Use of the integral parameter of dermatoglyphic differences for determining the type of zygosity of twins]

A method is described increasing the reliability of twin zygosity diagnosis in cases when the possibility of using a large number of mendelian markers is restricted. The method is based on the determination of generalized index of dermatoglyphic differences between members of twin pair for 18 characteris of finger and palm dermatoglyphics and on principles of multivariate genetic analysis, which is worked out to determine the degree of heritability of multifactorial character and to study the structure of hereditary predisposition to multifactorial diseases. The efficiency of the method with respect to determinating the type of twin zygosity is approximately equivalent to the efficiency of using 5--6 mendelian marker systems.     

Genes and environment

Many quantitative characters depend on the action of a large number of genes and environmental factors. The mode of inheritance of these characters is polygenic. The phenotypic variance of the character is the sum of the components, thus the genetic and the environmental variances (VP = VG + VE). The degree of genetic determination VG/VP and VE/VP are difficult to estimate in man. The heritability a related coefficient to VG/VP can be estimated from the degree of ressemblance between relatives. The heritability is the additive genetique variance as a proportion of the phenotypic variance. Polygenic threshold inheritance can account for the familial non mendelian distribution of multifactorial diseases.     

Assumption-free estimation of heritability from genome-wide identity-by-descent sharing between full siblings

The study of continuously varying, quantitative traits is important in evolutionary biology, agriculture, and medicine. Variation in such traits is attributable to many, possibly interacting, genes whose expression may be sensitive to the environment, which makes their dissection into underlying causative factors difficult. An important population parameter for quantitative traits is heritability, the proportion of total variance that is due to genetic factors. Response to artificial and natural selection and the degree of resemblance between relatives are all a function of this parameter. Following the classic paper by R. A. Fisher in 1918, the estimation of additive and dominance genetic variance and heritability in populations is based upon the expected proportion of genes shared between different types of relatives, and explicit, often controversial and untestable models of genetic and non-genetic causes of family resemblance. With genome-wide coverage of genetic markers it is now possible to estimate such parameters solely within families using the actual degree of identity-by-descent sharing between relatives. Using genome scans on 4,401 quasi-independent sib pairs of which 3,375 pairs had phenotypes, we estimated the heritability of height from empirical genome-wide identity-by-descent sharing, which varied from 0.374 to 0.617 (mean 0.498, standard deviation 0.036). The variance in identity-by-descent sharing per chromosome and per genome was consistent with theory. The maximum likelihood estimate of the heritability for height was 0.80 with no evidence for non-genetic causes of sib resemblance, consistent with results from independent twin and family studies but using an entirely separate source of information. Our application shows that it is feasible to estimate genetic variance solely from within-family segregation and provides an independent validation of previously untestable assumptions. Given sufficient data, our new paradigm will allow the estimation of genetic variation for disease susceptibility and quantitative traits that is free from confounding with non-genetic factors and will allow partitioning of genetic variation into additive and non-additive components.     

Inheritance of 18 quantitative dermatoglyphic traits based on factors in MZ and DZ twins

18 quantitative finger and palmar dermatoglyphic traits were analyzed with the aim of determining genetic effects and common familial environmental influences on a large (358 nuclear pedigrees) number of twins (MZ and DZ). Genetic analysis based on principal factors includes variance and bivariate variance decomposition analysis. Especially, Factor 1 (digital pattern size) is remarkable, due to its degree of universality. The results of genetic analysis revealed all three extracted factors have significant proportion of additive genetic variance (93.5% to 72.9%). The main results of bivariate variance decomposition analysis appears significant correlation in residual variance between digital pattern size factor (Factor 1) versus finger pattern intensity factor (Factor 4), and palmar main lines factor (Factor 2) verses a-b ridge count (Factor 3), but there was no significant correlation in the genetic variance of factors.     

Heritability of neurodynamics and psychodynamics in human populations

A component analysis of human neurodynamic and psychodynamic characters in the norm was carried out in 8 human populations characterized by different degrees of isolation and ethnic origin. An increase in phenotypic variability and a decrease in heritability with increasing complexity of organization of the characters under study were demonstrated for all these populations. The additive effect plays the major role in genetic determination of neurodynamic and psychodynamic characters studied. For a number of neurodynamic parameters the effect of intralocus dominance indicative of the oligogenic determination system was observed. Data in favour of real contribution of the factors linked to X-chromosome were obtained for simple sensomotor reactions.     

