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Download Genetics and Behavior Principles of Gene Action and Heredity
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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 – 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 Identical twins raised together Same sex twins raised together Diff sex twins raised together Siblings Unrelated siblings .72 .86 .62 .57 .47 .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 Fraternal twins Siblings Half-sibling Fisrt cousin Child of two sch. Parents Child of one sch. Parent 48% concordance 17% 9% 6% 2% 46% 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