Lesson 2: Genetics And Environmental Of Behavior

• Chromosomes


  Structures in the nucleus of a cell containing DNA coiled around histone proteins
• Human beings have 46 chromosomes (23 pairs)
• Two types of chromosomes

  • Autosomes
  • Sex chromosomes
• Autosomes


  Contain the remainder of a person's genetic information (22 pairs)
• Sex chromosomes


  Some genetic traits are linked to a person's sex and therefore passed on by the sex chromosomes (remaining pair, either XX female or XY male)
• Chromosomal abnormalities


  • Can occur during fetal development if something goes wrong during replication of the cells
  • Examples: Down Syndrome, Klinefelter Syndrome, Turner Syndrome
• Sex-linked genes


  Genes that are carried by either sex chromosome
• Men have X and Y sex chromosomes, women have XX sex chromosomes
• Only men inherit Y-linked traits, both men and women can inherit X-linked traits
• 1. linked recessive traits are primarily expressed in the observable characteristics of men
• Women are frequently carriers of X-linked traits but more rarely have them expressed in their own phenotypes
• Examples of X-linked genetic conditions

  • Hemophilia
  • Duchenne muscular dystrophy
  • Fragile-X syndrome
  • Some high blood pressure
  • Congenital night blindness
  • G6PD (glucose-6-phosphate dehydrogenase) deficiency
  • Red-green color blindness
  • Male pattern baldness
• Sex-limited genes


  When the characters are physically expressed in one sex only, but the gene is present in both sexes
• In the presence of hormones, sex-limited genes are activated
• Sex-limited traits


  • Beard controlling gene
  • Milk secretion gene
  • Egg-laying
• Genotype-environment correlations (GEC)


  Refer to genetic differences in exposure to particular events
• Three types of genotype-environment correlations

  • Passive GEC
  • Evocative (reactive) GEC
  • Active (selective) GEC
• Passive GEC


  Association between the genotype of a child from his/her parents and the environment in which the child is raised
• Passive GEC


  • Parents with histories of antisocial behavior (heritable) are at increased risk of abusing their children
• Evocative (reactive) GEC


  Association between an individual's genetically influenced behavior and others' reactions to that behavior
• Evocative (reactive) GEC


  • A shy child (partly genetically influenced) may be less fun to other children, making other children less likely to want to spend with him/her
• Active (selective) GEC


  Association between an individual's genetic propensities and the environmental niches that individual selects
• Active (selective) GEC


  • A shy person is likely to choose quiet activities and less boisterous environments
  • Children who are musically inclined seek out music instruction and opportunities that facilitate their natural musical ability
• Behavior genetics


  Studies heritability of behavioral traits and overlaps with genetics, psychology, and ethology
• Genetics plays a large role in when and how learning, growing, and development occurs