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Reverse Genetics GenotypeDriven
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Knock-out (null mutant), Knock-in: gene expression is disabled (knock-out) or ... Epigenesis. Final Admonitions. Don't believe it unless it is replicable ... – PowerPoint PPT presentation
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Title: Reverse Genetics GenotypeDriven
1
Reverse Genetics(Genotype-Driven)
- Bottom ? up approach (i.e., from genotype to
phenotype) to determine gene effects - Transgenic - inserting foreign DNA into an
animal - Huntington
- Alzheimers
- ALS
- Knock-out (null mutant), Knock-in gene
expression is disabled (knock-out) or enhanced
(knock-in) - Original model was Lesch-Nyhan (hprt)
- There are knock-out models of most genes we have
discussed - - Over expression of DRD2 ? reduced alcohol
consumption - 5-HTT knockout ? increased alcohol sensitivity
and reduced alcohol consumption
2
Summary
- Classical methods for establishing heritability
- Inbred strains
- Selective breeding
- Genetic Correlation
- Correlated response to selection
- Inbred strain correlations
- Component Phenotypes
- Preference and Sensitivity are inversely
associated - Metabolism assoc with preference but not
sensitivity - Withdrawal susceptibility largely a genetically
independent phenotype
3
Summary
- Forward Genetic Approaches (phenotype-driven)
- QTL Analysis ? Candidate genes candidate
regions - Mutation Screens
- Microarray analyses
- Reverse Genetic Approaches (genotype-driven)
- Transgenics
- Knockouts/Knockins
4
Behavioral GeneticsTopic 13
- ALDH
5
Flushing Response
- Dysphoric effects that occur w/i 15 minutes of
drinking - Heart palpitation
- Facial reddening
- Nausea, dizziness
- There are large ethnic group differences in rate
of flushing metabolic not cultural
6
Inherited ALDH2 Deficiency
NAD
NAD
Alcohol
Acetaldehyde
Acetate
ALDH2 Mutation
ADH
ALDH
7
ALDH2 Deficiency
- Mutation (ALDH22 v wild-type ALDH21) is a
single nucleotide change in exon 12 that results
in a glu/lys exchange in position 487 - Deficient form of the enzyme carried by approx
50 of Northern East Asians but only 2 of
alcoholics from those regions
8
ALDH2 Deficiency Among Japanese Alcoholics
(Higuchi et al. 1994)
Heterozygote Frequency
9
Psychology 5-137
- Topic 14
- Conclusion
10
Methodologies
- Mendelian (single-gene) inheritance
- PKU, Huntingtons, CAH
- Chromosomal anomalies/Structural Variation
- Down Syndrome, Williams Syndrome, VCFS
- Twin/Adoption Studies
- Complementary methodologies
- Biometric Analysis
- Variance component estimation
- Gene Identification in Humans
- Linkage, Association, Linkage Disequilibrium
- Animal Methods
- Selection, Inbred Strains,
- Forward Genetics (QTL, mutagenesis, microarray),
Reverse Genetic (transgenics, knock-outs)
11
Nature of Genetic Influence
- Heritability
- Virtually all behavioral traits are in part
heritable - Common heritable factors may account for
correlations among disorders - Heritability estimates are approximations
- Heritability is neither an index of immutability
nor an explanation of behavior
12
Principled Critiques of BG
- For psychologists, as well as for medical
researchers, the purpose of identifying
undesirable predispositions of individuals should
be to devise more effective health-promoting
interventions, not to discourage such attempts on
the supposition that these predispositions are
genetically based and therefore intractable.
- D. Baumrind (1993)
13
Burmeister, M. et al. (2008). Psychiatric
genetics Progress amid controversy. Nature
Reviews Genetics. 9 527-540.
14
Nature of Genetic Influence
- Genes and the Human Genome Project
- 20,000 to 25,000 genes and 11,000,000 SNPs, and
large amount of structural variation (e.g., CNVs)
- Gene identification has been difficult
- Mendelian vs. oligogenic vs. polygenic
- Positional cloning strategy has produced few
successes - But there are some leads
- Prospects for the Future
- GWAS under the CDCV model
- Will require very large samples
- Pooling of resources across labs
- CNVs for rare mutations?
- Animal experimental approaches
15
What is the likely benefit of finding genes for
human behavior?
- Better understanding of the nature and origins of
behavior - Pharmacological interventions based on genotype
(the 5-HTT example) - Targeted early prevention (e.g., treating
unaffected siblings of schizophrenics?) - What is the significance of small gene effects?
- Familial hypercholesterolimia affects 0.2 and
acounts for a small portion of heritability led
to development of statins
16
Merikangas, K.R. Risch, N. (2003). Genomic
priorities and public health. Science, 302
599-601.
The potent effect of pervasive societal changes
on this behavior will far outweigh any possible
benefits of identification of risk genes ... (p.
601)
17
Nature of Environmental Influence
- Familial resemblance is potentially a function of
both shared genes and shared environment - Have we overestimated the impact of parents?
- Shared vs. non-shared environmental effects
- Changing balance across development for some
traits - SZ, BP, Depression, ADHD
- Gene-environment interplay
- GxE and the diathesis-stress model
- PKU
- MAO-A and aggression
- 5HTTLPR and depression
- G-E correlation
- Ge et al. adoption study
- Epigenesis
18
Final Admonitions
- Dont believe it unless it is replicable
- Single studies are not definitive, require a
coherent pattern of results - Study for the final attend review session on
Tuesday 16 December 10-12, N227 Elliott - Arrive for the final on time (130-330PM,
Wednesday 17 December in N119 Elliott Hall), and
