Module 3 - Heredity and Prenatal Development

• Nature


  Heredity plays a crucial role in bringing about that feature
• Nurture


  Environment is most significant in shaping the way we are
• Almost all human features are polygenic (a result of many genes) and multifactorial (a result of many factors, both genetic and environmental)
• Genetic make-up


  Sets up a range of possibilities
• Genes may or may not be realized depending upon one's environmental experiences
• Bidirectional Interplay


  Environment affects the expression of genes just as genetic predispositions can impact a person's potentials
• Environmental circumstances can trigger symptoms of a genetic disorder (e.g. Diatheses-Stress Model or Psychological Disorders)
• Heritability


  A statistic that represents proportion of phenotypic variance that is due to genetic differences
• Intelligence is inherited, in a person's genetics
• Estimates of heritability of intelligence


  • 80% (Bouchard et al., 1990)
  • 50% (Plomin 1990, 1995)
• Environment


  Plays a significant role in a person's mental ability (e.g. education, SES, nutrition, parents' behavior, alcohol use, criminal behavior, emotional adaptation, amount of time spent reading or even watching television)
• Genes are segments of chromosomes that vary in length
• 46 strands of a chemical substance called DNA contained in the nucleus of each human cell
• Monozygotic (Identical Twins)


  Occur when a single zygote or fertilized egg split apart in the first two weeks of development
• Dizygotic (Fraternal Twins)


  Two eggs or ova are released and fertilized by two separate sperm
• Genotype


  The genetic complement, coded in DNA inherited from our parents
• No two people have identical genotypes except identical twins
• Phenotypes


  The expression of those genes in behavioral traits that we can measure
• Dominant genes


  Express themselves in the phenotype even when paired with a different version of the gene
• Recessive genes


  Express themselves only when paired with a similar version gene
• Incomplete dominance


  When a dominant gene does not entirely suppress the recessive gene
• Most characteristics are polygenic (not the result of a single gene, but of several genes)
• Chromosomal abnormality


  Occurs when a child inherits too many or too few chromosomes
• Down Syndrome (Trisomy 21)


  Occurs when the abnormal numbers occur on pair 21
• Sex-linked chromosomal disorders


  The disorder occurs on someone's pair #23 or the sex chromosomes
• Turner Syndrome


  Caused when all part of one of the X chromosomes is lost before or soon after conception due to a random event. The resulting zygote has an XO composition. Affects cognitive functioning and sexual maturation in girls. Infertility and short stature may be noted.
• Klinefelter Syndrome


  Caused when an extra X chromosome is present in the cells of a male due to a random event. The Y chromosome stimulates the growth of male genitals, but the extra X chromosomes inhabits this development. The male can have some breast development, infertility, and low levels of testosterone.
• Most of the known genetic disorders are dominant gene linked