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Chapter 3

Chapter 3 . Behavior Genetics. The Human Genome . Genetic Roadmap Entire genetic code of the human species. Genetic Structures. DNA - Dioxyribonucleic Acid Genetic Code Genetic Alphabet = 4 Letters A: Adenine C: Cytosine G: Guanine T: Thymine. Genetic “Words”.

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Chapter 3

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  1. Chapter 3 Behavior Genetics

  2. The Human Genome • Genetic Roadmap • Entire genetic code of the human species

  3. Genetic Structures • DNA - Dioxyribonucleic Acid • Genetic Code • Genetic Alphabet = 4 Letters • A: Adenine • C: Cytosine • G: Guanine • T: Thymine

  4. Genetic “Words” • Made up of two strands of DNA molecules • Infinite in length (e.g.. ACGCTCTCGA) • Because DNA is a Double Helix exact replication is possible • Mutations result when “proofreading fails

  5. Chromosome • Continuous Strands of DNA • Locations which have functions are Genes • 46 Chromosomes in humans • Located as 23 Pairs • 22 Pairs are Autosomes • 1 Pair are SexChromosomes

  6. Gene = Location on Chromosome

  7. “Parsimony” of Genetics • 4 Bases (ACGT) produce enormous diversity • Length & uniqueness of ACTG which produces diversity • Double helix of DNA allows exact replication during Mitosis • Errors in mitosis allows further variability

  8. Relative Size of Human Chromosomes

  9. Genetic Functions • Mitosis: Cell & Genetic Duplication • Meiosis: Biparental Reproduction

  10. Mitosis = Replication Process

  11. Genetic Variablity • Random Assortment (Meiosis) • Crossing over (Meiosis) • Mutations (Meiosis or Mitosis)

  12. Random Assortment • Occurs during later stage of Meiosis, as gametes are being formed • Pairs of chromosomes go to opposite ends of cell • 1/2 of chromosomes (1 from each pair) go to new cell (gamete) • Which individual of pair is random • Produces 1 in 64 trillion chance of duplication • This is multiplied by incalculable effects of mutation & crossing-over

  13. Genetic VariabilityCrossing Over • Occurs during Meiosis • Occurs prior to gamete formation • Result is “new” chromosome

  14. Genetic Variability - Mutation • Error during Mitosis

  15. Genetic Variability -Bisexual Reproduction • Estimated that each human has the capacity to produce 103000 different combinations in gametes • Estimated that all the men who ever lived have produced only 1024 sperm • Extremely unlikely that there has ever been a genetic duplicate • Exception - Identical (Monozygotic) Twins

  16. Genotype = Genetic Make-Up • Homozygous • e.g.., BR BR • Heterozygous • e.g.., BR bl • One allele comes from each parent

  17. Alleles - Alternate forms of Genes • Produce variability • Dominant Gene (allele) • Recessive Gene (allele)

  18. Phenotype - Expression of Characteristics • Expression of • Genotype • Environment • Transaction • Examples- • Down Syndrome (Life expectancy of 12) • Height - since 1900-1 cm/decade • Age of Menarche

  19. Age of Menarche • Norway • 1840 - Reached at 17 years • 1990 - Reached at 13 years • U. S. • 1890 - Reached at 14 • 1990 - Reached at 12-13

  20. Variation in PhenotypesDue to Genotypes • Dominant Alleles • Recessive Alleles • Homozygous • Heterozygous • Sex-Linked • Co-Dominance • Incomplete Dominance

  21. Genotype = Both Parents Homozygous Dominant (BRBR - BRBR) GenotypePhenotype BR-BR BROWN BR-BR BROWN BR-BR BROWN BR-BR BROWN • All Genotypes are homozygous BRBR • All Phenotypes are brown (dominant)

  22. Genotype=Parents Homozygous recessive (blbl - blbl) Genotype Phenotype blbl blue blbl blue blbl blue blbl blue • All genotypes are homozygous recessive • All phenotypes are blue

  23. Genotype=1 Parent homozygous dominant (BRBR) 1 Parent homozygous recessive (blbl) Genotype Phenotype BRbl Brown BRbl Brown BRbl Brown BRbl Brown • All genotypes are heterozygous • All phenotypes are brown

  24. Genotype= Both Parents Heterozygous (BRbl - BRbl) • Both parent phenotypes are Brown Genotype Phenotype BRBR (Homozygous) Brown BRbl (Heterozygous) Brown blBR (Heterozygous) Brown blbl (Homozygous) blue • 3-in-4 chances phenotype will be Brown • 1-in-4 chance phenotype will be blue • How generation can be skipped

  25. Sex-Linked Characteristics • Characteristic is recessive • Location is on the Y chromosome • Male who inherits that recessive (MPB) has no dominant to mask recessive • Female who inherits that recessive is likely to have a dominant on other Y • These females are “carriers” who may pass Y based recessive to son.

  26. Forget It! • Human behavior is not single gene • Mostly polygenic • Genes do not directly produce behavior • Genes work through the structures they enable • Human Behavior is multifactorial

  27. Heritability • Genotype • Shared Environmental Effects • Nonshared Environmental Effects • Measurement Error

  28. Heritability - Genotype • Monozygotic Twins - Identical Genes • Dizygotic Twins - Same as siblings • Siblings - Share parent gene pool • Unrelated children - share broad gene pool

  29. Shared Environmental Effects • All persons living in same environment • Generally very low in heritability estimates

  30. Nonshared Environmental Effects • Effect on individual • No 2 persons (even living together in same house) have same environment • Determined by subtracting out Monozygotic twins living in same living situation (e.g..., NS=1.00-.76; NS=.24) • (.76 =genotype + Shared Env. + error)

  31. How Do Genes & Environment Interact?Genotype/Environment Effects e.g..., height, weight, muscles, hair color(?), skin color • Passive • Active • Evocative

  32. A Behavioral View: Person/Environment Interactions e.g.., clothing, make-up, behavior, skills, hair color? • Passive • Evocative • Active

  33. What Canalizes Behavior • Canalization – Increasing restriction of outcome as development proceeds • Genetic Canalization? • Experiential (Environmental) Canalization?

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