The Human Heritage: Genes and the Environment

1. The Human Heritage:Genes and the Environment

2. 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

3. 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

5. 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

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

8. 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

10. 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

11. 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

12. Not Exactly Identical

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

14. 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

15. Codominance: Result is distinct characteristics

16. Genetic Sex also Source of Variability

17. 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

18. 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

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

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

21. 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?

22. 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

23. 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.

24. 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

25. 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

26. 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

27. 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

28. 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%

29. 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)

31. 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

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

34. 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

36. 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

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

38. 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