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PubMed2003

Viability selection at three early life stages of the tropical tree, Platypodium elegans (Fabaceae, Papilionoideae).

Given the enormous number and high mortality of fertilized ovules in plants, it is possible that selection during the earliest stages of the life cycle plays an important role in shaping the genetic composition of plant populations. Previous research involving selection component analyses found strong evidence for viability selection in annual plant species. Yet despite this evidence, few attempts have been made to identify the magnitude and timing of viability selection as well as the mechanisms responsible for mortality among genotypes. Platypodium elegans, a Neotropical tree with high rates of early fruit mortality, represents an opportunity to study viability selection at a level of discernment not previously possible. Microsatellite markers were used to analyze the genetic composition of aborted embryos, as well as mature seeds and seedlings of the same cohort. While selection resulted in an overall decrease in self-fertilized progeny across each life stage, the greatest change in the genetic composition of progeny occurred between mature seeds and established seedlings. This suggested that inbreeding depression, and not late-acting self-incompatibility, was responsible for early selection. An investigation of the mature seed stage revealed that self-fertilized seeds weigh significantly less than outcrossed seeds. The result of this early selection conceals the mixed-mating system and high levels of inbreeding depression in Platypodium elegans, resulting in an apparently outcrossed adult population that does not differ significantly from Hardy-Weinberg expectations.

Alleles↗
PubMed2004

Epistasis and the temporal change in the additive variance-covariance matrix induced by drift.

The effect of population bottlenecks on the components of the genetic covariance generated by two neutral independent epistatic loci has been studied theoretically (additive, covA; dominance, covD; additive-by-additive, covAA; additive-by-dominance, covAD; and dominance-by-dominance, covDD). The additive-by-additive model and a more general model covering all possible types of marginal gene action at the single-locus level (additive/dominance epistatic model) were considered. The covariance components in an infinitely large panmictic population (ancestral components) were compared with their expected values at equilibrium over replicates randomly derived from the base population, after t consecutive bottlenecks of equal size N (derived components). Formulae were obtained in terms of the allele frequencies and effects at each locus, the corresponding epistatic effects and the inbreeding coefficient Ft. These expressions show that the contribution of nonadditive loci to the derived additive covariance (covAt) does not linearly decrease with inbreeding, as in the pure additive case, and may initially increase or even change sign in specific situations. Numerical examples were also analyzed, restricted for simplicity to the case of all covariance components being positive. For additive-by-additive epistasis, the condition covAt > covA only holds for high frequencies of the allele decreasing the metric traits at each locus (negative allele) if epistasis is weak, or for intermediate allele frequencies if it is strong. For the additive/dominance epistatic model, however, covAt > covA applies for low frequencies of the negative alleles at one or both loci and mild epistasis, but this result can be progressively extended to intermediate frequencies as epistasis becomes stronger. Without epistasis the same qualitative results were found, indicating that marginal dominance induced by epistasis can be considered as the primary cause of an increase of the additive covariance after bottlenecks. For all models, the magnitude of the ratio covAt/covA was inversely related to N and t.

Analysis of Variance↗
PubMed1994

Genetic variation of the St. Lawrence beluga whale population assessed by DNA fingerprinting.

Recent surveys suggest that the endangered St. Lawrence beluga (Delphinapterus leucas) population is not recovering significantly despite 20 years of protection. Dead individuals that have been autopsied show high levels of tumours and infections. This situation could be a result of pollution, loss of genetic variation, inbreeding depression or a combination of these factors. Analyses of DNA fingerprints from St. Lawrence belugas with three minisatellite probes (Jeffreys 33.6, 33.15 and M13) indicate a reduced level of genetic variation compared to Beaufort Sea animals. The average band-sharing between individuals of the St. Lawrence beluga population for the three probes (0.534, 0.573 and 0.478, respectively) was significantly higher than that of the Beaufort Sea beluga population (0.343, 0.424, 0.314, respectively). Higher levels of mean allele frequency in the St. Lawrence belugas (0.33 vs. 0.21) suggest that this population is composed of individuals which are related. Inbreeding depression could therefore be a factor in the lack of recovery of the St. Lawrence beluga population.

Alleles↗
PubMed1995

Natal dispersal and genetic structure in a population of the European wild rabbit (Oryctolagus cuniculus).

