Chapter 3 Genes, Environment, and Development Chapter 3 Genes, Environment, and Development

Species Heredity Genetic endowment Human examples Species Heredity Genetic endowment Common to the species Governs maturation and aging Human examples Two eyes, sexual maturity at 12-14 yrs. Natural Selection: Genes allowing adaptation are passed on

Evolution Charles Darwin (1809-1882) Main Arguments 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

Modern Evolutionary Perspectives Modern Evolutionary Perspectives What we do today was adaptive for ancestors Example: mothers invest more in child rearing Maternity is certain; paternity may not be Evolution: gene/environment interaction Traits are demanded by environment Advantageous genes for a particular environment survive

Individual Heredity - The Genetic Code Zygote: union of sperm and egg 23 pairs of chromosomes Each pair influences one characteristic Pair: One from father one from mother Meiosis: produces sperm and ova Mitosis: cell-division process Creates new cells

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

Genes: Their Location and Composition Nucleus Chromosome Gene Cell DNA

Karyotype

Genes: Our Biological Blueprint 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 Genetic Uniqueness & Relatedness Monozygotic (MZ) twins: 100% related 2 genetically identical individuals 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 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

A genotype refers to person’s genetic heritage.

Phenotype The phenotype is one’s genotype expressed in characteristics that can be observed and measured. It includes physical traits (e.g., height, weight) as well as psychological characteristics (intelligence, personality).

Offspring with brown eyes

Sickle-Cell Anemia Caused by hemoglobin S that reduces O2 Caused by hemoglobin S that reduces O2 About 9% affected in U.S. Homozygous recessive (ss) Heterozygous: (Ss) “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 The workings of sex-linked inheritance in red-green color blindness. Figure 3.2

Polygenic Inheritance and Mutations 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 Produces new phenotype Sperm more likely than ova Harmful or beneficial (e.g., sickle-cell protects from malaria)

Errors in chromosome division: Meiosis Errors in chromosome division: Meiosis Too many or too few chromosomes Most spontaneously aborted Down syndrome: Trisomy 21 Physical deformities (eyelid folds, short stubby limbs, thick tongues) Mental retardation 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 The rate of Down syndrome births increases steeply as the mother’s age increases. 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 Leg of X barely connected Sex-linked: affects mostly males eye & vision impairments Hyper-extensible joints (double jointed) elongated face Large testicles (evident after puberty) Flat feet Low muscle tone High arched palate Autism and autistic-like behavior Prominent ears hand biting and hand-flapping Mental Retardation Hyperactivity and short attention span

Genetic Diagnosis and Counseling Genetic Diagnosis and Counseling Tay-Sachs disease Cause: recessive gene pair European Jews/French Canadians Huntington’s Disease Single dominant gene Learn about risk to unborn child Learn about nature, inheritance and effects of genetic disorders in family history

rapid, jerky involuntary movements HUNTINGTON’S DISEASE rapid, jerky involuntary movements difficulty in speaking and swallowing cognitive decline, depression, and occasionally delusions hallucinations and obsessive compulsive disorders.

Behavioral Genetics Genetic/environment cause of trait 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 indicate that activity level, emotion, sex drive may have strong genetic basis Twin, adoption, family studies Reared together or apart Concordance rates

Figure 3.4 Correlations between the traits of identical twins raised apart in the Minnesota Twin Study. Figure 3.4

Estimating Influences 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 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

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 E.g., Sociable genes 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 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 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