Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: Behavior Genetics

  1. #1
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Behavior Genetics

    http://www.accessscience.com/

    The hereditary factors of behavior may be studied in animals and humans. Charles Darwin, who originated the theory that natural selection is the basis of biological evolution, was persuaded by Francis Galton that the principles of natural selection applied to behavior as well as physical characteristics. Members of a species vary in the expression of certain behaviors because of variations in their genes, and these behaviors have survival value in some environments. One example of such a behavior is curiositysome organisms are more curious than others, and in some settings curiosity is advantageous for survival. Therefore, in those environments more of the organisms that express curiosity survive to reproduce than do those that lack this trait.

    The science of behavior genetics is an extension of these ideas and seeks (1) to determine to what extent the variation of a trait in a population (the extent of individual differences) is due to genetic processes, to what extent it is due to environmental variation, and to what extent it is due to joint functions of these factors (heredity-environment interactions and correlations); and (2) to identify the genetic architecture (genotypes) that underlies behavior.

    Traditionally, some of the clearest and most indisputable evidence for a hereditary influence on behavior comes from selective-breeding experiments with animals. Behavior genetic research has utilized bacteria, paramecia, nematodes, fruit flies, moths, houseflies, mosquitoes, wasps, bees, crickets, fishes, geese, cows, dogs, and numerous other organisms. Breeding of these organisms allows genetically useful types of relationships, such as half-sibs, to be produced easily. Although not all of this work involves breeding experiments, enough of it does to demonstrate conclusively the importance of genetic processes on behavior in every species examined. Artificial selection (selective breeding) can be used to obtain a population that scores high or low on specific traits. Inbred strains of many animals (populations that are made up of individuals which are nearly identical genetically as a result of inbreeding), particularly rodents, are readily available, and the study of various types of crosses among them can provide a wealth of information. An experimental design using the recombinant inbred-strain method shows great promise for isolating single-gene effects. This procedure derives several inbred strains from the F2 generation (grandchildren) produced by a cross between two initial inbred strains. Since it is possible to exert a great deal of control over the rearing environments, the experimenter can manipulate both heredity and environment, a feat virtually impossible in human studies but required for precise answers to behavior genetic questions.

    Other work has focused on the effects of the environment and genotype-environment interactions. For example, experiments with mice have shown that, with respect to several learning tasks, early environmental-enrichment effects and maternal effects were quite small, relative to the amount of normal genetic variation found in the strains of mice tested. Only a few genotype-environment interactions were found. Still other work has shown that early experiences affect later behavior patterns for some strains but not others (a genotype-environment interaction).

    An increasing role for animals in genetic research is to provide models of human genetic diseases, many of which have behavioral features. Such animal models may occur naturally or may be engineered in the laboratory. For example, a mouse model was produced which is deficient in the enzyme HPRT. Deficiency of this enzyme in humans is due to a recessive X-linked gene and leads to a disorder known as Lesch-Nyhan syndrome, which is characterized by self-injurious behavior and mental retardation. Animal models are available for many other neurobehavioral disorders, including narcolepsy, various epilepsies, and alcoholism. The availability of animal models allows researchers to obtain information about the development of genetic disorders and the effects of different environments on this development, as well as to explore treatment options. While it is not always prudent or desirable to generalize from animal results to humans, it is assumed that basic genetic systems work in similar ways across organisms, and it is likely that these types of animal studies will play a key role in elucidating the ways in which environment influences phenotypic variation. With advances in genetic technology, it is possible to observe genetic variation more directly by locating, identifying, and characterizing genes themselves.
    Last edited by cosmocreator; Friday, October 31st, 2003 at 04:17 AM.