A combination of behavioural observation, DNA fingerprinting, and allozyme analysis were used to examine natal dispersal in a wild rabbit population. Rabbits lived in territorial, warren based social groups. Over a 6-year period, significantly more male than female rabbits moved to a new social group before the start of their first breeding season. This pattern of female philopatry and male dispersal was reflected in the genetic structure of the population. DNA fingerprint band-sharing coefficients were significantly higher for females within the same group than for females between groups, while this was not the case for males. Wright's inbreeding coefficients were calculated from fingerprint band-sharing values and compared to those obtained from allozyme data. There was little correlation between the relative magnitudes of the F-statistics calculated using the two techniques for comparisons between different social groups. In contrast, two alternative methods for calculating FST from DNA fingerprints gave reasonably concordant values although those based on band-sharing were consistently lower than those calculated by an 'allele' frequency approach. A negative FIS value was obtained from allozyme data. Such excess heterozygosity within social groups is expected even under random mating given the social structure and sex-biased dispersal but it is argued that the possibility of behavioural avoidance of inbreeding should not be discounted in this species. Estimates of genetic differentiation obtained from allozyme and DNA fingerprint data agreed closely with reported estimates for the yellow-bellied marmot, a species with a very similar social structure to the European rabbit.

Analysis of Variance↗
PubMed2005

Mating system of the Eurasian badger, Meles meles, in a high density population.

Badgers are facultatively social, forming large groups at high density. Group-living appears to have high reproductive costs for females, and may lead to increased levels of inbreeding. The extent of female competition for reproduction has been estimated from field data, but knowledge of male reproductive success and the extent of extra-group paternity remains limited. Combining field data with genetic data (16 microsatellite loci), we studied the mating system of 10 badger social groups across 14 years in a high-density population. From 923 badgers, including 425 cubs, we were able to assign maternity to 307 cubs, with both parents assigned to 199 cubs (47%) with 80% confidence, and 14% with 95% confidence. Age had a significant effect on the probability of reproduction, seemingly as a result of a deficit of individuals aged two years and greater than eight years attaining parentage. We estimate that approximately 30% of the female population successfully reproduced in any given year, with a similar proportion of the male population gaining paternity across the same area. While it was known there was a cost to female reproduction in high density populations, it appears that males suffer similar, but not greater, costs. Roughly half of assigned paternity was attributed to extra-group males, the majority of which were from neighbouring social groups. Few successful matings occurred between individuals born in the same social group (22%). The high rate of extra-group mating, previously unquantified, may help reduce inbreeding, potentially making philopatry a less costly strategy.

Animals↗
PubMed2005

Microsatellite variation and structure of 28 populations of the common wetland plant, Lychnis flos-cuculi L., in a fragmented landscape.

Habitat fragmentation is known to cause genetic differentiation between small populations of rare species and decrease genetic variation within such populations. However, common species with recently fragmented populations have rarely been studied in this context. We investigated genetic variation and its relationship to population size and geographical isolation of populations of the common plant species, Lychnis flos-cuculi L., in fragmented fen grasslands. We analysed 467 plants from 28 L. flos-cuculi populations of different sizes (60 000-54 000 flowering individuals) in northeastern Switzerland using seven polymorphic microsatellite loci. Genetic differentiation between populations is small (F(ST) = 0.022; amova; P < 0.001), suggesting that gene flow among populations is still high or that habitat fragmentation is too recent to result in pronounced differentiation. Observed heterozygosity (H(O) = 0.44) significantly deviates from Hardy-Weinberg equilibrium, and within-population inbreeding coefficient F(IS) is high (0.30-0.59), indicating a mixed mating breeding system with substantial inbreeding in L. flos-cuculi. Gene diversity is the only measure of genetic variation which decreased with decreasing population size (R = 0.42; P < 0.05). While our results do not indicate pronounced effects of habitat fragmentation on genetic variation in the still common L. flos-cuculi, the lower gene diversity of smaller populations suggests that the species is not entirely unaffected.

Altitude↗
PubMed2005

Invasion success and genetic diversity of introduced populations of guppies Poecilia reticulata in Australia.