Heredity and the bimanual asymmetry of human finger and palm dermatoglyphs

An attempt has been made to study the effect of hereditary factors on the asymmetry of morpho-functional quantitative traits, in particular, finger and palm dermatoglyphs (24 indices). The results of examination of 140 twin pairs (83 monozygotic and 57 dizygotic) are presented. The hereditary effects have been found for ten traits when an account is taken of the asymmetry direction, and for nine traits when asymmetry direction is not considered.     

Dominance and environmental variances: their effect on heritabilities estimated from twin data

A method for partitioning genetic variance estimated from twin data into additive and dominance variances was presented using Falconer's variance component model. The effects of dominance and environmental variances on a number of heritability estimates were also reviewed. A heritability estimate, based on the analysis of variance and the genetic variance estimates presented by HASEMAN and ELSTON and CHRISTIAN et al. which utilizes all available information from twin data, was proposed and discussed. This estimate seems to be the least affected by fluctuations in the magnitudes of dominance and environmental variances.     

Sexual dimorphism in the Chuvashian population of Russia in two types of dermatoglyphic traits: principal component analysis

With the aim of determining sexual dimorphism in the component structures among the Chuvashian population of Russia, finger and palmar dermatoglyphics of 547 individuals (293 males, 254 females) were analyzed. The sex differences in two categories of dermatoglyphic traits (22 quantitative traits and 38 asymmetry and diversity traits) are reflected differently and contradictory with other ethnic groups. However, a common feature of the factor 1 "digital pattern size factor" (finger ridge counts from the first category of traits) indicate its degree of universality when compared with other populations, which suggests that the variability of finger ridge counts is determined by the same genes that control the pattern types. The factors "intra-individual finger diversity factor", and "bi-lateral asymmetry factor" extracted from the second category of dermatoglyphic traits are also similar in both sexes. However, these components are hardly described in the literature. The nature of variation of these components (from two categories of dermatoglyphic traits) appears with a good similarity between sexes, which suggests their common biological validity of the underlying component structures of the finger and palmar dermatoglyphic characters.     

Estimates of genetic variance in an F2 maize population

Maize (Zea mays L.) breeders have used several genetic-statistical models to study the inheritance of quantitative traits. These models provide information on the importance of additive, dominance, and epistatic genetic variance for a quantitative trait. Estimates of genetic variances are useful in understanding heterosis and determining the response to selection. The objectives of this study were to estimate additive and dominance genetic variances and the average level of dominance for an F2 population derived from the B73 x Mo17 hybrid and use weighted least squares to determine the importance of digenic epistatic variances relative to additive and dominance variances. Genetic variances were estimated using Design III and weighted least squares analyses. Both analyses determined that dominance variance was more important than additive variance for grain yield. For other traits, additive genetic variance was more important than dominance variance. The average level of dominance suggests either overdominant gene effects were present for grain yield or pseudo-overdominance because of linkage disequilibrium in the F2 population. Epistatic variances generally were not significantly different from zero and therefore were relatively less important than additive and dominance variances. For several traits estimates of additive by additive epistatic variance decreased estimates of additive genetic variance, but generally the decrease in additive genetic variance was not significant.     

Effects of bottlenecks on quantitative genetic variation in the butterfly Bicyclus anynana

The effects of a single population bottleneck of differing severity on heritability and additive genetic variance was investigated experimentally using a butterfly. An outbred laboratory stock was used to found replicate lines with one pair, three pairs and 10 pairs of adults, as well as control lines with approximately 75 effective pairs. Heritability and additive genetic variance of eight wing pattern characters and wing size were estimated using parent-offspring covariances in the base population and in all daughter lines. Individual morphological characters and principal components of the nine characters showed a consistent pattern of treatment effects in which average heritability and additive genetic variance was lower in one pair and three pair lines than in 10 pair and control lines. Observed losses in heritability and additive genetic variance were significantly greater than predicted by the neutral additive model when calculated with coefficients of inbreeding estimated from demographic parameters alone. However, use of molecular markers revealed substantially more inbreeding, generated by increased variance in family size and background selection. Conservative interpretation of a statistical analysis incorporating this previously undetected inbreeding led to the conclusion that the response to inbreeding of the morphological traits studied showed no significant departure from the neutral additive model. This result is consistent with the evidence for minimal directional dominance for these traits. In contrast, egg hatching rate in the same experimental lines showed strong inbreeding depression, increased phenotypic variance and rapid response to selection, highly indicative of an increase in additive genetic variance due to dominance variance conversion.     