  2. #2
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Chromosomes and Genes

    Chromosomes and Genes


    In most organisms, chromosomes are linear structures comprising strands of deoxyribonucleic acid (DNA) and accompanying proteins. A gene is a specific segment of DNA representing the genetic information for making a needed protein or for regulating other genes. Each gene may come in several variations, called alleles, that may produce somewhat different phenotypic outcomes. An organism's phenotype, or complement of observable properties, is due to the combined effects of its genetic information and the environmental conditions it experiences. See also: Chromosome; Gene

    Each human inherits 23 paternal chromosomes and 23 maternal chromosomes at fertilization. Genes occupy (fairly) specific positions on these chromosomes. Located in the nucleus of each cell, the 46 chromosomes can be thought of as comprising 23 pairs, with one member of each pair coming from each parent; for example, the maternal chromosome 1 pairs with the paternal chromosome 1, the maternal chromosome 15 pairs with the paternal chromosome 15, and so on. These are called homologous pairs. Thus, at the same location on each member of the pair, there is a gene for a particular kind of genetic information, or two genes of that kind per individual. Since each chromosome in the pair comes from one parent, each gene in the pair comes from one parent. This is true for the first 22 pairs of chromosomes, called the autosomes. The twenty-third pair is the sex chromosomes, and they may or may not be the same. A female has two X chromosomes (designated 46, XX), but a male has one X chromosome and one Y chromosome (46, XY). The Y chromosome contains crucial genetic information that causes an embryo to develop as a male. Thus, a mother can contribute only an X chromosome to her offspring, but a father can contribute either an X or a Y chromosome. It is, therefore, the father who determines the sex of the offspring. See also: Human genetics; Sex determination

    The Y chromosome is smaller than the X chromosome and contains less genetic material. Consequently, few genes that reside on the X and Y chromosomes are paired. Traits influenced by genes carried only on the X chromosome are called X-linked, while genes carried only on the Y chromosome are called holandric genes. Red-green color blindness is under the control of a recessive variant (allele) of a gene on the X chromosome. This allele is called recessive, and the gene for normal color vision is called dominant because, in females, the gene for red-green color blindness must be present on both X chromosomes in order for the female to be red-green color-blind. One dominant normal color vision gene can override one defective gene. In the male, however, the situation is different, because this X-chromosome gene does not have a matching gene on the Y chromosome. If the X chromosome carries the defective version of the gene and is matched with a Y chromosome, that individual is red-green color-blind. Females can only be red-green color-blind if both genes at that location are recessive, so this behavioral trait is more frequent among males than females. See also: Dominance; Sex-linked inheritance

  3. #3
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Chromosome abnormalities

    Chromosome abnormalities


    There are a number of abnormalities involving entire chromosomes or pieces of chromosomes, rather than isolated genes, that influence behavior, and many important ones involve the sex chromosomes. The reason is that most abnormalities of the autosomes are lethal during fetal development. It is estimated that as many as 50% of all conceptuses have gross chromosomal abnormalities, while these defects are found in only 0.5% of newborns. It seems that an excess of chromosomal material is better tolerated than a deficit; even so, when a newborn is found to have an extra autosome, it is usually one of the smaller chromosomes, such as 13, 18, or 21. See also: Chromosome aberration; Congenital anomalies

  4. #4
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Autosomal chromosome anomalies

    Autosomal chromosome anomalies

    The abnormal presence or absence of autosomes is usually lethal in the early stages of fetal development. There are, however, several exceptions. The best known is Down syndrome, or trisomy 21, in which there is an extra twenty-first chromosome (47, +21), occurring in about 1 in 700 live births. The physical features of these individuals are striking: round face with broad head, small medial epicanthal fold, flattened bridge of the nose, small ears and nose, and protruding tongue. Skeletal and congenital heart defects are common, as is increased susceptibility to respiratory infections. Down children have a reduced life expectancy, although modern antibiotics and heart surgery have improved this somewhat. Although the IQ of these individuals ranges from less than 25 to about 75, with a mean of 40-50, many can be taught to read and write and to care for themselves.

    Other kinds of chromosomal abnormalities exist, including duplications, rearrangements, and deletions of various amounts of chromosomal material. In most cases, the more chromosomal material involved, the more deleterious the outcome. However, it is becoming apparent that even very small deletions and duplications can lead to serious disorders, although these usually are considered single gene disorders rather than chromosomal abnormalities. For example, the abnormal repetition of three of the units (base pairs) that make up the gene's DNA has been implicated in, among others, Fragile X, Huntington's disease, a progressive neurological disorder, and myotonic dystrophy, characterized by muscle spasms and muscle wasting, cataract, and other features.

