• How do gene products affect behavior?
• What methods are used to study singlegene effects?
– Segregation analysis
– Gene mapping
– Differences in mRNA between individuals or cell types correlates with behavior
– Genetic engineering

• 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?

• 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

• 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

• 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)

• 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
No dominance
= additive aa Aa AA
Complete dominance aa Aa AA
Overdominance aa Aa AA

Rover is dominant: all F1 and 3:1 F2

• 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

Polyethism
Ben-Shahar et al. 2002 Science

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

• 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

Note that 33 of 34 affected individuals have the C allele; indicating
1 recombination event and tight linkage between C and HD genes

Chromosome locations for human disorders

Drosophila gynandromorphs (genetic mosaics)
Has been used to study where X-linked genes are expressed during the first cell division

Dark = female
Light = male
No vibrations Vibrations

D. melanogaster and D. simulans differ in the interpulse interval (IPI) in male courtship song.
The species differences are retained when per o 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

• 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

rutabaga has defective adenyl-cyclase, which forms cAMP from ATP dunce codes an enzyme cAMP phosphodiesterase, which breaks down cAMP
This pathway is also involved in learning and memory in the sea slug, Aplysia
Cyclic AMP Response Binding protein

Prairie vole
Meadow vole
Partner, stranger V1a receptor distribution D2 receptor distribution

V1aR-vp Control
Control - other
Eticlopride treatment
(blocks dopamine receptors)
Time experimental male spent huddling with partner (filled) or stranger (open) female
Lim et al. 2004 Nature

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