Chapter 3 Biology and Behavior

Each of us is a product of our genetics and the environment Historical views of how characteristics are transmitted  Galton (1869)  Mendel  Watson and Crick (1953)  Currently scientists are attempting to figure out the function of the roughtly 30,000 to 60,000 genes that make up the human genome Nature and Nurture

Divisions of the Cell

Mitosis refers to a process by which 2 identical cells are produced Meiosis refers to a process in 4 cells are produced, with each containing only 23 chromosomes (Figure adapted with permission from Biology: Exploring Life, by G.D. Brum and L.K. McKane, 1989, New York: John Wiley and Sons)

Cross-Over During Meiosis During meiosis, the x-shaped chromosomes line up and intermix, yielding a novel genetic product (Figure adapted with permission from Biology: Exploring Life, by G.D. Brum and L.K. McKane, 1989, New York: John Wiley and Sons)

DNA DNA is the basic genetic material, formed from pairs of base nucleotides –The bases form pairs such as adenosine-thymine or guanine-cytosine –The DNA strand is in the form of a double helix made up of series of base pairs

Principles of Heredity Mendel argued that certain traits are transmitted from parents to child –Each trait is governed by two elements with one from each parent –Phenotype –Genotype –Principle of dominance

Mendelian Inheritance

© 1999 John Wiley and Sons, Inc. Genetic Disorders Dominant disorders: –Huntington’s chorea Recessive disorders: –Phenylketonuria (PKU)

Genetic and Environmental Forces Model Components:  Genotype  Phenotype  Environment 4 relations fundamental to a child’s development  Parents’ genotype Child’s genotype  Child’s genotype Child’s phenotype  Child’s environment Child’s phenotype  Child’s phenotype Child’s environment

Parents’ GenotypeChild’s Genotype Terms:  Chromosomes  DNA  Genes  Proteins Chromosomes  Sex Determination by Sex Chromosomes  Females XX  Males XY—presence of the Y chromosome determines male sex Diversity Mutations— Crossing over

Child’s Genotype Child’s Phenotype Gene Expression  Regulator genes control other genes (puberty, graying hair) Dominance Patterns  Inheritance patterns are complicated with few following Mendel’s simple pattern  Alleles  Dominance/Recessive genes  Homozygous/Heterozygous

Mendelian inheritance patterns Above are the Mendelian inheritance patterns for two brown-haired parents who are both heterozygous for hair color. The allele for brown hair (B) is dominant, and that for blond hair (b) is recessive. Note that these parents have three chances out of four of producing children with brown hair. They have two chances in four of producing brown-haired children who carry the gene for blond hair.

© 1999 John Wiley and Sons, Inc. Common Genetic Traits Brown eyesBlue, gray, or green eyes Normal hairBaldness (in men) Dark hairBlond hair Color visionColor Blindness FrecklesNo freckles DimplesNo dimples DOMINANT RECESSIVE

Genetic Transmission of Diseases and Disorders  Dominant–Recessive Pattern—  2 recessive alleles (PKU, sickle-cell anemia, Tay-Sachs)  Dominant gene (Huntington’s disease)  Polygenic Inheritance—combination of multiple genes and environment (ADHD, some cancers, schizophrenia)  Sex-Linked Inheritance  X-linked Disorders are more prevalent in men (hemophilia, color-blindness, male-pattern baldness)  Chromosomal Anomalies—more or less than the normal complement of chromosomes (Down syndrome, Kleinfelter syndrome, Turner syndrome)  Regulator Gene Defects—which initiate the development of genitalia

Child’s EnvironmentChild’s Phenotype Depending on the environment–genotype relationship numerous phenotypes may result  PKU—special diet  Parents’ role—highly literate parents may have more books in the home, exposing children to more literature Child’s PhenotypeChild’s Environment For example, the activity level of a child gets differing responses from adults Children create environments of interest, talents, and personality

Behavioral Genetics The study of how variation results from environmental factors and genetic  Research Designs  Family studies  Twin studies  Adoption studies

Age-Related Changes in Concordance for MZ and DZ Twins (Figure adapted by permission from “The Louisville Twin Study: Developmental Synchronies in Behavior” by R.S. Wilson, 1983, Child Development, 34, p Copyright © 1983 by the Society for Research in Child Development).

Heritability  A statistical estimate of the proportion of the measured variance on a given trait among individuals in a given population that is attributable to genetic differences among the individuals  For example IQ, temperament, and divorce  Important restrictions:  Heritability applies only to populations, not to individuals  Heritability estimates apply only to a particular group living in a particular environment at a particular time  High heritability does not imply immutability  Heritability estimates tell us nothing about difference between groups

Experience and the Brain Plasticity  Experience-expectant plasticity  Sensitive periods  Experience-dependent plasticity Plasticity, Brain Damage, and Recovery  Recovery depends on  Extent of the damage  Aspect of the brain developing at time of damage  Damage may not be immediate  “Worst time” is during prenatal development  “Best time” is childhood during synapse generation and pruning

Body Growth and Development Depends on nature and nurture, genetics, and the environment Nutritional Behavior  Breast feeding  Food preference  Eating disorders  Obesity  Bulimia  Anorexia Nervosa  Undernutrition  Marasmus (low calories)  Kwashiorkor (low protein) Research has shown links between cognitive development/performance and nutrition

Malnutrition and cognitive development Malnutrition, combined with poverty, affects many aspects of development and can lead to impaired cognitive abilities. (From Brown & Pollitt, 1996.)