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  • 1. Psychology 372 Behavioural Genetics
  • 2. Behavioural Genetics <ul><li>Studies the role of genetics and environment in animal behaviour </li></ul><ul><li>Intersects with psychology in general (especially developmental, abnormal), human behavioural ecology, evolutionary psychology, genetics, population genetics </li></ul><ul><li>Actually, an older field than psychology </li></ul>
  • 3. Sir Francis Galton <ul><li>Hereditary Genius (1869) </li></ul><ul><ul><li>“… a man’s natural abilities are derived by inheritance, under exactly the same limitations as are the form and physical features of the whole organic world.” </li></ul></ul><ul><li>Rather overstated things, but was the beginning of behavioural genetics </li></ul><ul><li>Family and twin study designs </li></ul><ul><li>Correlations and regressions </li></ul><ul><li>Both shared genes and shared environment important </li></ul>Galton at age 50 <www.galton.org/>
  • 4. Early Behavioural Genetics <ul><li>Traditionally, studied inheritance of behavioural traits </li></ul><ul><li>Demonstrate genetic influence on behaviour exist </li></ul><ul><li>Conflict with Behaviorism </li></ul>
  • 5. Behaviorism <ul><li>John B. Watson </li></ul><ul><li>“ Hard-line” Behaviorism </li></ul><ul><ul><li>“ Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select - doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors.” </li></ul></ul><ul><li>Predominant in psychology and social sciences until 1960s </li></ul><ul><li>Environmental control over behaviour with no or minimal genetic influence </li></ul>
  • 6. Nature and Nurture <ul><li>Back to 17th century philosophy </li></ul><ul><li>Empiricism </li></ul><ul><ul><li>Tabula rasa </li></ul></ul><ul><li>Nativism </li></ul>
  • 7. Determinism <ul><li>Genetic determinism </li></ul><ul><li>Genetic predispositions </li></ul>
  • 8. Contributing Factors <ul><li>Now seen more as nature via nurture </li></ul><ul><li>Nature </li></ul><ul><ul><li>The genes </li></ul></ul><ul><li>Nurture </li></ul><ul><ul><li>Shared environment </li></ul></ul><ul><ul><li>Unique/non-shared environment </li></ul></ul>
  • 9. Heritability Estimates <ul><li>Trait 1: low heritability, high shared environment </li></ul><ul><li>Trait 2: high heritability </li></ul><ul><li>Trait 3: low heritability, low shared environment, high unique environment </li></ul>1.0 0.8 0.6 0.4 0.2 0 Trait 1 Trait 2 Trait 3 Correlation Correlation of Sibling Traits in Shared Family Environment Monozygous twins Biological siblings Adoptive siblings
  • 10. More Recent Trends <ul><li>Shift from study of inheritance </li></ul><ul><li>Use of quantitative methods </li></ul><ul><ul><li>Estimates degree to which differences in individuals are due to genetic and environmental differences; doesn’t specify gene or environmental factors </li></ul></ul><ul><li>Molecular genetics </li></ul><ul><ul><li>Identification of specific genes for behaviours </li></ul></ul><ul><li>Study of quantitative trait loci (QTLs) </li></ul>
  • 11. Genetic Components <ul><li>We’ll get to the behaviours </li></ul><ul><li>Need a basic familiarity with genetic terminology and elements </li></ul>
  • 12. Terms <ul><li>Gene </li></ul><ul><ul><li>Smallest discrete inherited unit </li></ul></ul><ul><li>Allele </li></ul><ul><ul><li>Different forms of specific gene </li></ul></ul><ul><li>Two alleles of each gene </li></ul><ul><ul><li>Homozygous or heterozygous </li></ul></ul><ul><li>Alleles can be dominant or recessive </li></ul><ul><li>Genotype and phenotype </li></ul>
  • 13. Punnett Squares <ul><li>Standard is to use capitals for dominant, lower-case for recessive </li></ul><ul><li>Will produce all the possible genotypic outcomes </li></ul><ul><li>Assumes genes are independent of each other </li></ul><ul><li>Punnett Square Calculator </li></ul>
  • 14. Chromosomes <ul><li>23 pairs of chromosomes in humans </li></ul><ul><ul><li>22 autosomal, 1 sex </li></ul></ul><ul><li>Loci (locus, singular) of gene(s) </li></ul><encarta.msn.com/media_461543483/Human_Male_Karyotype.html> <adapted from: www.accessexcellence.org/ RC/VL/GG/human.php>
  • 15. Meiosis and Mitosis <ul><li>Mitosis </li></ul><ul><ul><li>Non-gamete cell division </li></ul></ul><ul><ul><li>Mitosis animation </li></ul></ul><ul><li>Meiosis </li></ul><ul><ul><li>Production of gametes </li></ul></ul><ul><ul><li>Meiosis animation </li></ul></ul>