  5. #5
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Sex chromosome anomalies

    Sex chromosome anomalies

    Most sex chromosome anomalies involve the presence of one or more extra X or Y chromosomes, such as XXX, XXY, XXXX, or XYY. An exception is Turner syndrome, in which only one complete X chromosome is present (45, X). [In some cases, part of a second X may be present. In a few individuals, some cells have two X chromosomes while others have only one; these individuals are referred to as mosaics.] Each type of sex chromosome anomaly has specific features or abnormalities associated with it. For example, most individuals with Turner syndrome have only one sex chromosome, an X, but are phenotypically female. Physical features commonly found in these individuals include webbed neck, short stature (usually less than 5 ft or 150 cm), streak gonads, infantile genitalia, shield chest, and widely spaced nipples. Pubic and underarm hair may or may not be present. Since the ovaries do not develop, the women do not menstruate and are sterile. However, not all of these features are present in all individuals with Turner syndrome. There are certain behavioral characteristics that have been associated with women having Turner syndrome, such as a lack of aggressive tendencies, reduced libido, and strong inhibitions; today, however, there is some question about whether these characteristics are due in part to the way these short, immature-looking women are treated by others. Sex hormone therapy can help to increase height somewhat and to induce physical maturation; such changes may have psychological benefits as well. Intelligence is usually in the normal range in Turner syndrome, although the individuals may have deficits in space-form recognition and directional sense. See also: Down syndrome

    Another type of sex chromosome abnormality leads to the Fragile X syndrome. The name derives from a fragile site on the long arm of the X chromosome which can be seen when cells are grown under special conditions. Affected males usually have some characteristic facial features, enlarged testes, and mental retardation. The Fragile X syndrome is the most frequent known cause of mental retardation in males. Females with one Fragile X chromosome and one normal X chromosome may have a lesser degree of mental retardation.

  6. #6
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Variations in genes

    Variations in genes


    Far more common than chromosome abnormalities are variations in the genes themselves. Most of these variations lead to differences among individuals which are considered normal, for example, variations in eye color. Some gene variations, however, lead to differences which are not considered normal, such as Huntington's disease, albinism (lack of pigment in hair, skin, and eyes), or hemophilia (lack of blood clotting factors). It is now known that some differences among individuals are due to variations in single genes, while others are due to the combined effects of two or more genes (polygenic or continuous characters). It must also be remembered that the environment is always involved in the expression of a trait.

    Single-gene effects

    The effects of a single gene on behavior have been most extensively studied in the domain of mental retardation. Research has shown that there are a large number of metabolic pathways (series of chemical reactions used by cells to make or break down molecules) which have defects due to a single gene. Over 100 of these defects influence mental ability. See also: Mental retardation

    One such single-gene defect is classic phenylketonuria (PKU), an autosomal recessive disorder, which also illustrates the role that environment can play in the expression of a trait. Individuals who are homozygous (having two copies of the PKU allele) are unable to make the enzyme phenylalanine hydroxylase, which converts the essential amino acid phenylalanine to tyrosine, a nonessential amino acid. Instead, the excess phenylalanine builds up in the blood and is converted into phenylpyruvic acid, which is toxic to the developing nervous system in large amounts. The main effect of untreated PKU is severe mental retardation, along with a distinctive odor, light pigmentation, unusual gait and posture, and seizures. Many untreated individuals with PKU show fearfulness, irritability, and violent outbursts of temper. The treatment for PKU consists of a diet that severely restricts phenylalanine intake. If the diet is carefully maintained from the first few weeks of life through about 8-10 years of age, PKU individuals have a good chance of developing normal or near-normal intelligence. Most states in the United States now require that newborns be tested for PKU before leaving the hospital. See also: Phenylketonuria

    Polygenic effects

    Most of the traits of interest to behavioral scientists are continuous (ranging from low to high, such as intelligence) rather than discontinuous (for example, affected or unaffected with PKU). They are continuous because they are under the control of many genes, each having a small effect (polygenic). Thus, a trait governed by a single gene usually shows two or three discrete phenotypic categories. A polygenic trait shows a distribution of phenotypes that approximates a normal curve. For some types of behavior, the question of whether it is caused by a single gene or whether it is a polygenic trait has not been settled, and the role played by the environment is at issue.

