Psychology 372

1. Psychology 372 Behavioural Genetics

2. Behavioural Genetics • Studies the role of genetics and environment in animal behaviour • Intersects with psychology in general (especially developmental, abnormal, clinical), human behavioural ecology, evolutionary psychology, genetics, population genetics • Actually, an older field than psychology

3. Sir Francis Galton • Hereditary Genius (1869) • “…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.” • Beginning of behavioural genetics • Family and twin study designs • Correlations and regressions Galton at age 50 <www.galton.org/>

4. Early Behavioural Genetics • Traditionally, studied inheritance of behavioural traits • Demonstrate genetic influence on behaviour exist • Conflict with Behaviorism

5. Behaviorism • John B. Watson • “Hard-line” Behaviorism • “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.” • Predominant in psychology and social sciences until 1960s • Environmental control over behaviour with no or minimal genetic influence

6. Nature and Nurture • Back to 17th century philosophy • Empiricism • Tabula rasa • Nativism

7. Determinism • Genetic determinism • Genetic predispositions

8. Contributing Factors • Interaction • Nature • The genes • Nurture • Shared environment • Unique/non-shared environment

9. Heritability Estimates Correlation of Sibling Traits in Shared Family Environment • Trait 1: low heritability, high shared environment • Trait 2: high heritability • Trait 3: low heritability, low shared environment, high unique environment 1.0 0.8 0.6 0.4 0.2 0 Correlation Trait 1 Trait 2 Trait 3 Monozygous twins Biological siblings Adoptive siblings

10. More Recent Trends • Shift from study of inheritance • Use of quantitative methods • Estimates degree to which differences in individuals are due to genetic and environmental differences; doesn’t specify gene or environmental factors • Molecular genetics • Identification of specific genes for behaviours • Study of quantitative trait loci (QTLs)

11. Genetic Components • We’ll get to the behaviours • Need a basic familiarity with genetic terminology and elements

12. Terms • Gene • Smallest discrete inherited unit • Allele • Different forms of specific gene • Two alleles of each gene • Homozygous or heterozygous • Alleles can be dominant or recessive • Genotype and phenotype

13. Punnett Squares • Standard is to use capitals for dominant, lower-case for recessive • Will produce all the possible genotypic outcomes • Assumes genes are independent of each other • Punnett Square Calculator

14. Chromosomes • 23 pairs of chromosomes in humans • 22 autosomal, 1 sex • Loci (locus, singular) of gene(s) <adapted from: www.accessexcellence.org/ RC/VL/GG/human.php> <encarta.msn.com/media_461543483/Human_Male_Karyotype.html>

15. Meiosis and Mitosis • Mitosis • Non-gamete cell division • Mitosis animation • Meiosis • Production of gametes • Meiosis animation

16. Gregor Mendel • Augustinian priest • Well trained in mathematics, physics, biology • From 1856-1863 cultivated and tested 29,000 pea plants • Sought to understand variation • Work published in 1866, but largely ignored until rediscovered in 1900 • Two laws of heredity <en.wikipedia.org/wiki/Image:Mendel.png>

17. Mendel’s First Law of Heredity • Law of Segregation • Genes “segregate” during gamete formation • Offspring receive one gene from each parent • Dominant and recessive forms

18. Mendel’s Second Law of Heredity • Law of Independent Assortment • Inheritance of one gene is not affected by the inheritance of another gene • Does get violated in various situations • Linkage based on proximity of loci on chromosome • Recombination (chromosomal crossovers) • Recombination between linked genes animation

19. Hardy-Weinberg Equilibrium • Frequencies of alleles and genotypes don’t change across generations unless forces (e.g., natural selection, migration, etc.) alter them • For a population, can calculate allele and genotype frequencies, assuming random mating

20. Frequencies • Consider a single locus with two alleles • Dominant A and recessive a • Frequency(A) = p • Frequency(a) = q • Expected genotype frequencies are the product of the mother’s (p + q) and father’s alleles (p + q) • Thus, (p + q)2 = p2 + 2pq + q2

21. Punnett Square and Hardy-Weinberg Eggs A a (p + q)2 = 1 p2 + 2pq + q2 = 1 AA (p2) 0.6x0.6 = 0.36 Aa (pq) 0.6x0.4 = 0.24 A a p = 0.6 Sperm Aa (pq) 0.6x0.4 = 0.24 aa (q2) 0.4x0.4 = 0.16 q = 0.4 p = 0.6 q = 0.4

22. Example • 1 in 1700 US Caucasian newborns have cystic fibrosis • C for normal is dominant over c for cystic fibrosis • What percentage of the population have cystic fibrosis? • Genotype cc is q2, so: • q2 = 1/1700 = 0.00059 = 0.059%