  • 16. Gregor Mendel <ul><li>Augustinian priest </li></ul><ul><ul><li>Well trained in mathematics, physics, biology </li></ul></ul><ul><li>From 1856-1863 cultivated and tested 29,000 pea plants </li></ul><ul><li>Sought to understand variation </li></ul><ul><li>Work published in 1866, but largely ignored until rediscovered in 1900 </li></ul><ul><li>Two laws of heredity </li></ul><en.wikipedia.org/wiki/Image:Mendel.png>
  • 17. Mendel’s First Law of Heredity <ul><li>Law of Segregation </li></ul><ul><li>Genes “segregate” during gamete formation </li></ul><ul><ul><li>Offspring receive one gene from each parent </li></ul></ul><ul><li>Dominant and recessive forms </li></ul>
  • 18. Mendel’s Second Law of Heredity <ul><li>Law of Independent Assortment </li></ul><ul><ul><li>Inheritance of one gene is not affected by the inheritance of another gene </li></ul></ul><ul><li>Does get violated in various situations </li></ul><ul><ul><li>Linkage based on proximity of loci on chromosome </li></ul></ul><ul><ul><li>Recombination (chromosomal crossovers) </li></ul></ul><ul><ul><li>Recombination between linked genes animation </li></ul></ul>
  • 19. Hardy-Weinberg Equilibrium <ul><li>Frequencies of alleles and genotypes don’t change across generations unless forces (e.g., natural selection, migration, etc.) alter them </li></ul><ul><li>For a population, can calculate allele and genotype frequencies, assuming random mating </li></ul>
  • 20. Frequencies <ul><li>Consider a single locus with two alleles </li></ul><ul><li>Dominant A and recessive a </li></ul><ul><li>Frequency(A) = p </li></ul><ul><li>Frequency(a) = q </li></ul><ul><li>Expected genotype frequencies are the product of the mother’s (p + q) and father’s alleles (p + q) </li></ul><ul><li>Thus, (p + q) 2 = p 2 + 2pq + q 2 </li></ul>
  • 21. Punnett Square and Hardy-Weinberg A a A a p = 0.6 q = 0.4 p = 0.6 q = 0.4 Sperm Eggs AA (p 2 ) 0.6x0.6 = 0.36 Aa (pq) 0.6x0.4 = 0.24 aa (q 2 ) 0.4x0.4 = 0.16 Aa (pq) 0.6x0.4 = 0.24 (p + q) 2 = 1 p 2 + 2pq + q 2 = 1
  • 22. Example <ul><li>1 in 1700 US Caucasian newborns have cystic fibrosis </li></ul><ul><ul><li>C for normal is dominant over c for cystic fibrosis </li></ul></ul><ul><li>What percentage of the population have cystic fibrosis? </li></ul><ul><ul><li>Genotype cc is q 2 , so: </li></ul></ul><ul><ul><li>q 2 = 1/1700 = 0.00059 = 0.059% </li></ul></ul>
  • 23. Allele Frequencies <ul><li>Then the frequency of the c allele is </li></ul><ul><ul><li>c = q = square root of 0.00059 = 0.024, or 2.4% </li></ul></ul><ul><li>Now, to find the frequency of C, </li></ul><ul><ul><li>C = p = (1 - q) = 1 - 0.024 = 0.976, or 97.6% </li></ul></ul>
  • 24. Genotype Frequencies <ul><li>Frequency of homozygous dominants (CC) </li></ul><ul><ul><li>p 2 = 0.976 2 = 0.953, or 95.3% </li></ul></ul><ul><li>Frequency of heterozygous condition (Cc) </li></ul><ul><ul><li>2pq = 2(0.976 x 0.024) = 0.0468, or 4.68% </li></ul></ul><ul><li>Thus, out of 1700 people, 1620 are homozygous dominant (CC), 79 are heterozygous carriers (Cc), and 1 is homozygous recessive (cc) </li></ul>
  • 25. Autosomal Chromosomes <ul><li>In humans, 22 autosomal chromosomes </li></ul><ul><li>All chromosomes have a short (p) and long (q) arm </li></ul><ul><li>When stained, distinct “bands” appear on the chromosome </li></ul><ul><li>Locations of genes identified by the chromosome number, the arm, the region, and then the band </li></ul><ul><ul><li>E.g., 5p14 is chromosome 5, arm p, region 1, band 4 </li></ul></ul>p arm q arm Chromosome 5
  • 26. Sex Chromosomes <ul><li>Two chromosomes that differ for males and females </li></ul><ul><li>XX and XY </li></ul><ul><li>S ex-determining r egion Y (SRY) </li></ul><ul><ul><li>Gene located on short arm of Y chromosome </li></ul></ul><ul><ul><li>Master switch triggering events converting the embryo into a male; without the gene, embryo is female </li></ul></ul><ul><ul><li>Evidence: aneuploid humans with karyotypes XXY, XXXY, even XXXXY are all functionally male </li></ul></ul><ul><ul><li>SRY transgenic XX karyotype mice </li></ul></ul><http://users.rcn.com/jkimball.ma.ultranet /BiologyPages/S/SexChromosomes.html>
  • 27. Sex Linked Genes <ul><li>X chromosome carries hundreds of genes </li></ul><ul><li>Few have anything to do directly with sex </li></ul><ul><li>Special rules of inheritance because </li></ul><ul><ul><li>Males have only single X chromosome </li></ul></ul><ul><ul><li>Almost all genes on X have no counterpart on Y, thus </li></ul></ul><ul><ul><li>Any gene on X, even if recessive in females, will be expressed in males </li></ul></ul><ul><li>Genes inherited in this fashion are called sex-linked, or X-linked </li></ul>
