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R Plomin

Publications and source records attributed to R Plomin.

At least 19 recordsLinked to original sources
PubMed2014

Genetics and intelligence differences: five special findings.

Intelligence is a core construct in differential psychology and behavioural genetics, and should be so in cognitive neuroscience. It is one of the best predictors of important life outcomes such as education, occupation, mental and physical health and illness, and mortality. Intelligence is one of the most heritable behavioural traits. Here, we highlight five genetic findings that are special to intelligence differences and that have important implications for its genetic architecture and for gene-hunting expeditions. (i) The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood. (ii) Intelligence captures genetic effects on diverse cognitive and learning abilities, which correlate phenotypically about 0.30 on average but correlate genetically about 0.60 or higher. (iii) Assortative mating is greater for intelligence (spouse correlations ~0.40) than for other behavioural traits such as personality and psychopathology (~0.10) or physical traits such as height and weight (~0.20). Assortative mating pumps additive genetic variance into the population every generation, contributing to the high narrow heritability (additive genetic variance) of intelligence. (iv) Unlike psychiatric disorders, intelligence is normally distributed with a positive end of exceptional performance that is a model for 'positive genetics'. (v) Intelligence is associated with education and social class and broadens the causal perspectives on how these three inter-correlated variables contribute to social mobility, and health, illness and mortality differences. These five findings arose primarily from twin studies. They are being confirmed by the first new quantitative genetic technique in a century-Genome-wide Complex Trait Analysis (GCTA)-which estimates genetic influence using genome-wide genotypes in large samples of unrelated individuals. Comparing GCTA results to the results of twin studies reveals important insights into the genetic architecture of intelligence that are relevant to attempts to narrow the 'missing heritability' gap.

Genetic Predisposition to Disease↗
PubMed1992

Single-locus control of saccharin intake in BXD/Ty recombinant inbred (RI) mice: some methodological implications for RI strain analysis.

The sac locus, with a major effect on saccharin preference, was discovered by Fuller (1974) in C57BL/6J (B6), DBA/2J (D2), and derived crosses, and is now supported in the BXD/Ty recombinant inbred (RI) series by a marked bimodal distribution in saccharin preference among 20 strains. The B6 allele led to increased saccharin preference compared to the D2 allele. Since the search for bimodal distributions reflecting major gene loci is an essential part of RI strain analysis, a new statistical method is proposed to test for bimodality, and comparisons are made to previously proposed methods. Another new RI method, quantitative trait loci (QTL) analysis, allows provisional detection and mapping of minor as well as major gene loci. Using this method as a screen, significant associations with saccharin preference were suggested with marker loci on portions of six chromosomes. One of these, the D12nyu1 locus on chromosome 12, was independently supported in a panel of standard (non-RI) inbred strains also tested for saccharin preference. It is unclear whether this reflects the sac locus.

Animals↗
PubMed1992

The use of CXB recombinant inbred mice to detect quantitative trait loci in behavior.

Although recombinant inbred (RI) series of mice have been developed to identify and map single-gene characteristics, they can also be used to identify quantitative trait loci (QTL) that account for small amounts of variance in quantitative traits such as behavior. We applied an RI QTL approach to the analysis of published behavioral data from seven studies that used the CXB RI series of mice. Nearly all of the behaviors showed strain distribution patterns indicative of multiple-gene rather than single-gene influence. Although the CXB series is limited to seven RI strains, RI QTL association analysis suggests QTL candidate markers for several behaviors, including avoidance and exploration.

Animals↗
PubMed1992

Importance of shared genes and shared environments for symptoms of depression in older adults.

The Center for Epidemiologic Studies-Depression scale was administered to 68 identical and 161 fraternal twin pairs reared apart and 114 identical and 138 fraternal pairs reared together to ascertain relative genetic and environmental contributions to individual differences in self-reported depressive symptoms. Intraclass correlations and model fitting indicated that genetic influences explained 16% of the variance in total depression scores and 19% for the Psychomotor Retardation and Somatic Complaints subscale, but heritability was minimal for the Depressed Mood and Well-Being subscales. Influence of family rearing context played a substantial role in explaining twin similarity, whereas unique life experiences accounted for the greatest proportion of variance. Significant age group differences were observed, with heritability greater in twins of 60 years of age or older than in twins under 60, especially for Psychomotor Retardation.

Adoption↗
PubMed1992

Age differences in genetic and environmental influences for health from the Swedish Adoption/Twin Study of Aging.

This cross-sectional study explored the etiology of variability in self-reported health. The sample comprises adult twins participating in the Swedish Adoption/Twin Study of Aging and includes identical (MZ) and fraternal (DZ) twin pairs who have been reared together or reared apart. Two different components of overall health status are analyzed: an index of chronic health problems and self-rated health. Height and weight were included to assess the representativeness of the twin data. Individual differences increased across age for both measures of health, and there were significant age differences in the genetic and environmental etiologies of this variation. Genetic variance showed a twofold increase for chronic illness up until age 70. Environmental influences during adulthood appear important later in life. For self-rated health, genetic effects were important in the older age groups; however, the increase in total variation is predominantly due to unique environmental influences.

Adoption↗
PubMed1992

Temperament, emotion, and cognition at fourteen months: the MacArthur Longitudinal Twin Study.

200 pairs of twins were assessed at 14 months of age in the laboratory and home. Measures were obtained of temperament, emotion, and cognition/language. Comparisons between identical and fraternal twin correlations suggest that individual differences are due in part to heritable influences. For temperament, genetic influence was significant for behavioral observations of inhibition to the unfamiliar, tester ratings of activity, and parental ratings of temperament. For emotion, significant genetic influence was found for empathy and parental ratings of negative emotion. The estimate of heritability for parental report of expression of negative emotions was relatively high, whereas that for expression of positive emotions was low, a finding consistent with previous research. For cognition and language, genetic influence was significant for behavioral indices of spatial memory, categorization, and word comprehension. Shared rearing environment appears influential for parental reports of language and for positive emotions, but not for other measures of emotion or for temperament.

Cognition↗
PubMed1979

Multivariate behavioral genetic analysis of twin data on scholastic abilities.

Multivariate behavioral genetic analyses may employ either genetic and environmental correlations or phenotypically standardized covariances to assess the structure of genetic and environmental influences. Correlations and phenotypically standardized covariances answer different questions--correlations are appropriate for understanding the nature of genetic and environmental influences, whereas covariances are appropriate for determining the etiology of phenotypic correlations. The ratio of the genetic and environmental covariances to the phenotypic correlation yields estimates of bivariate heritability and environmentality, measures of the extent to which observed phenotypic covariance is due to genetic and environmental influences. Multivariate analyses of genetic and environmental correlations and covariances are illustrated with twin data on scholastic abilities. Factor analyses of correlations suggest that the same set of genes affects the major areas of academic achievement and that the environmental influences are similarly structured. Analyses of phenotypically standardized covariances indicate that the structures of genetic and environmental influences as they contribute to phenotypic resemblance among scholastic abilities are both similar and simple: there are one general genetic factor and one general environmental factor. Bivariate heritabilities and environmentalities are similar in magnitude, indicating that the strong phenotypic relationship among scholastic abilities is due roughly equally o genetic and environmental influences.

Analysis of Variance↗
PubMed1979

A multivariate twin analysis of within-family environmental influences in infants' social responsiveness.

Observational measures of social responsiveness were obtained for twin infants. The structure of within-family environmental influences was assessed by correlating identical twin pair differences for 13 behaviors in seven social settings. Factor analysis of the difference score matrix yielded one interpretable factor. This factor indicated that within-family environmental influences were not completely random but may exert a systematic effect on social behavior in several situations.

Child, Preschool↗
PubMed1977

Assortative mating by unwed biological parents of adopted children.

Analyses of data obtained from 662 unwed couples whose children were relinquished for adoption reveal that biological parents of adopted children mate assortatively. For physical characters, assortative mating of unwed parents was similar to that of wed parents; for behavior characters, however, there was less assortative mating by the unwed parents. Because assortative mating inflates estimates of genetic parameters in adoption studies, future studies should collect information on both biological parents.

Adoption↗
PubMed1977

A twin study of temperament in young children.

Temperament was assessed in 182 young children (91 pairs of twins, average age of 3.6 years) with use of the Colorado Childhood Temperament Inventory (CCTI). The CCTI represents a merger of dimensions suggested by two approaches to the study of the development of temperament: the New York Longitudinal Study and Buss and Plomin's temperament theory. Of the six traits measured by the CCTI, genetic factors were implicated in the etiology of five (sociability, emotionality, activity, attention span-persistence, and soothability). One trait, reaction to food, showed no genetic influence and indicated strong between-family environmental effects. A negative correlation between emotionality and soothability may also have a genetic basis. These results suggest that the development of certain personality traits--those that we include as temperament--are substantially influenced by heredity.

Attention↗
PubMed1977

Temperament in early childhood.

The structure of temperament proposed by the New York Longitudinal Study (NYLS) of Thomas and collaborators (1963, 1968) was compared to Buss and Plomin's (1975) EASI temperament theory. An objective inventory was developed for the NYLS temperaments. Mothers rated 182 children on both NYLS and EASI temperaments. Only two of the nine NYLS dimensions, attention span-persistence and distractibility, were supported by factor analysis. The four EASI dimensions (emotionality, activity, sociability, and impulsivity) were replicated. A similar sociability factor emerged from both the NYLS and EASI systems, but other temperaments were unique. The NYLS and EASI systems were merged to form the Colorado Childhood Temperament Inventory, a parental rating instrument for children 1-6 years of age.

Attention↗
PubMed1976

Heritability of personality traits in adult male twins.

Personality test data from the California Psychological Inventory were collected on 99 pairs of identical and 99 pairs of fraternal adult male twins. Heritabilities were comuted for all 18 scales and compared to the heritabilities for "pure" scales with overlapping items omitted. Two of the pure scales, Responsibility and Femininity, had zero heritabilities, whereas all of the full scales had moderate to high heritabilities. It was concluded that item overlap has contributed significantly to previous failures to find evidence for the differential heritability of personality traits as measured by the CPI. CPI items were classified into genetic or environmental categories and separate factor analyses of items in these categories revealed more differences than similarities in factor structure. The genetic personality factors included Conversational Poise, Compulsiveness, and Social Ease. Environmental factors included Confidence in Leadership, Impulse Control, Philosophical Attitudes, Intellectual Interest, and Exhibitionism. Compared to the genetic factors, each of the environmental factors accounted for only a very small percentage of the variance.

Adult↗
PubMed1976

Resemblance in appearance and the equal environments assumption in twin studies of personality traits.

The equal environments hypothesis of twin methodology was examined for the variable of similarity of appearance as it affects the personality ratings of young twins. There were two separate samples, the first with 95 pairs of same-sex twins and the second with 111 pairs. The average age of the twins in both samples was 3-1/2 years. Mothers rated their twins on four personality traits and on confusability of appearance. Not surprisingly, identical twins were markedly more similar in appearance than fraternal twins. The effect of this inequality on the personality ratings of the two types of twins was examined by correlating ratings of similarity of appearance with the absolute difference on the four personality traits for each pair of twins. None of the correlations was significant for the identical twins, suggesting that greater resemblance in appearance in identical twins does not make them more similar in personality. Indeed, the data suggested a contrast effect in which identical twins who were easily mistaken in appearance tended to be rated as less similar in personality. Thus, although similarity of appearance may create unequal environments for the two types of twins, it does not appear to bias twin studies in the direction of inflated heritabilities, at least for rating studies of the personality of young twins.

Child, Preschool↗