AP PSYCHOLOGY: UNIT II Introductory Psychology: Biological Bases of Behavior “We share half of our genes with a banana…” – Robert May Topic: Behavior Genetics

What is Behavior Genetics? Behavior Genetics  The study of the relative power & limits of genetics and environmental influences on behavior  Nature v. nurture

PART ONE The Biological Bases: Basic Genetic Principles

Basics: Genes – Our Code for Life Chromosomes Strands of DNA (deoxyribonucleic acid) that carry genetic information; located in the nucleus of every human cell  Humans: 46 chromosomes (23/23) Genes  DNA segments; key functional units in hereditary transmission  Can be active (expressed) or inactive Autosomes Sex Chromosomes

Basics: Genes – Our Code for Life Like chromosomes, genes operate in pairs, with one gene in each pair coming from each parent  Homozygous Condition  Paired genes are the same  Heterozygous Condition  Paired genes are different  In this case, one gene in the pair masks the other

Basics: Genes – Our Code for Life Genotype  A person’s genetic makeup; determined at conception and fixed forever Phenotype  The ways in which a person’s genotype is manifested in observable characteristics; may change over time  **Different genotypes can yield the same phenotype  **Genes are pliable Polygenic Inheritance  Characteristics that are influenced by more than one pair of genes

Basics: Genes – Our Code for Life Genetic & Chromosomal Problems  Cystic Fibrosis  Two recessive genes; respiratory & digestive tract  Sickle Cell Anemia  Two recessive genes; blood disorder  Tay-Sachs Disorder  Two recessive genes; fatal neurological disorder  Phenylketonuria  Two recessive genes; difficulty digesting a certain amino acid – phenylalanine

Basics: Genes – Our Code for Life Genetic & Chromosomal Problems  Down Syndrome  Extra chromosome (21 st pair)  Klinefelter’s Syndrome  Extra X chromosome; reduced masculine characteristics (e.g. enlarged breasts, obesity, etc.)  Turner’s Syndrome  Missing X chromosome (e.g. infertility, sexually underdeveloped, etc.)

PART TWO The Biological Bases: Heritability The ultimate nature- versus-nurture laboratory

What is Heritability? The extent to which the differences among people are attributable to their differing genes  What percentage of the difference among height can be attributed to genes?  90%  Individual differences v. group differences?  Nature v. Nurture?

Heritability: Twin Studies Monozygotic Dizygotic

Heritability: Twin Studies Used to determine the heritability of a trait

Heritability: Jim Lewis Middle class Wife: Betty Son: James Alan Dog: Toy Hobby: Woodworking Bad Habits: Chain smoker, fingernail biter… Other: Drove a Chevy, watched stock-car racing & drank Miller… Conditions: High blood pressure & migraines…

Heritability: Jim Springer In 1980, Jim Springer called Jim Lewis (37 year separation)  Everything down to their dog’s name was the same (except sons James Allan & James Alan) When listening to each other's voices, they would mistake themselves for the other First in Thomas Bouchard’s “Minnesota Twin Study”

Heritability: Adoption Studies Compare children's’ traits with those of their biological and adopted parents  Studies suggest that adoptees tend to be more similar to their biological parents  Two adopted children in the same household bear no more resemblance to each other than two biological siblings (in terms of personality)

Heritability: Adoption Studies S0 does parenting even have an effect?  YES!  It has an effect on biologically related and unrelated children alike  Effects attitudes, values, manners, beliefs, faith, etc.  Different from personality…  “Heredity deals the cards, environment plays the hand…”

PART THREE The Biological Bases: Molecular Genetics DEFINITION: A branch extension of behavior genetics that asks the question, “Do specific genes influence behavior?” GOAL: To find some of the many genes that influence normal human traits (e.g. body weight, sexual orientation, extraversion)