  • 28. Hemophilia Example <ul><li>Blood clotting disorder </li></ul><ul><ul><li>Mutant gene encoding clotting factor VIII on X chromosome </li></ul></ul><ul><li>With only one X chromosome, males who inherit defective gene from their mother are unable to produce factor VIII and are hemophiliacs </li></ul><ul><li>For heterozygous female carriers, the normal copy of the gene provides the needed factor VIII </li></ul>
  • 29. More Exceptions to Mendel’s Laws <ul><li>Mutations </li></ul><ul><li>Chromosomal errors </li></ul><ul><li>Repeat sequences </li></ul><ul><li>Genomic imprinting </li></ul>
  • 30. Mutations <ul><li>Many genetic diseases involve spontaneous mutations </li></ul><ul><li>Majority of mutations do nothing </li></ul><ul><li>Of those that do something, practically all are “bad” (i.e., create a disfunction from “normal”) </li></ul><ul><li>Only very, very occasionally does a mutation confer a benefit to the individual </li></ul><ul><li>We’ll come back to mutations in chapter 4 </li></ul>
  • 31. Chromosomal Errors <ul><li>Nondisjunction </li></ul><ul><ul><li>Failure to apportion chromosomes equally during meiosis </li></ul></ul><ul><ul><li>Generally leads to spontaneous abortion in first few weeks post conception </li></ul></ul><ul><li>Down syndrome </li></ul><ul><ul><li>Three copies (trisomy) of chromosome 21 (one of the smallest chromosomes) </li></ul></ul><ul><li>Monosomy (one copy) of a chromosome seems to always be fatal (would be missing essential genes) </li></ul>
  • 32. Repeat Sequences of DNA <ul><li>1 to 4 nucleotide bases repeat up to a few dozen times </li></ul><ul><ul><li>Don’t really know why these repeats occur </li></ul></ul><ul><ul><li>Common and normal; perhaps up to 50,000 places in human genome </li></ul></ul><ul><li>Problem when number of repeats at a particular loci increase beyond normal range </li></ul>
  • 33. Example: Huntington’s Disease <ul><li>Repeat of three bases (triplet repeat) on chromosome 4 </li></ul><ul><li>Normal (non-Huntington’s) people have 11-34 copies of triplet repeat </li></ul><ul><li>Huntington’s allele has 36 or more </li></ul><ul><ul><li>Produces too much glutamine amino acid, changing protein configuration </li></ul></ul>
  • 34. Genetic Anticipation <ul><li>Where symptoms appear earlier and with greater severity across generations </li></ul><ul><li>Repeats can expand over generations </li></ul><ul><li>One explanation for genetic anticipation </li></ul>
  • 35. Genomic Imprinting <ul><li>One gene from mother and one from father </li></ul><ul><li>Imprinted genes </li></ul><ul><ul><li>Parental contributor matters </li></ul></ul><ul><ul><li>Gene will or won’t be active </li></ul></ul><ul><ul><li>Maternally imprinted = from father </li></ul></ul><ul><ul><li>Paternally imprinted = from mother </li></ul></ul>
  • 36. Example: Igf2 <ul><li>Maternally imprinted (from father) </li></ul><ul><li>Influences embryo growth </li></ul><ul><ul><li>Insulin-like growth factor --> bigger embryo </li></ul></ul><ul><li>Mother </li></ul><ul><ul><li>“ Wants” large embryo, but not too large </li></ul></ul><ul><li>Father </li></ul><ul><ul><li>“ Wants” largest embryo possible </li></ul></ul><ul><ul><li>Cost to mother doesn’t affect father’s future reproductive output </li></ul></ul>
  • 37. Example: Chromosome 15 Deletions <ul><li>If deletion inherited from mother, causes Angleman syndrome </li></ul><ul><ul><li>Severe mental retardation, awkward gait, inappropriate laughter </li></ul></ul><ul><li>If deletion inherited from father, causes Prader-Willi syndrome </li></ul><ul><ul><li>Overeating, temper outbursts, depression, obesity, short height </li></ul></ul>
  • 38. Multiple-Gene Inheritance <ul><li>Polygenetic traits </li></ul><ul><li>Multiple genes interact to produce trait </li></ul><ul><li>Each individual gene inherited according to Mendelian laws </li></ul><ul><li>But interactive effect of genes (and environment) </li></ul>
  • 39. Quantitative Dimensions <ul><li>These are continuously distributed traits </li></ul><ul><li>Often approach a bell-curve </li></ul><ul><li>Applied to many psychological and biomedical traits </li></ul><ul><li>Correlational statistics (0.0 to 1.0) used to indicate resemblance between individuals </li></ul>

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