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

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

The Biological Bases: Basic Genetic Principles Part one

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 Segments of DNA molecules Contain code for production of proteins Key functional units in hereditary transmission (biological development) Sex Chromosomes Autosomes

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 Person’s actual physical characteristics Height, eye color, disease history, general disposition Different genotypes can yield the same phenotype May change over time

Basics: Genes – Our Code for Life Genetic & Chromosomal Problems Cystic Fibrosis Two recessive genes; Disorder that affects respiratory & digestive tract Sickle Cell Anemia Two recessive genes; blood disorder Abnormality in shape of red blood cells Tay-Sachs Disorder Two recessive genes; fatal neurological disorder Destroys nerve cells in the brain and spinal cord

Basics: Genes – Our Code for Life Genetic & Chromosomal Problems Down Syndrome Extra chromosome (21st pair) Causes lifelong intellectual disability, developmental delays, and health problems Turner Syndrome Missing X chromosome (e.g. infertility, sexually underdeveloped, etc.)

The Biological Bases: Heritability Part two Twin studies: The ultimate nature-versus-nurture laboratory

What is Heritability? The extent to which the differences among people are attributable to their genes Studies focus on: Individual differences v. Group differences? Obesity: (2010) Americans – 28% Japanese – 3% Nature v. Nurture? We all have the capacity to learn language, but we do not all speak the exact same

Heritability: Twin Studies Monozygotic Dizygotic

Heritability: Jim Lewis & Jim Springer Middle class Wife: Betty Son: James Alan (Allan) Dog: Toy Hobby: Woodworking Bad Habits: Chain smoker, fingernail biting Other: Drove a Chevy, watched stock-car racing Health conditions: High blood pressure & occasional migraines Identical twins Gerald Levey and Mark Newman

Idealized View of an Adoption Study Parent-offspring resemblance can arise for both genetic and environmental reasons Genetic and environmental contributions to parent-offspring; Resemblance are in principle separate Bio and Rearing Parent Birth Parent Adoptive Parent Genetic Environmental Genetic Environmental Offspring Offspring

Heritability: Twin Studies Used to determine the heritability of a trait https://www.youtube.com/watch?v=IyT2AlzzzQs

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? It has an effect on biologically related and unrelated children alike Early stimulation is key to proper development Effects attitudes, values, manners, beliefs, faith, etc. Different from temperament and personality… “Heredity deals the cards, environment plays the hand…”

“Mutation and natural selection are the engines of evolution” Genetic mutations What causes a genetic mutation? How often do mutations occur? How have mutations been of benefit to the human population? https://www.youtube.com/watch?v=qVmusHZtQms

Nature vs. Nurture and Gender

Sexual Birth Defects Ambiguous genitalia Androgen insensitivity syndrome (AIS) Fetal tissue insensitivity to male hormones Affects genital development Congenital adrenal hyperplasia (CAH) Inherited condition – affects hormone production Excessive manufacture of male hormones Sex chromosome disorders Baby has mixture of XX and XY sex chromosomes Y chromosome may be inactive; one of X chromosomes may have a tine Y segment attached Maternal factors Other factors during pregnancy that impact hormone production

Understanding Gender Gender roles Social learning theory Our expectations about the way men and women behave Influenced by culture Gender identity Sense of being male or female Gender-typing Exhibiting traditional gender traits and interests Transgender Persons whose gender identity, gender expression or behavior does not conform to sex assigned at birth Social learning theory Children learn gender-linked behavior by observing and imitating and being rewarded or punished Gender schema theory Concept of what it means to be male or female Gender becomes lens through which we view our experiences Based on social learning theory How have gender roles changed over time? Why? Identify traditional gender roles Should transgender students be allowed to use restrooms of sex with which they identify? In what ways are gender-linked behavior attributed to the social learning theory?