23. Allele Frequencies • Then the frequency of the c allele is • c = q = square root of 0.00059 = 0.024, or 2.4% • Now, to find the frequency of C, • C = p = (1 - q) = 1 - 0.024 = 0.976, or 97.6%

24. Genotype Frequencies • Frequency of homozygous dominants (CC) • p2 = 0.9762 = 0.953, or 95.3% • Frequency of heterozygous condition (Cc) • 2pq = 2(0.976 x 0.024) = 0.0468, or 4.68% • Thus, out of 1700 people, 1620 are homozygous dominant (CC), 79 are heterozygous carriers (Cc), and 1 is homozygous recessive (cc)

25. Autosomal Chromosomes • In humans, 22 autosomal chromosomes • All chromosomes have a short (p) and long (q) arm • When stained, distinct “bands” appear on the chromosome • Locations of genes identified by the chromosome number, the arm, the region, and then the band • E.g., 5p14 is chromosome 5, arm p, region 1, band 4 Chromosome 5 p arm q arm

26. Sex Chromosomes • Two chromosomes that differ for males and females • XX and XY • Sex-determining region Y (SRY) • Gene located on short arm of Y chromosome • Master switch triggering events converting the embryo into a male; without the gene, embryo is female • Evidence: aneuploid humans with karyotypes XXY, XXXY, even XXXXY are all functionally male • SRY transgenic XX karyotype mice <http://users.rcn.com/jkimball.ma.ultranet /BiologyPages/S/SexChromosomes.html>

27. Sex Linked Genes • X chromosome carries hundreds of genes • Few have anything to do directly with sex • Special rules of inheritance because • Males have only single X chromosome • Almost all genes on X have no counterpart on Y, thus • Any gene on X, even if recessive in females, will be expressed in males • Genes inherited in this fashion are called sex-linked, or X-linked

28. Hemophilia Example • Blood clotting disorder • Mutant gene encoding clotting factor VIII on X chromosome • With only one X chromosome, males who inherit defective gene from their mother are unable to produce factor VIII and are hemophiliacs • For heterozygous female carriers, the normal copy of the gene provides the needed factor VIII

29. More Exceptions to Mendel’s Laws • Mutations • Chromosomal errors • Repeat sequences • Genomic imprinting

30. Mutations • Many genetic diseases involve spontaneous mutations • Majority of mutations do nothing • Of those that do something, practically all are “bad” (i.e., create a disfunction from “normal”) • Only very, very occasionally does a mutation confer a benefit to the individual • We’ll come back to mutations in chapter 4

31. Chromosomal Errors • Nondisjunction • Failure to apportion chromosomes equally during meiosis • Generally leads to spontaneous abortion in first few weeks post conception • Down syndrome • Three copies (trisomy) of chromosome 21 (one of the smallest chromosomes) • Monosomy (one copy) of a chromosome seems to always be fatal (would be missing essential genes)

32. Repeat Sequences of DNA • 1 to 4 nucleotide bases repeat up to a few dozen times • Don’t really know why these repeats occur • Common and normal; perhaps up to 50,000 places in human genome • Problem when number of repeats at a particular loci increase beyond normal range

33. Example: Huntington’s Disease • Repeat of three bases (triplet repeat) on chromosome 4 • Normal (non-Huntington’s) people have 11-34 copies of triplet repeat • Huntington’s allele has 36 or more • Produces too much glutamine amino acid, changing protein configuration

34. Genetic Anticipation • Where symptoms appear earlier and with greater severity across generations • Repeats can expand over generations • One explanation for genetic anticipation

35. Genomic Imprinting • One gene from mother and one from father • Imprinted genes • Parental contributor matters • Gene will or won’t be active • Maternally imprinted = from father • Paternally imprinted = from mother

36. Example: Igf2 • Maternally imprinted (from father) • Influences embryo growth • Insulin-like growth factor --> bigger embryo • Mother • “Wants” large embryo, but not too large • Father • “Wants” largest embryo possible • Cost to mother doesn’t affect father’s future reproductive output

37. Example: Chromosome 15 Deletions • If deletion inherited from mother, causes Angleman syndrome • Severe mental retardation, awkward gait, inappropriate laughter • If deletion inherited from father, causes Prader-Willi syndrome • Overeating, temper outbursts, depression, obesity, short height

38. Multiple-Gene Inheritance • Polygenetic traits • Multiple genes interact to produce trait • Each individual gene inherited according to Mendelian laws • But interactive effect of genes (and environment)

39. Quantitative Dimensions • These are continuously distributed traits • Often approach a bell-curve • Applied to many psychological and biomedical traits • Correlational statistics (0.0 to 1.0) used to indicate resemblance between individuals