic variance were derived. Numerical computation showed that although partially inbred populations initially maintain larger genetic variances, the accumulated effect of selection overrides the effect of inbreeding. Stochastic simulation was carried out to check the precision of prediction, showing that the obtained equations give a satisfactory prediction during initial generations. However, the predicted values always overestimate the simulated values, especially in later generations. Based on these results, possible extensions and perspectives of the assumed model were discussed.

Animals↗
PubMed1992

The relationship between homozygosity level and animal physiology: iron content of plasma and whole blood as well as total iron binding capacity by transferrin (TIBC) in rats of various inbreeding coefficient.

Male and female wild Norway rats (Rattus norvegicus Erxleben) and male and female albino outbred rats (Ipf:RIZ) were crossbred. These animals were the control, noninbred group (0% inbred). By systematic full-sib mating, two experimental groups (50 and 91% of inbred) were raised. Half of each group (both males and females) was exposed to physical stress (3 days of starvation and 3 hr of swimming). The other half of each group was ether anesthetized to collect blood. The iron content of plasma and whole blood, as well as the total iron binding capacity, was determined by the Atom-Spec method. A significant decrease in the iron content of plasma and whole blood as well as the TIBC was observed by an increase in the inbreeding coefficient. Stress significantly influenced the iron content of plasma and whole blood as well as the TIBC, whereas the sex of the rats affected the whole-blood iron concentration and TIBC. Moreover, some double interactions had an impact on the iron content and TIBC. The interactions were as follows: plasma--inbreeding level and stress; whole blood--sex and stress; and TIBC--inbreeding level and sex.

Animals↗
PubMed2005

Selfing and inbreeding depression in seeds and seedlings of Neobalanocarpus heimii (Dipterocarpaceae).

We evaluated the degree of selfing and inbreeding depression at the seed and seedling stages of a threatened tropical canopy tree, Neobalanocarpus heimii, using microsatellite markers. Selection resulted in an overall decrease in the level of surviving selfed progeny from seeds to established seedlings, indicating inbreeding depression during seedling establishment. Mean seed mass of selfed progeny was lower than that of outcrossed progeny. Since the smaller seeds suffered a fitness disadvantage at germination in N. heimii, the reduced seed mass of selfed progeny would be one of the determinants of the observed inbreeding depression during seedling establishment. High selfing rates in some mother trees could be attributed to low local densities of reproductive individuals, thus maintenance of a sufficiently high density of mature N. heimii should facilitate regeneration and conservation of the species.

Ericales↗
PubMed1983

Variance of actual inbreeding.

The variances of actual inbreeding and coancestry in terms of their corresponding identities by descent were studied for finite populations. For inbreeding at a single locus, the total variance sigma 2 equal F(1-F) (F is the inbreeding coefficient) is comprised of a component sigma 2w within populations and a component sigma 2b between replicate populations. These variances increase in time to a maximum at about 1.1Ne generations for sigma 2w, about 2.3Ne generations for sigma 2b, and about 1.4 NE generations for sigma 2, and decrease thereafter (Ne is effective population size). The ratio sigma 2b/sigma 2 is ever increasing to an asymptote in the range 0.4-0.5 depending on Ne and the mating system. For finite populations with variation in pedigree F's, there are contributions sigma 2wF within and sigma 2bF between populations. The component sigma 2bF is insignificant except for very small populations, and sigma 2wF is largest in the early generations and then decreases roughly as (1-F)2/KNe where K is formulated in terms of the mating strategy and the degree of avoidance of mating relatives. An additional degree of avoidance increases K by a factor of 4. In a large population at equilibrium with respect to mixed self and random mating, sigma 2wF accounts for one-half to two-thirds of sigma 2w. Bringing in more loci leads to decomposition of the total variance into four components whose values are affected by linkages among the loci. The relationships between these components and sigma 2w, sigma 2wF, and sigma 2bF are elaborated in terms of tight and loose linkage. The exact computations of sigma 2wF and sigma 2bF require the use of two locus descent measures without linkage. The variances of various averages of actual identities by descent, such as the proportions for individuals or populations, are formulated for a sample of individuals.

Analysis of Variance↗
PubMed2004

Genetic analysis of inbreeding of two strains of the parasitic nematode Haemonchus contortus.

Haemonchus contortus is a sheep parasitic nematode that causes severe economic losses. Previous studies have indicated a high degree of genetic heterogeneity, which is hardly affected by selection for drug resistance. As a tool for the analysis of the population dynamics of H. contortus and its response to drug resistance, we designed a strategy to study the inbreeding of a benzimidazole-sensitive and a benzimidazole-resistant strain. After 15 generations, a theoretical inbreeding coefficient of 0.87 was achieved. The different stages of inbreeding were analysed using restriction fragment polymorphism, microsatellite variability and amplified fragment length polymorphism. Model-based clustering of the amplified fragment length polymorphism genotypes showed that the allele frequencies of the benzimidazole-resistant strain were stable during the last eight generations. In the sensitive strain a gradual shift of allele frequencies was observed, which led to a temporary increase of the genetic diversity around the eight generations.

Animals↗