1 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3:...

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Carol K. Sigelman, Elizabeth A. Rider

Life-Span Human Development, 4th Edition

Chapter 3: Genes, Environment, and Development

Chapter 3

Nature-Nurture

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Species Heredity

• Genetic endowment

- Species have in common

- Govern maturation and aging processes.

• Examples in humans

- 2 eyes, mature sexually at age 12 to 14

• Evolved through natural selection

- Genes allowing species to adapt passed on

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Evolution

• Charles Darwin (1809-1882)

- How characteristics of a species change over time

- How new species can evolve from earlier ones

• Main arguments

- There is genetic variation in a species

- Some genes aid in adaptation more than others

• Kettlewell’s moths (1959): Genetic variability

allows adaptation

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Modern Evolutionary Perspectives

• How what we do today was adaptive for ancestors.

- Ethology: Evolution of behavior in natural environments

- Developmental psychobiology: Biology & environment

• Example: Mothers (~all mammals) invest more than fathers in childrearing - maternity certain

- Adaptive mammalian male reproductive strategies

- Invest energy in few offspring – paternity certain

- Multiple partners/small investment – paternity uncertain

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Translation of the Genetic Code• Genes provide instructions for development of various

characteristics.- Example: Eye color, or the development of neurons

• Specific gene pairs turned on or off by regulator genes at different times.

- Regulator genes responsible for adolescent growth

- Same genes shut down the action in adulthood

• Genotype: Inherited genetic makeup (genetic potential for tallness)

• Phenotype: The characteristic/trait expressed (actual height)

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Mechanisms of Inheritance

• Single Gene-Pair Inheritance

- Dominant Genes: Dominant trait

- Recessive Genes:

- Recessive trait if paired with a similar gene

- Trait not produced if paired with a dominant gene

- Recessive Traits: Homozygous recessive genes.

- Dominant Traits: Dominant hetero-or homozygous

gene pair

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Single Gene-Pair Inheritance: Sickle-Cell Disease

• About 9% of Americans affected

- Homozygous recessive

• Heterozygous: Carriers

- Can transmit gene to offspring

- If both parents carriers: 25% chance

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Mechanisms of Inheritance: Sex-Linked Inheritance

• Single genes located on sex chromosomes

• Actually X-linked

• Males have no counterpart on Y chromosome

• Females have counterpart on second X

chromosome

- Requires gene on both X’s for trait

• Hemophilia, Colorblindness, Duchene MD

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Mechanisms of Inheritance: Polygenic Inheritance

• Most important human characteristics

- Height, weight, intelligence, temperament,

personality, sexual orientation, etc.

• Multiple (100s, 1000s) pairs of genes

- ~infinite combinations of genes leads to…

• Normally distribution of these characteristics

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Alternative Mechanisms of Inheritance: Mutations

• A change in structure/arrangement

• Produces a new phenotype

• Sperm more likely than ova

• May be harmful or beneficial

- Sickle-cell gene prevents malaria

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Chromosome Abnormalities

• Errors in chromosome division during meiosis

- Too many or too few chromosomes

• Most spontaneously aborted

• Down Syndrome: Trisomy 21

- Physical deformities

- Mental retardation

- Related to age of parents

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Behavioral Genetics

• Genetic/environmental cause of traits

• Heritability estimates (population estimates)

- % of variability in characteristic due to genetic var

• Experimental and selective breeding

- Tryon’s maze-bright rats

• Twin, adoption, family studies

- Reared together or apart

- Concordance rates

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Behavioral Genetics

• Studies reveal substantial heritability for many physiological, psychological and behavioral traits

- MZ correlations higher than DZ correlations

- Similar for reared together & apart

- Correlations higher for biological relatives than for (adopted) family members

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Figure 3.4

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Behavioral Genetics

• DZ correlations typically less than 1.0

• Identical twins more alike with age

• Correlations higher if twins reared together

- Suggests that environment also plays a role

- Multiple types of environmental influence possible

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Estimating Influences

• Genetic similarity

- Degree of genotype similarity

• Shared environmental influences

- Living in the same home, same parents, etc.

• Non-shared environmental influences

- Unique experiences

- Youngest v. oldest child, Parental favorite, etc.

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Estimating Influences

• Similar environments & experiences have

little impact & do not make us more alike

- Shared genes (NOT shared environ)

make us similar

- Non-shared environment makes us

different

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Individual Differences in Personality

• 40% genetic

• 40% environment (+ 20% error)

- Shared: 5%

- Non-shared: 35%

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Temperament and Personality

• Temperament correlations

- Identical Twins: .50-.60

- Fraternal Twins: 0

• Personality correlations similar

- Shared environment unimportant

- Non shared environment and genes important

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Nature & Nurture

• Reciprocal determinism- Heritability < 1.0 revealing environmental influence

- Environmental influence interacts w/ genes in development

- Genes -> environment -> genes & development

- Ex: genetic potential for intelligence interacts w/ enriched environment

- Genotype v. phenotype

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Figure 3.5

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Ex: Sociable genes

• Passive:- Inherited genes + parents

create social environment

• Evocative- Smiley baby gets more

social stimulation

- Non-shared

• Active- Sociable child seeks social

activities

- Non-shared

Gene/Environment Interactions (correlations)

• Passive:- Inherited genes +

parents create environ consistent w/ genes

• Evocative- Genetically influenced

temperament evokes different responses

• Active- Seek experiences

consistent with genes

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