Chapter 3 Genes, Environment, and Development

Species HereditySpecies Heredity Genetic endowmentGenetic endowment Common to the speciesCommon to the species Governs maturation and agingGoverns maturation and aging Natural Selection: Genes allowing adaptation are passed onNatural Selection: Genes allowing adaptation are passed on

Evolution Charles Darwin ( )Charles Darwin ( ) Species characteristicsSpecies characteristics How they change over timeHow they change over time Main ArgumentsMain Arguments Genetic variation exists in all speciesGenetic variation exists in all species Some genes aid in adaptationSome genes aid in adaptation Kettlewell’s Moths: Genetic variability provides for adaptationKettlewell’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 © Cengage Learning. All rights reserved.

Genes: Their Location and Composition NucleusChromosomeGene CellDNA

© Cengage Learning. All rights reserved. The Chromosomes

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 Monozygotic (MZ) twins: 100% related Dizygotic (DZ) twins: 50% on average –2–2 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 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.

Epigenetic Effects on Gene Expression Epigenesis –Process through which nature and nurture co- act 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 © Cengage Learning. All rights reserved.

Caused by hemoglobin S that reduces O 2 About 9% affected in U.S. –H–Homozygous recessive (SS) Heterozygous: (AS) “carriers” –C–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 Sickle-Cell Anemia

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 –H–Height, weight, intelligence, temperament Mutations: Change in structure/arrangement of genes –E–Environmental hazards (teratogens) can cause mutations

Down syndrome: Trisomy 21Down syndrome: Trisomy 21 Intellectual disabilitiesIntellectual disabilities Related to age of motherRelated to age of mother

Trisomy 21

Down Syndrome (Trisomy 21) Physical DeformitiesPhysical 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 impairmentsAutism and autistic-like behavior elongated face Large testicles (evident after puberty) Flat feet Low muscle tone Prominent ears hand biting and hand-flapping Mental RetardationHyperactivity 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 © Cengage Learning. All rights reserved.

Behavioral Genetics Genetic/environment cause of trait Heritability estimates (genetic) Methods of studying –E–Experimental and selective breeding – attempt to breed particular traits into animals Tryon’s maze-bright rats –T–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) 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 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 © 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