The Human Heritage: Genes and the Environment

Nature/Nurture First coined by Richard Mulcaster (1582) Refers to the ‘twin forces on development’ Biological and environmental influences Nature Inborn biological endowment Nurture environment within which development occurs Interaction of Forces

Sexual Reproduction and Genetic Transmission Chromosomes Single molecule of DNA, thousands of genes 23 + 23 = zygote Genes segments of DNA, double helix, ladderlike blueprint for synthesis of protein molecule units of heredity

Sexual Reproduction and Patterns of Heredity The basics somatic cells hold genetic info on copies of 46 chromosomes inherited at conception Chromosomes dispersed throughout the nucleus 23 pairs of chromosomes 22 autosomes, 1 sex chromosome males xy females xx

Cell Division: Somatic Cells Mitosis for somatic (body) cells each cell replicates itself, then divides result is two cells identical to original

Cell Division: Germ Cells Meiosis for germ cells replication with 3 processes to ensure resulting cell is nonidentical to germ cells (genetic diversity: chances are 1/70 trillion) 2 steps of division crossing over random pairing during 2nd division monozygotic vs. dizygotic twins

Genotype/Phenotype Genotype Phenotype the set of genes you inherit, your unique blueprint Phenotype how that set of genes is expressed as a result of the environmental stresses the observable characteristics

Environment Genetic code is expressed in environments Multi-levels of influence possible (egs.) prenatal hormonal environment chemical environment of the cell nutrition of mother during pregnancy stress of mother opportunity for physical exercise birth order as it relates to attention from parent

Not Exactly Identical

Mendel’s Laws of Inheritance Definitions of terms locus homozygous heterozygous allele dominant recessive intermediate expression of trait

Laws of Inheritance Discrete traits inherited on the basis of allele information from a single locus Chin cleft Blood type Polygenetic traits inherited as result of information from several genes Verbal skill shyness

Codominance: Result is distinct characteristics

Genetic Sex also Source of Variability

Sex Linked Genetic Effects: Red/Green Colorblindness recessive trait chances are 1/10 for males chances are 1/100 for females gene carried on x chrom, males have no complementary allele to compensate for the harmful effects

Gene-Environment Interactions Behavioral geneticists study how genes and environment combine to influence organism’s development Variations in environment can have large effects on development of phenotype Gene-environment interaction is a two-way process Genetic factors play a role in the environments that individuals inhabit and how they shape their environments

Range of Reaction: charting the change in phenotype as environment changes

Canalization: some characteristics restricted to narrow range despite wide variation in environment

Heritability: The study of genetic influences on behavior Attempt to assess the degree to which variation among individuals on a given trait can be attributed to genetic as compared to environmental differences e.g., weight - a physical trait e.g., intelligence - a psychological trait can factors in the environment influence weight or intelligence?

Heritability, cont’d Degree to which variation among individuals on a particular trait can be attributed to genetic differences h2 = variation due to genes total variation applies to groups and not to individuals for clones, any variation has to be due to environment, thus h2=0 h2=1- variance accounted for by environment heritability increases as genetic diversity increases and decreases as genetic diversity decreases

Heritability: Infant Temperament This video from the laboratory of Hill Goldsmith shows part of a study about infant temperament. An object of desire is set in motion, first for each infant in a pair of fraternal twins and then for each infant in a pair of identical twins. Note how the twins react when prevented from reaching the desired object.

Heritability of Intelligence: History Francis Galton’s Eminent Persons Study tested idea that differences in intellectual achievement was due to genetic differences basic flaw in logic is that eminent people also shared similar environment as well as gene pool first to use adoptive method in study of boys adopted by RC Popes; found little evidence that environment affected eminence Recommendations made for selective breeding, as they were to be made later by Hitler Interesting aside: Darwin’s cousin

Heritability of Intelligence: Kinship Studies Twin Methods correlations among IQs of pairs of people related to different degrees, e.g., identical twins, dizygotic twins, siblings, Adoptive Methods correlations among pairs of people who share an environment but not genes, e.g., adopted child and biological child

Intelligence: The Findings Identical twins raised apart .72 Identical twins raised together .86 Same sex twins raised together .62 Diff sex twins raised together .57 Siblings .47 Unrelated siblings .30

Heritability of Schizophrenia Adoption Studies e.g., Kety et al (1976) found strong evidence of heritability only biological relatives of adoptee who is schizophrenic show high incidence of schizophrenia

Heritablity of Schizophrenia Twin Studies High concordance for identical twins, this concordance deceases as genetic relatedness decreases Identical twins 48% concordance Fraternal twins 17% Siblings 9% Half-sibling 6% Fisrt cousin 2% Child of two sch. Parents 46% Child of one sch. Parent 13%

Mutations and Genetic Abnormalities Mutations are errors in the process of gene replication; can be positive but usually negative Down Syndrome (chromosomal error) Phenylketonuria (PKU- defective recessive gene) Klinefelter syndrome (sex-linked chromosomal abnormality) Sickle-cell anemia (recessive gene)

Chromosomal Errors Most incompatible with survival Variations in number sex chromosomes Turner’s XO Klinefelter’s XXY XYY Variations in number of other chromosomes Down’s Syndrome, Trisomy 21 Edward’s Syndrome; Trisomy 17

PKU Recessive gene disorder causes excessive buildup of phenylalaline causing brain damage environmental intervention (diet) can reduce effects

Huntington’s Disease dominant gene disorder 50% chance of offspring inherit the disorder 1/15,000 incidence charcterized by severe mental and physical disorder lag in onset of symptoms (35-45 yrs) accounts for continued occurrence can be detected through genetic testing

Biology and Culture Cultural evolution can also account for existence of skills in a population Innovations passed onto succeeding generations Through processes of direct instruction, language, and demonstration Little evidence of cultural evolution in other species Meme: basic unit of cultural evolution

Cultural and Survival Some cultural tools may ensure survival Hunting, gathering methods Language Child rearing practices (Quechuan babies)

Coevolution Two forms of evolution (cultural and biological) influence each other Evidence that culture has influenced biology through the impact it has on reproductive advantage (e.g., tool use) The problems of sorting out the nature-nurture influence