Behavioral genetics

what is behavioral genetics?
are of psychology that involves use of genetic methodologies to study nature and origins of individual differences in human and animal behavior (evolutionary psychology=studies how evolution shaped common psych. processes)

Plato on genetics
“The best men must cohabit with the best women” -The Republic

Aristotle on genetics
“and from deformed parents deformed offspring come to be” -History of animals

Shakespeare on genetics
“a devil, a born devil, on whose nature nurture can never stick” -The tempest

Linnaeus contributions to modern genetics
species–natural theology (cataloguing/classifying organisms)

Erasmus Darwin contributions to modern genetics
grandfather of Charles–poetry on evolution

Jean Lamark contributions to modern genetics
Inheritance/adaptation–giraffes evolved to have long necks (18th century)

Lyell contributions to modern genetics
time and gradualism–rock cycle-imperceptibly slow change (19th century)

Malthus contributions to modern genetics
competition and non-random loss–beginning of eugenics (18th and 19th century)

H.M.S beagle 1831
observations of tortoises and finch in galapagos islands

Alfred Wallace
1858 wrote to Darwin with theory–Origin of Species 1859

Sir Francis Galton
founder of behavioral genetics, differential psychology and biometry–first published BG study 1869 (rate of eminence)

Sir Francis Galton nature nurture debate
Nature prevails over nurture when environments are controlled

Henry Herbert Goddard
sort of founder of and believer in eugenics

Well known names who supported eugenics
Teddy Roosevelt, Margaret Sanger

3 ways eugenics influenced public policy in the early 20th century
1. immigration restriction act 1924
2. sterilization laws
3. upheld in court (carrie and emma buck-“three generations of imbeciles is enough”)

John B Watson eugenics view
nurture is everything (1924)

Richard Dawkins eugenics view
it is unethical to bring a down’s baby into the world

Gregor Mendel 1st law
Law of segregation–sperm and egg each contribute an allele

Mendel 2nd law
law of independent assortment–different traits have equal opportunity of occurring together

Huntington disease is ___________
autosomal dominant

PKU is a _____________ disease
autosomal recessive

Lesch-Nyhan is a ____________ disease
X-linked recessive

types of inherited influence
monogenic (single-gene, mendelian), multi-genic (galtonian, multifactorial, polygenic, oligogenic–disorders with complex genetics), mitochondrial

short arm of a chromosome
p

long arm of a chromosom
q

alternative forms of a locus are termed
alleles

human genome consists of ____ pairs of _______ chromosomes
23, homologous (first 22 autosomes last pair sex)

diploid chromosome
one inherited from mom and one from dad

haploid chromosomes
only one of each pair transmitted to offspring

mitosis definition
in dividing cells the process by which genetic material is duplicated to produce two identical daughter cells (diploid-diploid)

chromosomes usually visualized during which phase mitosis?
metaphase

mosaicism definition + how it happens
def: existence of multiple genetically distinct cell populations. Happens from nondisjunction of sister chromatids (mosaic down syndrome–extra chromosome on chrom 47/46)

Meiosis definition
production of gametes–genetic material is reduced by half (diploid-haploid)

Aneuploidy def
error in meiosis–nondisjunction of homologous chromosomes (downs-chrom 21 extra)

Recombination def
exchange of genetic material

Anticipation def (genetics)
an inherited disorder whose age of onset gets earlier, or prevalence or severity increases across successive generations (HD)

HD molecular bio cause
trinucleotide repeat expansion

Variable expressivity
same genotype different phenotype–choreic/rigid forms HD

genetic heterogeneity
different genotypes same phenotype

gene function
primary function far removed from behavior

pleiotropy
genes have multiple phenotypic effects

PKU def
deficient enzyme that converts phenylalanine to tyrosine

Non-coding DNA types
pseudogenes (evolutionary relics), repetitive DNA (interspersed, minisatellite repeats 10-30bps, microsatellite repeats <10 bps), regulatory regions, intragenic

polymorphism
allele w/ fequency less than or equal to 1%

mutation (rare and low freq.)
allele w/ frequency greater than 1%

genetic variants
genetic differences among individuals

CNVs
copy number variants–DNA where individuals carry other than the normal 2 copies

GWAS arrays
survey 500,000 SNPs in a large array to effectively skim the genome and identify disease causing loci BUT can’t look at SV’s

Whole genome sequencing
sequences all 3 billion bases and can see SV’s as well as SNP’s BUT expensive

Shotgun sequence reads
<25-100 bps must be aligned to be informative

transitions account for _______ variants
most

transversions account for ________ variants
minority of

Haplotype
set of DNA variations that tend to be inherited together

narrow sense heritability
proportion of phenotypic variance attributable to additive effects

broad sense heritability
proportion of phenotypic variance attributable to all genetic effects

passive GxE correlation
parents who transmit genes that promote development of a specific trait are likely to also create a rearing environment that fosters the development of that trait (Smoking)

reactive gxe correlation
our experiences are in part a function of the reactions our behaviors elicit from others, and to the extent our behavior is genetically influenced, this induces gxe correlation (cholic baby)

active gxe correlation
abilities/skills genetically influenced–individuals will seek out different environments because of their genes

MZ twins are not like the rest of population (4 ways)
infant mortality, cerebral palsy/neurodevelopmental delays, left-handedness, learning disorders

MZ twins are like the rest of the population (3 ways)
risk for psychopathology, cognitive ability, personality

MZ twinning 3-5 days post fertilization
dichorionic and diamnionic

MZ twinning 5-10 days post fertilization
single chorion separate amnions

MZ twinning 10-13 days post fertilization
monochorionic and monoamnionic

% dichorionic MZ twins
1/3

limitations of adoption research (3)
feasibility, selective placement, representativeness

uses of adoption studies
adopted siblings, quasi intervention, parent-offspring

positional cloning where do we look?
non-targeted: entire genome
Targeted: chromosomal anomaly, biologically based hypothesis, animal models, positive linkage results, expression studies, results from non-targeted

linkage analysis advantages
feasible to implement genome-wide/well developed and understood technology

linkage analysis disadvantages
requires family study design, good for variants w/ large effect but low power for common, limited resolution, does not find causal variant

allelic association/candidate gene studies advantages
easy to set up, theoretically high power, theoretically high probability of identifying causal variant

candidate studies disadvantage
need to know functional polymorphism, concern about false positives due to mismatching cases/controls

population stratification
causes false positive in candidate gene studies by creating artificial association that is actually due to different allele frequencies in a population

winners curse
another reason candidate gene studies fail; initial significant findings are overestimated

how can linkage disequilibrium cause false positives in candidate gene studies ?
they are non-random and population-level associations between non-functional genetic markers and phenotypes

common disease common variant model
due to combined effect of multiple genetic variants each of which is common, ancient, and has a small individual effect

common disease rare variant model
due to separate effect of multiple genetic variants each of which is rare, recent, and has a moderate to large effect

human populations differ. This genetic variation is:
predominantly within rather than between groups

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