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 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?

The Simple View Behavior = genes + environment The Realistic View Behavior = genes + prenatal environment + parental influence + nutrition + family income + education + culture + traumas + chance …

Genetics and Behavior NucleusChromosomeGene CellDNA

Genotype & Phenotype

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

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

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.

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

- 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 Sickle Cell Disease and Malaria

Sexual Reproduction Combines gametes thereby creating new genotype May have evolved to outcompete parasites

Genes Affect Behavior Behavioral Genetics Methods: –Twin Studies Compare MZ and DZ Twins: –Adoption Studies:

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 Identical twins Fraternal twins Same sex only Same or opposite sex

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 Nature v Nurture: Twin Studies

Jack Yufe: raised by Jewish father in Caribbean Oskar Stohr: raised by catholic grandmother in Nazi Germany Nature v Nurture: Twin Studies 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.

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

MZ and DZ concordance rates

Separated Twins

Twins Studies Comparing identical twins separated at birth Twins studies movie

Environmental Influences Prenatal environment

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.

Child Maltreatment, Criminality, and Gene Expression

Temperament and genetics 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?

Behavior Genetics 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