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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 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


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


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
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 our biological blueprint1
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


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.

  • 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
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 anemia1
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


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
polygenic inheritance and mutations
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
down syndrome 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
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

fragile x syndrome leg of x barely connected sex linked affects mostly males
FRAGILE X SYNDROMELeg of X barely connectedSex-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
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


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


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 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
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


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