Evidence for directional non-additivity in the genetics of finger ridge counts

Three Patterns of Inheritance of Quantitative Dermatoglyphic Traits: Kosovo Albanian Twin Study

Dermatoglyphs are epidermal ridge configurations on the fingers, palms and soles that are formed during fetal development, and therefore only the intrauterine environment can have any influence on their formation. This study aims at investigating the genetic and environmental contribution in determining quantitative dermatoglyphic traits in 32 monozygotic (MZ) and 35 dizygotic (DZ) same-sex twins from the Albanian population of Kosovo. All genetic analyses were run in the statistical program Mx. After assumptions testing, based on the pattern of MZ-DZ correlations, univariate models were fitted to the data in order to estimate additive genetic (A), common (C) and individual (E) environmental influences for all variables. The exception was the atd-angle for which a model with nonadditive genetic (D) influences was tested, since DZ correlations were less than half of MZ correlations. Goodness of fit of the full ACE or ADE model was compared to the saturated model. The fit of nested models (AE, CE, DE or E) was compared to the full models (ACE or ADE). Our results indicate that additive genetic component strongly contributes to individual differences in finger ridge counts (49-81%), and weakly (0-50%) on the formation of the palmar ridge counts between the palmar triradii a, b, c, and d. The specific pattern found for the atd-angle implies the impact of a nonadditive genetic component, possibly the effect of a major gene. Further, more powered studies are needed to confirm this pattern, especially for resolving the issue of the huge difference in MZ and DZ twin similarity for the atd-angle palmar trait.

Digital Dermatoglyphic Heritability Differences as Evidenced by a Female Twin Study

The genetic and environmental contributions to determine digital dermatoglyphic traits were investigated by using female dizygotic and monozygotic twin pairs to estimate heritability indexes (h2). The evaluated sample was composed by 20 monozygotic twin pairs and 13 dizygotic twin pairs. A significant heritability (h2 = 0.65 to 0.96) was observed for 12 dermatoglyphic characteristics (delta indexes and ridge counts for right hand, left hand and both hands, and ridge counts for most individual fingers). A negative correlation between the ridge counts and heritability indexes from individual fingers was found for the left hand, which appears to be associated to a higher arch pattern frequency in most left-hand fingers, since this frequency was negatively correlated with ridge counts and positively correlated with heritability indexes. Heritability indexes of right-hand fingers were positively correlated with loop pattern frequency and negatively correlated with whorl pattern frequency. The low heritability of ridge counts from left thumb, ring and little fingers (h2 = 0.11 to 0.32) indicates a higher chance that the chorion type had an influence in the intra-pair variance of monozygotic twins. Results confirmed the predominant genetic influence on the total ridge count. The heritability indexes varied in up to 8 times between different fingers and its association to ridge counts and pattern frequency was very variable between hands, evidencing that the use of dermatoglyphic traits from individual fingers as indicators of genetic influences to other human traits should consider this variability.

Genetic modeling of primary tooth emergence: a study of Australian twins

The aim of this study was to quantify contributions of genetic and environmental factors to variation in timing of emergence of the primary teeth in a sample of monozygotic and dizygotic twins, using univariate model-fitting approaches. The sample comprised 94 pairs of monozygotic twins and 125 pairs of dizygous twins, all of European ancestry, aged from 2-6 years. Tooth emergence timing was based on parental report, with a subset of data validated by clinical assessment. Heritability estimates for tooth emergence timing were generally high, around 90%, however estimates for the lower right lateral incisor and the lower canines were around 50%. These findings confirm a strong genetic influence on observed variation in the timing of emergence of the human primary teeth.

Effects of genetic and environmental factors on the a-b, b-c and c-d interdigital ridge counts

A study of 100 MZ (55 female and 45 male) and 97 DZ (50 male and 47 female) same-sexed twin pairs was carried out to analyse the genetic component of the variance of the a-b, b-c and c-d interdigital ridge counts by means of the Christian method. Especially for the a-b interdigital ridge count, we found it important to analyse both sexes separately. Our results suggest that the a-b count in males seems to be more influenced by environmental factors than the other counts. For females, the three interdigital counts seem to have a strong genetic component influencing their phenotypic expression. Factor analysis with VARIMAX rotation showed each interdigital ridge count to be genetically independent.

Complex segregation analysis of quantitative dermatoglyphic traits in five Indian populations

OBJECTIVE

Dermatoglyphics is widely used as a genetically determined trait in anthropogenetics although the genetic nature of its inheritance is still inconclusive, due to the lack of any established genetic model to resolve the existing inconsistencies in the literature. However, advanced statistical packages for complex segregation analyses are available and the aim of the present study is to determine the mode of dermatoglyphic trait inheritance in five different ethnic populations.

METHODS

Five hundred families (2435 individuals) of two generations were used for principal component analysis, familial correlation and segregation analysis (package MAN-5).

RESULTS

The similarity of three factors suggests a common internal structure. Significant familial correlation (except spouse) indicates the involvement of a familial component in the variation of dermatoglyphic traits. Segregation analyses suggest the transmission of a genetic effect in the families which follows the Mendelian model and confirms a major gene effect on factor 1 and factor 2 with two co-dominant alleles. There is no evidence of a major gene effect or environmental effect on factor 3 (a-b ridge counts). The nature of transmission and trait variance (H2) strongly supports the existence of a common nature of dermatoglyphic trait inheritance in populations, irrespective of ethnic and geographic area.

CONCLUSION

Major gene involvement in finger dermatoglyphics according to Mendelian models is confirmed.

Genetic analysis of deciduous tooth size in Australian twins

Investigations of permanent dental crown size in twins and family groups indicate a high degree of transmissible control, but little is known about the relative contributions of genetic and environmental factors to variation in size of the deciduous (primary) teeth. Here, maximum mesiodistal and buccolingual crown dimensions of maxillary and mandibular primary teeth were measured from dental models of 602 individuals, including 99 monozygous (MZ) twin pairs, 81 dizygous (DZ) same-sex pairs, 41 DZ opposite-sex pairs, and 160 singletons. Data were subjected to univariate genetic analysis with the structural-equation-modelling package, Mx using the normal assumptions of the twin model. A model incorporating additive genetic (A) and unique environmental (E) variation was found to be the most parsimonious for all tooth-size variables. Estimates of heritability for deciduous crown size ranged from 0.62 to 0.91. This study shows that variation in deciduous crown size has a strong genetic component, similar to that observed in the permanent dentition. Further studies are required to determine whether the underlying genetic mechanisms are the same for both deciduous and permanent teeth.

Variation among European populations in summary finger ridge-count variables

The magnitude of ridge-count variation and its spatial and linguistic patterning was examined using 82 male and 75 female samples from Europe. Variables were summary measures: sum of radial counts (radial) sum of ulnar counts (ulnar) and sum of larger counts (total ridge-count or TRC). Dermatoglyphic parameters were compared with those derived from classic nuclear gene markers. Fst values computed from ridge-counts range between 0.016 and 0.025, relatively high when compared to classical genetic polymorphism. Ridge-count distances show significant correlation with geographic distances but not with linguistic distances. Ridge-count distances show even higher correlation with blood marker distances, suggesting that, like blood polymorphisms, ridge-counts were strongly influenced by demic expansion of Neolithic farmers. The most differentiated populations in Europe are those of the North Atlantic and North Sea region, especially the Orcadians and Faroe Islanders. Certain Finnic speakers such as Lapps and Udmurts are also strongly differentiated. These same populations are frequent outliers in genetic analyses.

Genetic covariance structure of incisor crown size in twins

Previous studies of tooth size in twins and their families have suggested a high degree of genetic control, although there have been difficulties separating the various genetic and environmental effects. A genetic analysis of variation in crown size of the permanent incisors of South Australian twins was carried out, with structural equation modeling used to determine the relative contributions of genetic and environmental factors. Maximum mesiodistal crown dimensions of maxillary and mandibular permanent incisors were recorded from dental models of 298 pairs of twins, including 149 monozygous (MZ) and 149 dizygous (DZ) pairs. The analysis revealed that: (i) an adequate fit required additive genetic and unique environmental components; (ii) augmenting the model with non-additive genetic variation did not lead to a significant improvement in fit; (iii) there was evidence of shared environmental influences in the upper central incisors of males; (iv) the additive genetic component constituted a general factor loading on all eight teeth, with group factors loading on antimeric pairs of teeth; (v) unique environmental effects were mostly variable-specific; (vi) most factor loadings on antimeric tooth pairs could be constrained to be equal, indicating a symmetry of genetic and environmental influences between left and right sides; and (vii) estimated heritability of the incisor mesiodistal dimensions varied from 0.81 to 0.91.

Cechy dermatoglificzne człowieka. Przegląd koncepcji i metod badań

The review was made from the point of view of genetic transmission, source of variability, morphogenesis and functional significance of these traits in men. While pointing the reasons of hitherto failures in solving the primary problems, the difficulties in defining the traits were stressed. The critical review on some dermatoglyphic opinions and new trends of researches in Poland and in the world were presented.

Cechy dermatoglificzne człowieka. Przegląd koncepcji i metod badań

The review was made from the point of view of genetic transmission, source of variability, morphogenesis and functional significance of these traits in men. While pointing the reasons of hitherto failures in solving the primary problems, the difficulties in defining the traits were stressed. The critical review on some dermatoglyphic opinions and new trends of researches in Poland and in the world were presented.

Relationships of epidermal ridge patterns with body measurements and their possible evolutionary significance

It is commonly believed that in humans epidermal ridge patterns are in regression relative to nonhuman primates, and they play no role in adaptive processes. In contrast with this we have found relationships between anthropometric and dermatoglyphic measurements in a sample of 61 normal males. Anthropometric variables included limb, trunk, head, and face measures. Dermatoglyphic variables included finger ridge counts and pattern intensities and ridge breadth in the palmar interdigital area II. The strongest relationship is between the type and size of pattern on the thumb and the breadth of ridges, and wrist width, which accounts for nearly 30% of the total variance in these traits. These findings identify previously unknown sources of variation in dermatoglyphic patterns and indicate that the dermatoglyphic-anthropometric relationships might have resulted from selection pressures in evolution of modern man.

Dermal ridge patterns and fertility in a Polish rural sample

The relationship between ridge counts and pattern intensities on fingers, palms and soles, and number of pregnancies, number of surviving children, maternal age at birth of first child, and miscarriages was investigated in a rural Polish sample of 273 females. All subjects had completed their reproduction by the time of investigation and the use of contraceptives was negligible. Results show that females with a history of miscarriage have lower mean ridge counts on all fingers and lower pattern intensity on all fingers except V, with statistically significant differences for fingers III and IV. The results also suggest a relationship between the intensity of patterns on fingers II and V and in thenar areas, with the number of pregnancies and/or surviving offspring. The limitations of the present data and a need for more specific investigations are discussed.

Causes of variation in drinking habits in a large twin sample

A genetic analysis of alcohol consumption in 3810 pairs of adult twins is reported. When no correction was made for age, individual environmental variance, including non-repeatable errors of reporting, accounted for approximately 44% of variation in both sexes. In females, there was no evidence of shared environmental effects and 56% of the variance was genetic in origin. In males, only 36% of the variance was genetic and common environmental effects accounted for the remaining 20% of individual differences. For females, the results for younger (30 years and under) and older (over 30) twins were similar. For males, however, the effect of age was striking. In younger male twins over 60% of the variance was genetic in origin, with the remaining variance due to environmental influences unique to the individual. In older twins genetic differences do not appear to be important, with approximately 50% of the total variance due to individual environmental differences and the remaining 50% due to the effect of the common family environment. Our results suggest that both age and sex need to be considered when analysing the causes of variation in alcohol consumption.

Finger ridge patterns and tactile sensitivity

Tactile sensitivity has been measured in 101 normal individuals (38 females and 63 males) of European origin, and compared with ridge pattern characteristics of the fourth fingertip of the right hand. There is a relationship of tactile sensitivity performance with the type of pattern, particularly in females, and also with the number of junctions within the pattern, particularly in males. The possible origin of sex differences in tactile sensitivity and in its relationships with dermatoglyphic variables is discussed. In spite of sex differences, optimal tactile sensitivity performance seems to be associated with medium-sized loop patterns which have a greater number of junctions than ends and also have grooves wider than ridges. The possible evolutionary significance of these associations is discussed in relation to evidence for epistatic genetic variation for pattern intensity.

Evidence for a major gene effect in the distributions of digital ridge counts

Previous attempts to isolate major gene effects in digital dermatoglyphics have been approached from two main directions. One has been concerned with analysing the components of total ridge count (TRC) distributions and examining various parameters of these distributions. The other has concentrated on the inheritance of various combinations of digital patterns. This study is primarily concerned with the shape of TRC and digital ridge count distributions. It suggests that a major gene effect may be as conspicuous in the distributions of digital counts as it is in TRC if these are viewed from the standpoint of global variation. The relationship between mean TRC, the standard deviation of TRC, skewness and kurtosis is examined and the results are compared with those obtained from a simple major locus model in which the overall distribution of TRC is composed of three overlapping normal distributions. As predicted by the model there is a negative correlation between mean TRC and its standard deviation, also a positive correlation with kurtosis. The expected relationship between mean TRC and skewness is non-linear, taking the form of an asymmetric U-shaped curve. There is evidence that the relationship between mean TRC and g1 in population samples covering a wide range of mean total ridge count follows this trend. The concordance between the predicted relationships and the observed frequency distributions is taken as evidence in favour of a single major locus hypothesis.

A genetical analysis of covariation between finger ridge counts

1. The genetical and environmental structure of covariation between finger ridge counts in twin and sibling data has been analysed using the method of Martin and Eaves (1977) adapted from Jöreskog. 2. The model for environmental covariance contains a single factor loading on all ten digits but most environmental variance is specific to each finger. 3. For additive genetic variance there is one common factor loading on all digits. There are also five other independent factors, one for each digit. The thumb factor loads only on the two thumbs but the four fingers load on the finger in question and on the adjacent fingers. 4. A single common factor for non-additive genetic variance produces a considerable improvement in the model. 5. The pattern of genetic effects differs between left and right hands. 6. Although the same model is appropriate for males and females, different parameters estimates are required. 7. The fit of models is sensitive to the scale of measurement.

A genetical analysis of diversity and asymmetry in finger ridge counts

The genetics of asymmetry and diversity of finger ridge counts in man has been examined by jointly regressing the individual counts of each hand on to the mean values summed over left and right hands in a sample of twins. The resulting asymmetry terms are largely under environmental control but with a small significant genetic component. The diversity items show a larger degree of genetic control with a suggestion of dominance or additive X additive epistasis.