  7. #7
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Nature or Nurture Question

    Nature or Nurture Question


    Every organism develops in a particular environment, and both genes and environment control development. It is, therefore, not possible to state that a particular behavioral trait is either genetic or environmental in origin. It is possible, however, to investigate the relative contributions of heredity and environment to the variation among individuals in a population. With humans, it is possible to obtain approximate results by measuring the similarity among relatives on the trait of interest.

    The most widely used measure of similarity is the correlation coefficient. This measure varies from -1 to +1. If a large number of pairs of people were selected at random from a population and then compared, each pair's scores on some measure (for example, a physical variable such as height, or a psychological variable, such as extroversion), the degree of similarity among them, as measured by a correlation coefficient, would be zero. The reason is that, on the average, they would be genetically unrelated and would have been reared in different environments, and therefore would be unlikely to be similar on that measure, regardless of the influence of heredity or environment. In order to obtain information about these influences, scientists compare individuals who are related or who have shared environments. Because related individuals usually share some environments as well as genes, it is useful, but not absolutely necessary, to compare the results with those from the relatives that have been reared apart.

  8. #8
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Twin and adoption studies

    Twin and adoption studies


    Twins are often used in behavior genetic studies. One method compares the similarity within pairs of both identical (monozygotic or one-egg) twins and fraternal (dizygotic or two-egg) twins reared together. Identical twins have all their genes in common by descent, since they arise from a single fertilized egg. Fraternal twins arise from two fertilized eggs and so, like any pair of nontwin siblings, share on average one-half of their genes. (Parents and offspring share exactly half of their genes, as described earlier.) If it is assumed that the effects of the shared environments of the two types of twins are equal (a testable assumption), greater resemblance between identical twins than fraternal twins should reflect the proportion of genes they share, and the difference between the correlations of the two twin types should represent about one-half the genetic effect.

    A second type of twin study compares not only twins reared together but twins who have been reared apart. The degree of similarity between identical twins reared in the same home would reflect the fact that all their genes are identical and that they share a common family environment. On the other hand, if identical twins can be located who had been adopted by different families chosen at random (an unlikely event, since adopted children tend to be selectively placed), a measure of their degree of similarity would reflect only the effect of their common genes. If it were true that an individual's level on a measure (for example, height or extroversion score) is determined in large part by the characteristics of his or her family and the opportunities that the family makes available to him or her, reared-apart identical twins should be no more alike than pairs of individuals chosen at random. If they do exhibit some degree of similarity, it would reflect genetic effects alone. The existence of even very large genetic effects, however, would in no way imply that the environment was unimportant in the development of the trait; it would simply imply that environment was less important than genes in determining the variation among individuals on the trait in question at the time of measurement. That is, the individuals would differ more because of the genes they carry than because of the particular environments to which they were exposed. In another range of environments, the results might be different.

    Another method of determining the relative importance of genes and environment is to compare the degree of similarity of unrelated individuals raised in the same family: adopted children and their adoptive parents and siblings. Any similarity between these individuals would be due entirely to common family environment and not to genes (barring placement in similar families). Family, twin, and adoption studies have their respective advantages and limitations; when results from different kinds of studies are similar regarding a particular trait, they can be viewed with increased confidence.

    In addition, biometric and other quantitative methods allow information from many types of family relationships to be processed simultaneously. These approaches estimate the different genetic and environmental components of variance for a trait. They do this by estimating the phenotypic variances and covariances of measurements from different types of biological and adoptive relationships, for example, biological parent-offspring, adoptive parent-offspring, biological sib-sib, identical twins, fraternal twins, and so on. These estimates then allow the fitting or testing of models which predict certain amounts of genetic and environmental variance. Finding the best-fitting model leads to a better understanding of the underlying genetic (and environmental) architecture of a trait. Finally, modern genetic technology is being applied to single-gene conditions with behavioral components. One approach analyzes DNA from populations of affected and unaffected individuals to determine if a known, or candidate, gene (chosen because its function conceivably could contribute to the observed phenotype) could be the gene in question. Abnormal alleles of genes affecting neurons in the brain, such as those coding for neurotransmitters and their receptors and for ion channels, among others, are being explored as candidate genes for certain behavioral disorders. Several candidate genes for schizophrenia have been ruled out. See also: Biometrics; Twins (human)

