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Single gene effects on behavior. How do gene products affect behavior? What methods are used to study single-gene effects? Segregation analysis Gene mapping Differences in mRNA between individuals or cell types correlates with behavior Genetic engineering.

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Single gene effects on behavior


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single gene effects on behavior
Single gene effects on behavior
  • How do gene products affect behavior?
  • What methods are used to study single-gene effects?
    • Segregation analysis
    • Gene mapping
    • Differences in mRNA between individuals or cell types correlates with behavior
    • Genetic engineering
how do gene products affect behavior
How do gene products affect behavior?
  • If the central dogma is correct, i.e.:
  • DNA sequence -> mRNA sequence -> amino acid sequence = protein
  • How can a change in the DNA sequence influence behavior of the adult organism?
examples of how proteins can influence behavior
Examples of how proteins can influence behavior
  • Peptide hormones act as neurotransmitters
    • Dopamine, serotonin, oxytocin, vasopressin
  • Steroid hormone receptors allow responses to hormones
  • Signaling peptides can activate ion channels and alter neuronal sensitivity
  • Pigments can alter perception
  • Neuronal growth factors alter development
  • Transcription factors bind to DNA and can alter the amount and timing of transcription of other genes
methods for studying single gene effects on behavior
Methods for studying single gene effects on behavior
  • Find alternate alleles at a single locus
    • Segregation analysis
      • Natural variants
      • Create mutations (x-rays, EMS-ethylene methyl sulfide)
    • Gene mapping and association
  • Find differences in expression of candidate genes
    • Genetic mosaics
    • Expression studies
      • Northerns, microarrays, quantitative RT-PCR
    • Transgenics
      • substitutions, knockouts, viral-mediated gene transfer
simple segregation patterns
Simple segregation patterns
  • Two phenotypes
    • 3:1 ratio of offspring
      • AA x aa = (AA + 2Aa) + aa (A dominant, ex. tongue rolling)
    • 1:1 ratio of offspring
      • Aa x aa = Aa + aa (A dominant or codominant)
      • Aa x AY = AY + aY males (A dominant and on X, ex. red-green color blindness in males)
  • Three phenotypes
    • 1:2:1 ratio of offspring
      • AA x aa = AA + 2Aa + aa (A codominant)
dominance

Phenotype

No dominance = additive

aa Aa AA

Phenotype

aa Aa AA

Phenotype

Overdominance

aa Aa AA

Dominance
  • Exists whenever the phenotype of a heterozygote is not the average of the parental values
  • Attribute of a genotype, not an allele
  • May be scale dependent
  • Only relationships which can share genotypes can share dominance, e.g. full-sibs, twins

Complete dominance

single genes segregate foraging
Single genes segregate: foraging

Rover is dominant: all F1 and 3:1 F2

the foraging gene
The foraging gene
  • Rover allele is favored in crowded environments while sitter allele is favored at low densities
  • Expression of rover can be altered by restricting food
  • Located on chr 2, codes for an enzyme (cyclic GMP-dependent kinase) involved in cell signaling that influences how larvae respond to food quality
bee foraging and foraging
Bee foraging and foraging

Polyethism

Ben-Shahar et al. 2002 Science

drosophila courtship mutants
Drosophila courtship mutants

Note: pleiotropy, i.e. single gene effects two or more traits

gene mapping
Gene mapping
  • Genotype individuals from known pedigrees or from a segregating cross involving inbred strains (F2 or backcross)
  • Measure trait of interest
  • Find association between trait and marker presence
rflp association with huntington s chorea
RFLP association with Huntington’s chorea

Note that 33 of 34 affected individuals have the C allele; indicating

1 recombination event and tight linkage between C and HD genes

drosophila gynandromorphs genetic mosaics
Drosophila gynandromorphs (genetic mosaics)

Has been used to study where X-linked genes are expressed

during the first cell division

slide17

No vibrations

Vibrations

Dark = female

Light = male

transformation experiments show that per affects drosophila male courtship
Transformation experiments show that per affects Drosophila male courtship

D. melanogaster and D. simulans differ in the interpulse interval (IPI) in male courtship song.

The species differences are retained when pero mutant flies are transformed with conspecific

period genes.

Cross species transformations with per altered male behavior to approximate the other species.

Epistasis -

genetic background

affects behavior

fly memory and dunce rutabaga
Fly memory and dunce,rutabaga
  • dunce flies can’t form association between chemical odor and shock
  • Not a sensory problem
  • Have poor memory - association doesn’t last as long as normal
  • rutabaga also causes poor learning and memory
memory formation in flies
Memory formation in flies

dunce codes an enzyme

cAMP phosphodiesterase,

which breaks down cAMP

rutabaga has defective

adenyl-cyclase, which

forms cAMP from ATP

This pathway is also involved

in learning and memory in

the sea slug, Aplysia

Cyclic AMP Response Binding protein

slide21

Creating “knock-out”

or “knock-in” mice

vasopressin 1a receptor correlates with partner preferences in voles
Vasopressin 1a receptor correlates with partner preferences in voles

Prairie vole

Meadow vole

Partner, stranger

V1a receptor distribution

D2 receptor distribution

viral mediated transfer of v1ar alters partner preferences in voles

V1aR-vp

Control

Control - other

Eticlopride treatment

(blocks dopamine receptors)

Viral-mediated transfer of V1aR alters partner preferences in voles

Time experimental male spent huddling with partner (filled) or stranger (open) female

Lim et al. 2004 Nature

behavior genetics references
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