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Chapter 3 Genes, Environment, and Development • Species Heredity • Genetic endowment • Common to the species • Governs maturation and aging • Natural Selection: Genes allowing adaptation are passed on Evolution • Charles Darwin (1809-1882) • Species characteristics • How they change over time • Main Arguments • Genetic variation exists in all species • Some genes aid in adaptation • Kettlewell’s Moths: Genetic variability provides for adaptation Individual Heredity - The Genetic Code • Zygote: union of sperm and egg – 23 pairs of chromosomes – Pair: One from father one from mother • Meiosis: produces sperm and ova • Mitosis: cell-division process – Creates new cells Mitosis and Meiosis Compared © 2015. Cengage Learning. All rights reserved. Genes: Their Location and Composition Nucleus Cell Chromosome Gene DNA The Chromosomes © 2015. Cengage Learning. All rights reserved. Genes: Our Biological Blueprint Chromosomes threadlike structures made of DNA that contain the genes DNA (deoxyribonucleic acid) contains the genetic information that makes up the chromosomes has two strands-forming a “double helix”-held together by pairs of nucleotides Karyotype Genes: Our Biological Blueprint Genes biochemical units of heredity that make up the chromosomes a segment of DNA synthesizes a protein Genome consisting of all the genetic material in its chromosomes Genetic Uniqueness & Relatedness • Monozygotic (MZ) twins: 100% related • Dizygotic (DZ) twins: 50% on average – 2 ova fertilized by 2 sperm • Siblings: 50% on average • Parent & Child: 50% related, shared • Males: XY; Females: XX Translation of the Genetic Code • Genes provide instructions for development – Eye color and other characteristics – Regulator genes turn on/off gene pairs • Adolescent growth spurt • Shut down some in adulthood Genotype A genotype refers to person’s genetic heritage. Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Epigenetic Effects on Gene Expression • Epigenesis – Process through which nature and nurture coact to bring forth particular developmental outcomes • Epigenetic effects – Environmental factors affect whether or not particular genes in particular cells are expressed – Might explain differences in identical twins © 2015. Cengage Learning. All rights reserved. Sickle-Cell Anemia • Caused by hemoglobin S that reduces O2 • About 9% affected in U.S. – Homozygous recessive (SS) • Heterozygous: (AS) “carriers” – Can transmit gene to offspring Sickle-Cell Anemia • Incomplete dominance – carriers show signs of having recessive trait – Will not have the disease, but sickling episodes • Co-dominance – neither gene in pair is dominant or recessive Sex-Linked Inheritance • Single genes located on sex chromosomes • Actually X-linked • Males have no counterpart on Y chromosome • Females have counter on second X – Requires gene on both X’s for trait • Hemophilia, Colorblindness Figure 3.2 • Polygenic: Most human characteristics influenced by multiple genes – Height, weight, intelligence, temperament • Mutations: Change in structure/arrangement of genes – Environmental hazards (teratogens) can cause mutations • Down syndrome: Trisomy 21 • Intellectual disabilities • Related to age of mother Trisomy 21 Down Syndrome (Trisomy 21) • Physical Deformities flattening of the back of the head slanting of the eyelids short stubby limbs thick tongues Figure 3.3 TURNER SYNDROME (Single X chromosome - XO) 1/3000 females - short stature, sterile, webbed neck, stubby fingers, arms that turn out slightly at the elbow, and a low hairline in the back of the head Klinefelter syndrome: 1/200 males XXY, tall, sterile, feminine traits FRAGILE X SYNDROME Sex-linked: affects mostly males eye & vision impairments elongated face Flat feet Prominent ears Mental Retardation Autism and autistic-like behavior Large testicles (evident after puberty) Low muscle tone hand biting and hand-flapping Hyperactivity and short attention span HUNTINGTON’S DISEASE Single dominant gene on chromosome 4 Rapid, jerky involuntary movements Dementia, cognitive decline, depression, occasional delusions Hallucinations, OCD Tay Sachs disease – chromosome 15 1:30 Ashkenazi Jews carriers Some Genetic Disorders © 2015. Cengage Behavioral Genetics • Genetic/environment cause of trait • Heritability estimates (genetic) • Methods of studying – Experimental and selective breeding – attempt to breed particular traits into animals • Tryon’s maze-bright rats – Twin, adoption, family studies • Reared together or apart • Concordance rates Figure 3.4 Estimating Influences • Genetic similarity – Degree of trait similarity in family members • Shared environmental influences – Living in the same home • Non-shared environmental influences – Unique experiences (e.g., emotionality) Accounting for Individual Differences • Correlations highest in identical twins – Genetic factors determine trait • Correlations higher if twins reared together – Environmental factors • Correlations are not perfect – Non-shared experiences • Identical twins more alike with age Temperament and Personality • Temperament – set of tendencies concerning emotional reactivity, activity, and sociability (genetic) • Temperament correlations • MZ twins = .50 to .60 • DZ twins = 0 • Personality correlations similar • DZ shared environment unimportant • Same home - different personalities • Non-shared environment and genes important Correlations from a Twin Study of the Heritability of Angry Emotionality © 2015. Cengage Learning. All rights reserved. Psychological Disorders • Schizophrenia concordance rates – MZ = 48%: DZ=17% – Affected parent increases risk: 13% • Inherited predisposition – Environmental factors – triggers – Prenatal exposure to infection suspected Gene/Environment Correlations • Passive G/E correlations – parents’ genes influence the environment they provide for children, as well as the genes the child receives • Parents create social home • Evocative G/E correlations – child’s genotype evokes certain reactions • Smiley baby gets more social stimulation • Active G/E correlations – child’s genotype influences the environment that he/she seeks • Child seeks parties, friends, groups, etc. Genetic Influences on Environment • Finding: Parents who read to their children have brighter children. Why? • Environment: reading to child makes them brighter • Genetic: brighter parents more informed or they enjoy reading themselves • Finding: Aggressive children have hostile parents. • Genetic: inherited behaviors • Environment: growing up with negative, hostile parents causes the behavior Controversies Surrounding Genetic Research • Identification of carriers of diseases and disorders • Giving information which leads to abortion • Experimenting with techniques for genetic alteration • Better parenting if child’s genetic predispositions understood