  9. #9
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Gene mapping

    Gene mapping


    Gene mapping or linkage analysis is a technology in which a gene is localized to a specific position on a chromosome. The DNA from affected and unaffected members of families is analyzed to find an association between the disease state and the presence of a gene or a piece of DNA whose position is known, called a marker. The assumption is that if the association is very high it is due to the fact that the gene involved in the trait under investigation and the marker DNA are physically close (linked) on the chromosome. Various techniques can then be used to identify the DNA that makes up the gene itself. One of the very first genes to be localized to a particular chromosome by this method was that for the progressive neurological disorder Huntington's disease (located on chromosome 4). Once a gene has been identified, its function can be determined and studied and treatment options considered. Linkage analysis is applied most often to the study of genetic disorders, also can be used to learn more about genes contributing to normal variation.

    Gene mapping is a powerful tool that is widely applied. However, it cannot always provide answers to genetic questions. Its success depends upon several factors, including understanding of the mode of transmission of the gene (for example, whether the allele of interest is dominant or recessive, on an autosome or the X chromosome), having the correct diagnosis, and assuming that the trait in question is due to the same genes in all the individuals who have the trait (genetic homogeneity). Alzheimer's disease provides an illustration of genetic heterogeneity, being found in familial and nonfamilial as well as early- and late-onset forms. Three chromosomal locations have been identified among groups of families with inherited Alzheimer's diseasechromosome 19 for late-onset, and 14 and 21 for early-onset types. In addition, gene mapping requires that markers for the appropriate chromosomal locations are available and that the families being studied show some variation in allelic forms of these markers. See also: Alzheimer's disease

    Behavioral traits often present special challenges for this type of analysis. The mode of inheritance is often not known with confidence. It is widely believed that many, if not most, behavioral traits are polygenic in nature. If each gene involved has only a small effect, it will be difficult to identify the genes by mapping alone. However, biometric techniques developed for analysis of polygenic traits in plants (quantitative trait loci, or QTL, methods) can be used in animals, sometimes in conjunction with recombinant inbred strains. Another potential difficulty with behavioral traits is making an accurate, or at least consistent, diagnosis. Inclusion of too many or too few characteristics in a diagnosis will lead to incorrect categorization of some individuals in each family studied and will produce spurious results. Finally, it is thought that genetic heterogeneity may be common in behavioral traits; if it is not identified, results of linkage analyses may be inconclusive.

  10. #10
    Senior Member
    cosmocreator's Avatar
    Join Date
    Dec 2002
    Last Online
    Thursday, January 18th, 2007 @ 06:36 PM
    Subrace
    Other
    Gender
    Age
    55
    Politics
    Living in the real world
    Posts
    3,850
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    8
    Thanked in
    8 Posts

    Post Environmental variables

    Environmental variables


    Developmental psychologists are finding that differences in children's behavioral phenotypes are due more to their different genotypes than to their different rearing environments, as long as those environments are within a normal range of experiences. Identifying environmental variables from this normal range that have an important effect on the behavioral phenotype may be even more difficult than identifying contributing genes. Advances in theory and new technologies, combined with information from more traditional methodologies, will continue to provide insight into the contributions of genes and environment to behavior.

Page 1 of 2 12 LastLast

Similar Threads

  1. Warfare and Human Behavior
    By SwordOfTheVistula in forum Psychology, Behavior, & Neuroscience
    Replies: 0
    Last Post: Thursday, November 13th, 2008, 06:59 AM
  2. Explosive Behavior
    By Dagna in forum Psychology, Behavior, & Neuroscience
    Replies: 1
    Last Post: Sunday, May 11th, 2008, 09:28 PM
  3. Does Behavior Indicates Sub-Race?
    By Aspire in forum Physical Anthropology
    Replies: 8
    Last Post: Sunday, September 3rd, 2006, 02:39 AM
  4. Can the Weather Affect Behavior?
    By Bridie in forum Psychology, Behavior, & Neuroscience
    Replies: 6
    Last Post: Sunday, April 2nd, 2006, 12:40 PM
  5. Sociobiology: Explaining Human Behavior
    By Agrippa in forum Psychology, Behavior, & Neuroscience
    Replies: 0
    Last Post: Tuesday, December 13th, 2005, 08:15 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •