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0. Chapter 3 Genes, Environment, and Development. 0. 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. 0. Evolution.

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Chapter 3 Genes, Environment, and Development

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Chapter 3Genes, Environment, and Development


  • 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



  • 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

  • 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


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

    • 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

  • 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.


  • 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

  • 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

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

    • 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

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 malesXXY, tall, sterile, feminine traits

FRAGILE X SYNDROMELeg of X barely connectedSex-linked: affects mostly males

eye & vision impairmentsHyper-extensible joints (double jointed)

elongated face Large testicles (evident after puberty)

Flat feet Low muscle tone

High arched palateAutism and autistic-like behavior

Prominent ears hand biting and hand-flapping

Mental RetardationHyperactivity and short attention span


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

difficulty in speaking and swallowing

cognitive decline, depression, and occasionally delusions

hallucinations and obsessive compulsive disorders.



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 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


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

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

  • 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

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