Transcript 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” • 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 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 Sex Chromosomes Gene = Location on Chromosome “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 Relative Size of Human Chromosomes Genetic Functions • Mitosis: Cell & Genetic Duplication • Meiosis: Biparental Reproduction Mitosis = Replication Process Genetic Variablity • Random Assortment (Meiosis) • Crossing over (Meiosis) • Mutations (Meiosis or Mitosis) 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 Genetic Variability Crossing Over •Occurs during Meiosis •Occurs prior to gamete formation •Result is “new” chromosome Genetic Variability - Mutation • Error during Mitosis 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 Genotype = Genetic Make-Up • Homozygous – e.g.., BR BR • Heterozygous – e.g.., BR bl • One allele comes from each parent Alleles - Alternate forms of Genes • Produce variability • Dominant Gene (allele) • Recessive Gene (allele) 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 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 Variation in Phenotypes Due to Genotypes •Dominant Alleles •Recessive Alleles •Homozygous •Heterozygous •Sex-Linked •Co-Dominance •Incomplete Dominance Homozygous BRBR) Genotype Dominant (BRBR - Phenotype BR-BR BROWN BR-BR BROWN BR-BR BROWN BR-BR BROWN • All Genotypes are homozygous BRBR • All Phenotypes are brown (dominant) Homozygous recessive (blbl - blbl)Phenotype Genotype blbl blue blbl blue blbl blue blbl blue • All genotypes are homozygous recessive • All phenotypes are blue 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 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 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. 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 Heritability • Genotype • Shared Environmental Effects • Nonshared Environmental Effects • Measurement Error Heritability - Genotype • Monozygotic Twins Identical Genes • Dizygotic Twins - Same as siblings • Siblings - Share parent gene pool • Unrelated children - share broad gene pool Shared Environmental Effects • All persons living in same environment • Generally very low in heritability estimates 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) Interact? Genotype/Environment Effects e.g..., height, weight, muscles, hair color(?), skin color • Passive • Active • Evocative A Behavioral View: Person/Environment Interactions e.g.., clothing, make-up, behavior, skills, hair color? • Passive • Evocative • Active What Canalizes Behavior • Canalization – Increasing restriction of outcome as development proceeds • Genetic Canalization? • Experiential (Environmental) Canalization?