Contribution of genetic and environmental factors in the phenotypic variability of major indices of child development at different stages of postnatal ontogenesis

Main indices of physical development of monozygotic and dizygotic twins were investigated during 13 years period. Using the coefficients of the within-pair correlation of characters studied an attempt was made to estimate the correlative contribution of genetic and environmental determinants to formation of phenotypic variance of height, weight and chest circumference from birth up to 13 years old. The indices of composing components obtained suggest that underlying formation of phenotypic variance of each of the characters analysed are the mechanisms reflecting qualitative, quantitative and time peculiarities of functioning of polygenic systems involved in determination of characters studied and peculiarities of their interaction with environmental factors.     

Inheritance of finger pattern types in MZ and DZ twins

Digital patterns of a sample on twins were analyzed to estimate the resemblance between monozygotic (MZ) and dizygotic (DZ) twins and to evaluate the mode of inheritance by the use of maximum likelihood based variance decomposition analysis. MZ twin resemblance of finger pattern types appears to be more pronounced than in DZ twins, which suggests the presence of genetic factors in the forming of fingertip patterns. The most parsimonious model shows twin resemblance in count of all three basic finger patterns on 10 fingers. It has significant dominant genetic variance component across all fingers. In the general model, the dominant genetic variance component proportion is similar for all fingertips (about 60%) and the sibling environmental variance is significantly nonzero, but the proportion between additive and dominant variance components was different. Application of genetic model fitting technique of segregation analyses clearly shows mode of inheritance. A dominant genetic variance component or a specific genetic system modifies the phenotypic expression of the fingertip patterns. The present study provided evidence of strong genetic component in finger pattern types and seems more informative compared to the earlier traditional method of correlation analysis.     

Qualitative dermatoglyphic affinities between the migrant groups of fishermen of Puri Coast, India

Finger and palm prints of 677 subjects (395 males and 282 females) were analyzed for 11 qualitative dermatoglyphic variables to study the relationship between the three migrant groups of fishermen of Puri. Sanghvi's X2-distance gives configuration confirmatory to caste affiliations, quite clearly in males, but to a lesser degree in females. A comparison with distance configurations obtained for quantitative finger/palm variables and for anthropometric/genetic markers suggests that the qualitative dermatoglyphic traits stand out as useful markers in more convincingly portraying the affinities at the level of sub-castes.     

Comparing sensory experience in bitter taste perception of phenylthiocarbamide within and between human twins and singletons: intrapair differences in thresholds and genetic variance estimates

BACKGROUND: Quantitative genetic studies revealed that not all of the phenotypic variance in PTC taste perception is heritable. AIM: To study quantitative variations in PTC tasting ability in twins and to estimate heritability of PTC taste perception on the taste of twin data on males and females sexes separately. SUBJECTS AND METHODS: The data for PTC taste sensitivity following the classic method of Harris & Kalmus (1949) were collected on a sample of 141 twin pairs (66 MZ and 75 DZ) and 275 singletons (128 males and 147 females) from Chandigarh, India. Genetic analyses were performed following Christian (1979), Donner (1986) and Sham (1998). RESULTS: Frequency of non-tasters was similar in twins (33 %) and singletons (32 %), but significant sex differences were observed. No differences were found between zygosities for mean thresholds. Similarly, no evidence of variance heterogeneity and environmental covariance was seen between zygosities. Since no basic assumption of the twin method was found violated, within-pair estimates of genetic variance would be unbiased. These estimates were highly significant in both males and females. However, dominance and additive components of genetic variance were found to differ between sexes. CONCLUSION: PTC thresholds do not seem to be significantly affected by environmental factors as no variance inequality was observed between twin zygosities. Intensity of bitterness (scalar dimensions) of PTC is a separate trait having no commonality with the genetic basis of recognition threshold for PTC tasting ability. The receptors recognizing bitter taste are different from the receptors determining intensity of taste. The absolute difference between co-twins in PTC thresholds can be used as a simple tool in the twin zygosity diagnosis. The results show that none of the MZ co-twins had manifested difference of more than 3 in their PTC threshold.     

赫哲族掌指纹特征研究

本文对166名健康赫哲族人的掌指纹进行了研究,其中男性86名,女性80名。本文列出了58个赫哲族掌指纹参数,将其中52个掌指纹特征输入电子计算机,进行了相关及主成份分析。并且,将赫哲族的掌指纹特征与汉族的掌指纹特征进行了比较。 结果表明:赫哲族的掌指纹特征是与汉族相似的,并且有自己的特征;双手同名指的相关系数大于非同名指,单手相邻指的相关系数大于相隔指;在有关掌指纹特征的研究中,指纹的重要性大于掌纹。     

Dermatoglyphic changes during the population admixture between Kam and Han Chinese

Genetic studies and gene localization for human dermatoglyphs are currently ongoing. However, the inheritance modes of various genetic traits are not well understood because of the complexity of dermatoglyph genetics. The study of admixed populations can contribute to the understanding of population genetic traits of dermatoglyphs. Here, we present the dermatoglyphic characteristics of Kam and Liujia Han, and the admixed population consisting of these two parent populations.The characteristics of the admixed population do not always fall in the same ranges as the parent population characters but do seem to be biased to Kam or Liujia parent populations, depending on sex and ethnicity of parents. The total frequencies of different fingerprint types do not differ among these populations, but several of the quantitative traits and the palm true pattern frequencies do significantly differ between admixed and parent populations. The simple arch fingerprint frequency decreases significantly in the admixed population in comparison with parent populations while both simple whorl fingerprint frequency and finger ridge counts increase significantly. True pattern frequency of the span area of interdigital III and IV areas on right hands and the radial-loop frequency of the right index fingers in the admixed populations are consistent with their matrilineal population. These dermatoglyphic changes may result from increased heterozygosity in the admixed population. The genetic modes of these changes may be relatively simple and will be useful for future dermatoglyph genetic studies.      

Bias of heritability estimates from twin data in presence of errors of zygosity determination

Simple heritability estimators of continuous as well as discrete traits from twin data are known to overestimate the degree of genetic determination of the measured traits for several reasons. Errors of zygosity determination will, however, underestimate the true heritability. The bias due to wrong assignment of dizygous twin pairs into monozygous type is evaluated here, and the results indicate that this negative bias has a compensatory effect on the estimate of the degree of genetic determination when other factors of similarity between twin pairs are taken into account. It is shown that when an estimate of zygosity error is available, the bias due to this factor can be evaluated quantitatively, and hence the adjustment for zygosity error can be incorporated in the estimation of the degree of genetic determination of a trait. Although this theory is explicitly developed here for twin studies, the general principle also applies for other types of errors of determining the degree of biological relationships for estimation of heritability, in which case this type of error may be more important than the simple zygosity error.     

Joint-specific twin and familial aggregation of recalled physician diagnosed osteoarthritis.

In our three-stage questionnaire study we investigated patterns of twin and familial aggregation of osteoarthritis (OA) for commonly affected joints. The baseline questionnaire study of the Finnish Twin Cohort was performed in 1975. In 1990, 4095 twin pairs of the same gender born 1930-1957 responded to a questionnaire and reported whether they had OA diagnosed by a physician. In 1996 both twins of 266 pairs of which at least one had reported OA in 1990 responded to a detailed questionnaire on joint-specific OA, including family history of OA. In male pairs shared (non-genetic) familial effects accounted for 37% of the total variance in liability to OA and unshared environmental effects for 63%. In female pairs additive gene effects explained 44% of the variance in liability to OA, and unshared environmental effects for 36%. Familial aggregation of finger and knee OA was clearly higher than that of hip OA. Twin-pair discordance for OA was, to some extent, associated with body-mass index, occupational loading and trauma. Our results indicate that genetic effects may be modulated by sex or by environmental factors distributed differently between men and women. Based on our joint-specific data finger and knee joints are the most optimal targets for studies of genetic factors predisposing to the development of OA.     

Genome partitioning of genetic variation for height from 11,214 sibling pairs

Height has been used for more than a century as a model by which to understand quantitative genetic variation in humans. We report that the entire genome appears to contribute to its additive genetic variance. We used genotypes and phenotypes of 11,214 sibling pairs from three countries to partition additive genetic variance across the genome. Using genome scans to estimate the proportion of the genomes of each chromosome from siblings that were identical by descent, we estimated the heritability of height contributed by each of the 22 autosomes and the X chromosome. We show that additive genetic variance is spread across multiple chromosomes and that at least six chromosomes (i.e., 3, 4, 8, 15, 17, and 18) are responsible for the observed variation. Indeed, the data are not inconsistent with a uniform spread of trait loci throughout the genome. Our estimate of the variance explained by a chromosome is correlated with the number of times suggestive or significant linkage with height has been reported for that chromosome. Variance due to dominance was not significant but was difficult to assess because of the high sampling correlation between additive and dominance components. Results were consistent with the absence of any large between-chromosome epistatic effects. Notwithstanding the proposed architecture of complex traits that involves widespread gene-gene and gene-environment interactions, our results suggest that variation in height in humans can be explained by many loci distributed over all autosomes, with an additive mode of gene action.