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Genetics. The Nature/Nurture Debate. How great is the influence of genes or environment on our behavior, personality, biology, etc.? . The Nature Nurture Debate. Make two columns on a sheet of paper - 1) nature; 2) nurture

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The Nature/Nurture Debate

  • How great is the influence of genes or environment on our behavior, personality, biology, etc.?


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The Nature Nurture Debate

  • Make two columns on a sheet of paper - 1) nature; 2) nurture

  • Write characteristics you believe are mostly nature or mostly nurture in the appropriate column

  • If the characteristic was nurture, what seemed to be the influences?


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The Simple View

  • Behavior = genes + environment

    The Realistic View

  • Behavior = genes + prenatal environment + parental influence + nutrition + family income + education + culture + traumas + chance …


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Nucleus

Chromosome

Gene

Cell

DNA

Genetics and Behavior



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Genes: Essential Definitions

  • Chromosomes

    • threadlike structures made of DNA that contain the genes

  • DNA (deoxyribonucleic acid)

    • complex molecule containing the genetic information that makes up the chromosomes

    • has two strands-forming a “double helix”- held together by bonds between pairs of nucleotides


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Genes: Essential Definitions

  • Genes

    • biochemical units of heredity that make up the chromosomes

    • a segment of DNA capable of synthesizing a protein

    • The paradox 30,000 genes for 300,000 proteins

  • Genome

    • the complete instructions for making an organism

    • consisting of all the genetic material in its chromosomes


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Genes: Essential Definitions

  • Genotype

    -The genetic constitution of an individual. Depending on context, this may refer to the alleles at a single locus or to the complete set of genes.

  • Phenotype

    -Any measurable trait of an individual. Phenotype results from an interaction between genotype and environment.


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Genotypic Variation Is Created by Sexual Reproduction

  • What determines the genetic uniqueness of individuals?

    • Gametes

    • Zygote

  • Mutations are experiments in selective advantage

    • Industrial melanism

    • Sickle-cell disease


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Sickle Cell Disease and Malaria

  • - homozygotes

    • anemia, joint pain, swollen spleen, frequent severe infections, high rate of childhood death

  • - heterozygotes

  • - basically normal blood function

  • - resistant to malaria

  • Price for malarial resistance

  • - homozygous sickle cell children


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Sexual Reproduction

  • Combines gametes thereby creating new genotype

  • May have evolved to outcompete parasites


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Genes Affect Behavior

  • Behavioral Genetics Methods:

    • Twin Studies Compare MZ and DZ Twins:

    • Adoption Studies:


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Identical

twins

Fraternal

twins

Same

sex only

Same or

opposite sex

Behavior Genetics

  • Identical Twins

    • develop from a single zygote (fertilized egg) that splits in two, creating two genetic replicas

  • Fraternal Twins

    • develop from separate zygotes

    • genetically no closer than brothers and sisters, but they share the fetal environment


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Nature v Nurture: Twin Studies

Identical (monozygotic twins)

Non-identical, fraternal (dizygotic twins)

Identical twins reared together

same genes (relatedness of 1.0)

same environment

Identical twins reared apart

sane genes (relatedness of 1.0)

different environment

Fraternal twins reared together

half genes the same (relatedness 0.5)

same environment

Fraternal twins reared apart

half genes the same (relatedness 0.5)

different environment


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Nature v Nurture: Twin Studies

Oskar Stohr: raised by catholic grandmother in Nazi Germany

Jack Yufe: raised by Jewish father in Caribbean

If we had identical twins reared apart could we separate the effects of phenotype, of genotype, and of the environment. In some cases this has happened.


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Nature v Nurture: Twin Studies

Both like sweet liqueurs

Store rubber bands on their wrists

Read magazines from back to front

Dip buttered toast in their coffee

Have very similar personalities




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Twins Studies

  • Comparing identical twins separated at birth

  • Twins studies movie


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Environmental Influences

  • Prenatal environment


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Social and Environmental Contexts Influence Genetic Expression

  • African Americans and Hypertension: a controversial theory

  • Gene expression as concerns child maltreatment and criminality is reflected in next slide.


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Child Maltreatment, Criminality, Expression

and Gene Expression


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Temperament and genetics Expression

  • Suomi genetic studies on rhesus monkeys

    • Two alleles of one gene:

      • the “short” version causes neurobehavioral deficits ONLY IF the infant monkey is raised with peers but without its mother

      • The “long” version causes no neurobehavioral deficits, regardless of rearing

    • Maternal buffering?


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Behavior Genetics Expression

  • Adoption studies

    • Are adopted kids more like their biological relatives or their adopted relatives?

    • General findings: adoptees more like biological parents than adopted parents in intelligence and personality/temperament