High genetic diversity is thought to characterize successful invasive species, as the potential to adapt to new environments is enhanced and inbreeding is reduced. In the last century, guppies, Poecilia reticulata, repeatedly invaded streams in Australia and elsewhere. Quantitative genetic studies of one Australian guppy population have demonstrated high additive genetic variation for autosomal and Y-linked morphological traits. The combination of colonization success, high heritability of morphological traits, and the possibility of multiple introductions to Australia raised the prediction that neutral genetic diversity is high in introduced populations of guppies. In this study we examine genetic diversity at nine microsatellite and one mitochondrial locus for seven Australian populations. We used mtDNA haplotypes from the natural range of guppies and from domesticated varieties to identify source populations. There were a minimum of two introductions, but there was no haplotype diversity within Australian populations, suggesting a founder effect. This was supported by microsatellite markers, as allelic diversity and heterozygosity were severely reduced compared to one wild source population, and evidence of recent bottlenecks was found. Between Australian populations little differentiation of microsatellite allele frequencies was detected, suggesting that population admixture has occurred historically, perhaps due to male-biased gene flow followed by bottlenecks. Thus success of invasion of Australia and high additive genetic variance in Australian guppies are not associated with high levels of diversity at molecular loci. This finding is consistent with the release of additive genetic variation by dominance and epistasis following inbreeding, and with disruptive and negative frequency-dependent selection on fitness traits.

Animals↗
PubMed1975

Frequency of phenylketonuria in Norway.

By January 1973, a total of 146 homozygotes (born between 1875 and 1972) for phenylketonuria (PKU) had been identified in Norway. This is an incomplete total, particularly in respect of PKU cases born before 1950, because of the PKU mortality rate. Between 1951 and 1972, the observed incidence of PKU was unchanged at 0.07 plus and minus 0.01 per 1000 live births. Haematological screening of about one-third of all births in Norway between 1966 and 1972 indicated an incidence of 0.07 plus and minus 0.02 per 1000 liveborn screened. As expected, this was well below the observed incidence of 0.11 plus and minus 0.01 per 1000 from screening data from Denmark, and considerably higher than the observed value of 0.03 plus and minus 0.01 per 1000 screened in Sweden. In comparison, indirect estimates, using the inbreeding coefficent of parents of PKUs and that of the general population in Norway in the corresponding years (1874-1972), suggested a fall in incidence of PKU in Norway from 0.14 plus and minus 0.15 per 1000 live births in 1918, to 0.08 plus and minus 0.08 per 1000 in 1941, and to 0.06 plus and minus 0.06 per 1000 live births in 1972. The present level of inbreeding in Norway (obtained from the Medical Registration of Bith) is discussed and compared with information in the 1891 census, with the parish registers between 1889and 1902, and with the parochial lists for the years 1903-1941.

Adolescent↗
PubMed1976

Cerebellar ataxia and hypergonadotropic hypogonadism in two kindreds. Chance concurrence, pleiotropism or linkage?

Two kindreds with Marinesco-Sjögren's syndrome in three sibships are described. In five of the six affected, but in none of the unaffected sibs, a hypergonadotropic hypogonadism was observed. In one of the kindreds a high degree of inbreeding was revealed, and inbreeding likely also existed in the other kindred. The two families were not related. Marinesco-Sjögren's syndrome is known to be a distinct clinical entity, governed by autosomal recessive inheritance, and this also applies to hypergonadotropic hypogonadism. Several heredo-degenerative nervous disorders are accompanied by a hypogonadotropic hypogonadism, which is believed to be secondary to the neurological disorder, as in traumatic paraplegia. A hypergonadotropic hypoganadism cannot readily be explained in this way. We consider genetic linkage between two independent disorders as the most likely explanation for the observed concurrence.

Adolescent↗
PubMed1988

Neonatal screening for amino acidaemias in Karnataka, south India.

Consanguineous marriages are strongly favoured among the peoples of South India. Because of the potential genetic risks resulting from inbreeding, a neonatal screening project was established in 1980 in the state of Karnataka for the identification of amino acidaemias. To date, blood samples obtained by toe-stab from 98,256 neonates have been tested by thin layer chromatography, with 46 single and 70 general amino acidaemias detected. The coefficients of inbreeding (F) for the two groups of neonates were 0.0336 and 0.0350, by comparison with a previously determined F value for the general, new-born population of 0.0298. The most common single abnormality detected was tyrosinaemia, with spontaneous resolution in the majority of cases.

Amino Acid Metabolism, Inborn Errors↗
PubMed1990

Consanguinity and the genetic control of Down syndrome.

