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

Selectionism (Phylogenic & Ontogenic) Requires 3 Mechanisms Variability (Variation) Process for Selection Retention

Phylogenic Selectionism Variability –Mutation –Crossing Over –Random Assortment Process of Selection - Natural Selection Retention - Genes

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 different combinations in gametes Estimated that all the men who ever lived have produced only 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 cm/decade –Age of Menarche

Age of Menarche Norway – Reached at 17 years – Reached at 13 years U. S. – Reached at 14 – Reached at 12-13

Variation in Phenotypes Due to Genotypes Dominant Alleles Recessive Alleles Homozygous Heterozygous Sex-Linked Co-Dominance Incomplete Dominance

Genotype = Both Parents Homozygous Dominant (BRBR - BRBR) Genotype Phenotype BR-BR BROWN All Genotypes are homozygous BRBR All Phenotypes are brown (dominant)

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

Genotype=1 Parent homozygous dominant (BRBR) 1 Parent homozygous recessive (blbl) GenotypePhenotype BRblBrown All genotypes are heterozygous All phenotypes are brown

Genotype= Both Parents Heterozygous (BRbl - BRbl) Both parent phenotypes are Brown GenotypePhenotype 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= ; NS=.24) –(.76 =genotype + Shared Env. + error)

Behavior Results from Interactions (Ross) Genetic Make-Up Interactional History Current Physiological Conditions Current Environmental Conditions Behavioral Dynamics

How Do Genes & Environment 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?