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AP Psychology 2.2 Behavioral Genetics Genetics Besides the functioning of the endocrine and nervous system, genetics is another biological factor that affects human behavior and thought • Behavioral Genetics – Genetic and environmental contributions to personality and behavior • Human traits are usually caused by genes acting together (not usually one gene) Nature vs. Nurture • Influence on behavior (ex…body shape, introversion, temper) • Gene-Environment Interaction (sometimes hard to determine because genes cause someone to chooser their enviroment) – Nature – heredity (genes determine) – Nurture – environment or life history (begins in prenatal period) Evolutionary Psychologists • Study how natural selection favored behaviors that contributed to survival and spread of our ancestors genes • Look at universal behaviors shared by all people Behavioral Geneticists • Study the role played by our genes and our environment in personality characteristics and behavior (mental ability, emotional stability, temperament, personality, interests, etc.) • Look at the cause of our individual differences • Gene-environment Interaction – choose environ because of genes Twin Studies • Help separate the contributions of heredity and environment • Zygote – fertilized egg • Identical (monozygotic) twins – Two individuals who share all of the same genes/heredity because they develop from the same zygote • Fraternal (dizygotic) twins – Siblings that share about half of the same genes because they develop from two different zygotes Twin Studies • Heritability – variation among individuals that is due to genetic causes (genes) • When twins grow up in the same environment, the extent to which identical twins are behaviorally more similar than fraternal twins reveal the contribution of heredity • If fraternal twins are separated at birth and raised in different environments (adoption studies)…behavioral differences may reveal the contribution of environment to behavior; similarities reveal the contribution of heredity • Adoption studies – kids resemble biological (nature), resemble adoptive family (nurture) Thomas Bouchard study • Found 100 identical twins given up for adoption and raised in different families • Studied hundreds of traits and determined the influence on them (nature vs nurture) • Example – IQ • Correlation coefficient of .69 for identical twins living apart • .88 for identical twins living together • Showed environment has some effect • Living apart was still a moderate-strong correlation – showed IQ heavily influenced by genetics Genetic Concepts • Genome - the entirety of an organism's hereditary information (book) • Chromosome – structure in the nucleus of cells that contains genes determined by DNA sequences. (chapters of the book) • Gene – each DNA segment of a chromosome that determines a trait (words/paragraphs) • DNA (deoxyribonucleic acid) – genetic material that makes up chromosomes (letters) • ** Traits are usually influenced by genes acting together ** Human Cells • 46 chromosomes in 23 pairs – 23 from the sperm of the father – 23 from the egg of the mother • Father contributes a Y sex chromosome (23rd pair), the baby is male; otherwise the baby is female – Males have 44 chromosomes plus X and Y – Females have 44 chromosomes plus X and X • All of the cells of the embryo/baby have the same 23 pairs of chromosomes which carry the genes for the same traits Chromosomal Abnormalities • Occasionally, chromosomes will combine (or fail to) in an unusual way (errors in fertilization) called mutations • Turner’s Syndrome – females with only one X sex chromosome – Shortness, webbed necks, lack ovaries, fail to develop secondary sex characteristics at puberty – Usually normal intelligence – although cognitive deficits in arithmetic, spatial organization, visual perception Chromosomal Abnormalities • Klinefelter’s Syndrome – males with XXY chromosomes • At puberty, male secondary sex characteristics fail to develop, but breast tissue does (minimal sexual development) • Tend to be passive / introversion Chromosomal Abnormalities • Down syndrome – three copies of chromosome-21 • Typically mentally retarded • Have a round head, flat nasal bridge, protruding tongue, small round ears, a fold in the eye lid (far apart), poor muscle tone and coordination, short fingers and toes Genetic Disorders • Genotype – genetic make-up of an individual • Phenotype – the expression of the genes • Gene-environment interaction - term used to describe any phenotypic effects that are due to interactions between the environment and genes Genetic Disorders • Homozygous – Possessing two identical forms of a particular gene, one inherited from each parent (both) / individuals express that phenotypic characteristic • Heterozygous – Possessing two different forms of a particular gene, one inherited from each parent (aka hybrid) • Dominant gene – gene expressed when the genes for a trait are different • Recessive gene – the gene that is hidden or not expressed when the genes for a trait are different • Allele (uh-leel) – a dominant or recessive variant of a particular gene (usually through mutation) • Mutation – random error in gene replication Recessive trait with ONE carrier Recessive trait with TWO carriers Dominant with ONE carrier Dominant with TWO carriers Genetic Disorders • Tay-Sachs syndrome – recessive trait that produces progressive loss of nervous function and death in a baby Genetic Disorders • Albinism – recessive trait that produces a lack of pigment and involves abnormal nerve pathways to the brain resulting in quivering eyes and inability to perceive depth (3D) with both eyes Genetic Disorders • Phenylketonuria (PKU) – recessive trait that results in severe, irreversible brain damage unless the baby is fed a special diet low in phenylalanine within 30 days of birth • Individuals must regulate intake of phenylalanine (artificial sweeteners – aspartame – NutraSweet / Equal) • The infant lacks the enzyme to process this amino acid which can build up and poison the nervous system • Gene-environment interaction Genetic Disorders • Huntington’s disease – dominant gene defect that involves degeneration of the nervous system, characterized by tremors, jerky motions, blindness, and death Genetic Disorders • Sex-linked traits – recessive genes located on the X chromosome with no corresponding gene on the Y chromosome, which results in expression of recessive trait, more frequently in males – Color-blindness – individual cannot see certain colors, most often red and green – Baldness • 25 percent of men begin balding by age 30; two-thirds begin balding by age 60 • There is a 4 in 7 chance of receiving the baldness gene – Hemophilia – long time for blood to clot Genetic Disorders • Alzheimer’s disease – most common form of dementia (loss of cognitive functioning) • A form has been attributed to a gene on chromosome 21, but not in all cases!