Eighty-three infants and children with a professional diagnosis of Down syndrome were studied cytogenetically. The results showed that 81.9% of them were trisomy 21 and 18.1% were the 46/47 + G type of mosaic. All cases were distributed according to parental consanguinity. The results showed that 77.9%, 16.2% and 5.9% of the trisomy 21 cases, and 53.3%, 26.7% and 20.0% of the mosaic cases were from non-consanguineous, first-cousin and second-cousin marriages, respectively. By combining all the cases, these percentages were 73.5%, 18.1% and 8.4%, respectively. Considering the high rate of inbreeding in Iraq (inbreeding coefficient = 0.0225) and using various statistical comparisons, these results revealed the lack of evidence for genetical control of non-disjunction in man.

Adolescent↗
PubMed1993

Congenital malformations, reproductive wastage and consanguineous mating.

A study was undertaken in Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry, South India, to understand the relation between congenital developmental disorders and consanguinity and also reproductive wastage and consanguinity. Four hundred children with existing congenital developmental disorders were studied with regard to their consanguineous parentage and compared with 1,000 randomly selected patients attending the paediatric outpatient department. There was a significantly higher prevalence of consanguinity in the study group (p < 0.001) and greater frequency in rural areas. The common types of consanguineous marriages were between first cousins (50.6%) and uncle and niece (42.4%). Frequency of consanguinity was not significantly related to religion and caste. The mean coefficient of inbreeding was 0.056. Consanguinity had no significant effect on average pregnancy rate and reproductive wastage. The frequency of consanguinity was significantly higher especially with autosomal recessive disorders (p < 0.001), congenital heart diseases (p < 0.001), multiple malformations (p < 0.001), neurological malformations (p < 0.005), chromosomal disorders (p < 0.01), genitourinary disorders (p < 0.02) and mental retardation-developmental disorders (p < 0.02). These observations stress the need for communicating the deleterious effects of inbreeding to the public through regular health education.

Abortion, Spontaneous↗
PubMed2004

Heterosis studies for yield and its components in bread wheat over environments.

A set of diallel crosses involving 10 parents was made to have information on the extent of heterosis over mid-parent and better parent and inbreeding depression for yield and yield contributing characters under three different environments. Marked heterobeltiosis for grain yield and its important components were observed. For grain yield, 83 crosses showed significant positive heterobeltiosis in all the three sowing dates, however, twenty crosses showed significant consistent heterobeltiosis for grain yield per plant over all the three environments. The maximum heterobeltiosis for grain yield per plant observed was 50.94% (Raj 3765 x HD 2285), 121.08% (PBW 373 x HD 2329) and 93.96% (PBW 373 x HD 2329) under early, normal and late sowing conditions, respectively. Cross PBW 373 x HD 2329 in both early and normal plantings and cross Raj 3765 x HD 2285 under late planting were observed most heterotic for grain yield. The crosses showing heterosis for grain yield were not heterotic for all the characters. Heterosis for grain yield per spike followed by tillers per plant and 1000-grain weight was independently associated with heterosis for grain yield in early and normal plantings. However, heterosis for grain yield per spike, dwarf plant height and tillers per plant contributed maximum towards yield heterosis. Significant inbreeding depression was recorded frequently for yield and yield contributing traits, however, in a few traits it was observed significant negative indicated that F(2) was superior to F(1) considered desirable combination for trait(s). The study reveals good scope for commercial exploitation of heterosis as well as isolation of pure lines among the progenies of heterotic F(1) for improvement of yield levels in bread wheat.

Analysis of Variance↗
PubMed2006

Understanding the genetics of autoimmune disease: two loci that regulate late onset Addison's disease in Portuguese Water Dogs.

Addison's disease, an immune-mediated disorder caused by destruction of the adrenal glands, is a rare disorder of Western European populations. Studies indicate that the disorder is polygenic in nature, involving specific alleles of the CTLA-4, DRB1*04 and DQ, Cyp27B1, VDR and MIC-A and -B loci. A similar immune form of Addison's disease occurs in several breeds of domestic dog, with frequencies ranging from 1.5 to 9.0%. The high frequency of the disease in domestic dog breeds likely reflects the small number of founders associated with many breeds, subsequent inbreeding, and the frequent use of popular sires. The Portuguese Water Dog (PWD) is a significantly affected breed. An analysis of 11,384 PWDs surveyed between 1985 and 1996 suggests a breed-specific disease incidence of 1.5%. As with humans, the disease is typically of late onset. This study involves a genetic comparison of Addison's disease in the PWD to the analogous disease in humans. The study is facilitated by the existence of complete pedigrees and a relatively high degree of inbreeding among PWDs. The breed originated from 31 founders, with 10 animals responsible for 90% of the current gene pool. We describe, specifically, the identification of two disease-associated loci, on Canis familiaris (CFA) chromosomes CFA12 and 37, which are syntenic with the human DRB1 histocompatibility locus alleles HLA-DRB1*04 and DRB1*0301, and to a locus for immunosuppression syntenic with CTLA-4. Strong similarities exist therefore in the complex genetic background of Addison's disease in humans and in the PWD. With the completion of the canine and human genome sequence, the purebred dog is set to become an important comparative model for Addison's as well as other human immune disorders.

Addison Disease↗
PubMed1976

Infantile cystinosis in France: genetics, incidence, geographic distribution.

A national distribution of 66 French patients, from 49 sibships, has been studied. Segregation analysis, using the maximum likelihood method, was found to agree with the theoretical values expected in recessive autosomal inheritance. The birthplaces of these patients show an unequal geographic distribution of cystinosis, the incidence being higher in Western France. Compared with the total number of live births during the period 1959 to 1972, the minimum incidence of the condition in the province of Brittany is 1 per 25 909, and the gene frequency 0.0062. In the rest of France, the minimum incidence is 1 per 326,440 and the gene frequency 0.0018. Application of Dahlberg's formula gives a similar result. The mean inbreeding coefficient is 530 X 10(-5), a figure 23 times higher than the mean coefficient of France. An indirect test of inbreeding, the distance between parental birthplaces, was studied, first using the French administrative boundaries, second by using kilometers. This distance was constantly smaller for the parents of patients than for the parents of controls. Analysis of two erythrocyte polymorphisms (ABO and Rh) showed a large excess of group A patients when compared with overall French data. These findings are difficult to interpret on genetic grounds. The genetic reasons for the unequal geographic distribution of cystinosis in France are discussed.

ABO Blood-Group System↗
PubMed1989

Consanguinity related prenatal and postnatal mortality of the populations of seven Pakistani Punjab cities.

A retrospective study was conducted on prenatal and postnatal mortality among the populations of seven cities in the Pakistani province of Punjab. Consanguineous marriages were strongly favoured and the coefficients of inbreeding (F) for the present generation in each locality ranged from 0.0236 to 0.0286. There was a highly significant relationship between the degree of inbreeding and mortality, with most consanguinity related deaths reported in the neonatal, infantile, and childhood periods. The findings strongly suggest that consanguinity may play a major role in the high rates of postnatal mortality observed in Pakistani communities now resident in the United Kingdom.

Abortion, Spontaneous↗
PubMed1993

Genetic relatedness among rabbiteye blueberry (Vaccinium ashei) cultivars determined by DNA amplification using single primers of arbitrary sequence.

Most improved cultivars of commercially important hexaploid rabbiteye blueberry were developed from only four native selections collected from the wild; thus, many cultivars are closely related by lineage. The consanguinity among major cultivars is a potential problem, as the rabbiteye blueberries are highly self-incompatible natural outcrossers with potential inbreeding depression. We investigated the extent of genetic relatedness among 15 improved cultivars and four wild selections by the technique of random amplified polymorphic DNA, also referred to as arbitrarily primed polymerase chain reaction. Single decanucleotides of arbitrary sequence revealed polymorphism among cultivars and wild selections. Genetic distances were estimated based on the amount of band sharing. Cluster analysis of genetic distance estimates tended to group siblings with each other and with one or both parents. The average genetic distance between improved cultivars decreased relative to the four wild parental selections, which might indicate progression towards inbreeding. The significance of increased genetic relatedness among the improved cultivars of rabbiteye blueberry and the application of molecular methods in breeding and commercial cultivation is discussed.

Base Sequence↗
PubMed1995

Conservation genetics.

Inbreeding depression, accumulation and loss of deleterious mutations, loss of genetic variation in small populations, genetic adaptation to captivity and its effect on reintroduction success, and outbreeding depression are reviewed. The impact of genetic factors in endangerment and extinction has been underestimated in some recent publications. Inbreeding depression in wildlife and in the field has been clearly established, while its impact has been greatly underestimated. The size of populations where genetic factors become important is higher than previously recognized, as Ne/N ratios average 0.11. Purging effects have been overestimated as a mechanism for eliminating deleterious alleles in small populations. The impact of loss of genetic variation in increasing the susceptibility of populations to environmental stochasticity and catastrophes has generally been ignored. Consequently, extinctions are often attributed to "nongenetic" factors when these may have interacted with genetic factors to cause extinction.

Adaptation, Biological↗