Genetics and Behavior

  1. Instinct or innate behavior is the inherent inclination of a living organism towards a particular complex behavior.
  2. A learned behavior is a change in the range of organism's actions or mannerisms as a result of experience.
  3. The adaptive value represents the combined influence of all characters which affect the fitness of an individual or population.
  4. An adaptation is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection.
  5. Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.
  6. The phrase nature vs. nurture relates to the relative importance of an individual's innate qualities as compared to an individual's personal experiences in causing individual differences, especially in behavioral traits.
  7. Concordance is the probability that a pair of individuals will both have a certain characteristic, given that one of the pair has the characteristic.
  8. Considered a key tool in behavioral genetics and in content fields, from biology to psychology, twin studies reveal the absolute and relative importance of environmental and genetic influences on individuals in a sample.
    9. This chart illustrates three patterns one might see when studying the influence of genes and environment on traits in individuals. Trait A shows a high sibling correlation, but little heritability (i.e. high shared environmental variance c2; low heritability h2). Trait B shows a high heritability since correlation of trait rises sharply with degree of genetic similarity. Trait C shows low heritability, but also low correlations generally; this means Trait C has a high nonshared environmental variance e2. In other words, the degree to which individuals display Trait C has little to do with either genes or broadly predictable environmental factors. The outcome approaches random for an individual. Notice also that even identical twins raised in a common family rarely show 100% trait correlation.

    This chart illustrates three patterns one might see when studying the influence of genes and environment on traits in individuals. Trait A shows a high sibling correlation, but little heritability (i.e. high shared environmental variance c2; low heritability h2). Trait B shows a high heritability since correlation of trait rises sharply with degree of genetic similarity. Trait C shows low heritability, but also low correlations generally; this means Trait C has a high nonshared environmental variance e2. In other words, the degree to which individuals display Trait C has little to do with either genes or broadly predictable environmental factors—roughly, the outcome approaches random for an individual. Notice also that even identical twins raised in a common family rarely show 100% trait correlation.

  9. Monozygotic twins (identical twins) occur when a single egg is fertilized to form one zygote which then divides into two separate embryos.
  10. Dizygotic twins (fraternal twins) usually occur when two fertilized eggs are implanted in the uterus wall at the same time.
  11. The adoption study is a classic tool of behavioral genetics. The adoptees method investigates similarities between the adoptees and their biological and adoptive parents. The familial method compares non-biological siblings who are reared in the same household.