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Thread: Behavior Genetics

  1. #11
    Senior Member cosmocreator's Avatar
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    Post Intelligence

    Intelligence


    The results of over 50 years of research on the similarity in intelligence between relatives (as estimated by intelligence, or IQ, scores) indicate that identical twins reared apart are remarkably similar relative to adopted individuals reared in the same home (see illus. ). Identical twins reared together are much more similar than fraternal twins reared together, and dramatically more similar than unrelated individuals reared together. This general evidence clearly suggests that heredity is an important determinant of population variation in intelligence. It has been determined that approximately40-70% of the variation in intelligence can be explained by hereditary factors. See also: Intelligence

  2. #12
    Senior Member cosmocreator's Avatar
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    Post Special mental abilities

    Special mental abilities


    Intelligence (IQ) tests, while controversial, are felt by many to be a measure of general intelligence. Other special mental abilities exist, such as spatial orientation (the ability to rotate three-dimensional figures mentally) and perceptual speed and accuracy (the ability to detect errors in text quickly). It is possible to ask if profiles of abilities (patterns of strengths and weaknesses) are influenced by heredity.

    Scores on the various subtests of the Wechsler intelligence scales can be thought of as reflecting measures of some of these special mental abilities. Two studies examined the correlations of the patterns of subtest scores in young twins. The first used the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) to measure 70 pairs of identical and 46 pairs of fraternal 6-year-old twins. The correlations are 0.43 and 0.27, respectively. The second study measured 69 identical and 35 fraternal pairs, with a mean age of 8 years, on the Wechsler Intelligence Scale for Children (WISC-R) and obtained correlations of 0.45 and 0.24, respectively. Data from the Minnesota Study of Twins Reared Apart, using the Wechsler Adult Intelligence Scale (WAIS) score from 32 pairs of identical twins reared apart and 13 pairs of fraternal twins reared apart, provide correlations of 0.52 and 0.12. The finding that the fraternal twins are approximately half as similar as the identical twins, and the similarity of results across age groups, despite the use of different instruments, strongly support the conclusion of a significant genetic influence on the patterning of mental abilities.

  3. #13
    Senior Member cosmocreator's Avatar
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    Post Developmental genetics and behavior

    Developmental genetics and behavior


    The Louisville Twin Study followed nearly 500 pairs of twins since infancy as part of a longitudinal study of mental development. The results showed that developmental profilesthe spurts and lags in mental development over time, as measured by several age-appropriate testsare more similar in identical twins than in fraternal twins. This evidence suggests that genes turn on and off during the course of mental development and influence behavior much the same way as they influence physical development (for example, children also show spurts and lags in growth). The Louisville data also show that the degree of similarity between identical twins, and between parents and offspring, increases over time; the degree of similarity between fraternal twins, while high very early in life, decreases. The correlations between both types of twins at age 15 are very close to those expected under a simple polygenic model.

    These synchronous patterns of change show that mental development is under the control of genetic processes that unfold throughout childhood and adolescence. While the environment provided by parents is important in allowing children to maximize their developmental potential, the pattern of growth and the ultimate degree of similarity between relatives strongly reflect the effects of their shared genes. Identical twins reared in different families from a very young age are almost as similar on some traits as identical twins reared together.

  4. #14
    Senior Member cosmocreator's Avatar
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    Post Personality

    Personality


    Personality inventories measure such characteristics as introversion and extroversion, well-being, aggression, risk-taking and traditionalism. Many psychologists, while accepting the possibility of genetic influences on intelligence and mental abilities, believe that common family environmental factors are the principal determinants of personality traits. The evidence is, however, quite to the contrary. A number of adoption studies have demonstrated only modest degrees of similarity between genetically unrelated individuals who are reared together. A study comparing reared-apart and reared-together identical twins on a number of personality, psychological interest, and social attitude scales found that the correlations on each measure were very similar for both groups of twins (see table ). These findings suggest that genetic differences account for about half the group variability for these characteristics and that common family environment did not make the reared-together twins any more similar than the reared-apart twins. The remainder of the variability (and the reason the identical twins do not have a correlation of 1.0) must be due largely to the unique or unshared environments experienced by each twin. See also: Personality theory

  5. #15
    Senior Member cosmocreator's Avatar
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    Post Psychopathology

    Psychopathology


    While twin, family, and adoption studies support the role of the genes in the development of schizophrenia and the affective disorders (depression and manic-depression), the environment plays an important role: among identical twin pairs in which one twin is affected, the cotwin is often unaffected. However, if the offspring of members of such discordant twin pairs are examined, the risk of being affected is the same in the offspring of the unaffected twin as in those of the affected twin, demonstrating that the unaffected twin did indeed carry the disease alleles. Early excitement generated by reports of mapping schizophrenia to chromosome 5 and manic-depressive illness (or bipolar disorder) to chromosomes 11 and X has been curbed by failure to replicate findings in other affected families or even in the same families at a later time. While reports of linkage of manic-depressive illness to the X chromosome have seemed more robust than linkage of the disorder to chromosome 11, a reanalysis of several large families finds weakened support for a gene on the X chromosome in two of the three families. Reasons for the revised findings in these studies of psychopathologies include the possibility of incorrect diagnoses in previous studies; individuals becoming affected who were not previously, since many behavioral disorders often do not show up until adulthood; and the use of DNA markers for the later analyses (earlier ones were often based on phenotypic markers). Availability of informative DNA markers for all regions of all the chromosomes will eventually be realized, in large part through the Human Genome Initiative. Researchers will continue to look for genes that contribute to these disorders. See also: Affective disorders; Schizophrenia

  6. #16
    Senior Member cosmocreator's Avatar
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    Post Alcoholism

    Alcoholism


    As in the psychopathologies, data accumulated over many years from twin, family, and adoption studies point to genetic influences on alcoholism. This view is also supported by the ability to breed selectively for sensitivity to ethanol and for ethanol-related behaviors in animals such as rats and mice. In humans, certain alleles of genes that code for the alcohol-metabolizing enzymes, alcohol dehydrogenase and aldehyde dehydrogenase, are found in different frequencies in alcoholic and nonalcoholic Chinese men. In spite of these findings, there has been little evidence for linkage of alcoholism to a particular gene or genes. Alcoholism is a very complex disorder, and it is expected that many genes, some conferring primary risks and others that interact with them, as well as numerous environmental variables and gene-environment interactions, are contributory. See also: Alcoholism; Psychology

  7. #17
    Senior Member cosmocreator's Avatar
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    Post Source:

    Kimerly J. Wilcox

    Thomas J. Bouchard, Jr.

    BIBLIOGRAPHY E. L. Gershon and R. O. Reider, Major disorders of mind and brain, Sci. Amer., 267(3):126-133, 1992
    R. Plomin, J. Owen, and P. McGuffin, The genetic basis of complex human behavior, Science, 264:1733-1739, June 1994
    S. Scarr, Developmental theories for the 1990s: Development and individual differences, Child Dev., 63:1-19, 1992
    R. S. Wilson, The Louisville twin study: Developmental synchronies in behavior, Child Dev., 54(2):298-316, 1983

  8. #18
    Member sThygesen's Avatar
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    my family

    on the dane side we all have anger issues and anyone who starts drinking is an alcoholic lol i know for sure it runs in the family...

  9. #19
    Senior Member Kriemhild's Avatar
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    Good article. I think that genetics certainly play some sort of role in predetermining an individual's behavioral traits. For instance, depression and bipolar disorder seem to almost "run" in my paternal grandfather's side.

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