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Proximate causes
• Interaction among gene/environment/ development persist and change over entire lifetime of animal
• We’re simplifying by focusing the “straight line” interactions for now
Behavioral Genetics
• Single gene effect - Drosophila sp.
• VT = VG + VE + VI
• VI = VG x VE
• Inbreeding - homogeneous strain - e.g. rearing condition (VG = 0, VT = VE)
• Strain difference (VE = 0, VT = VG )
• Hybridization - love birds, hygienic vs. unhygienic bees, cricket song
• Cross-fostering - e.g. cockatoo-reared galah
– galah begging call, alarm call,
– cockatoo contact call, slow wingbeat, food
Heritability• Degree of genetic determination
ratio of genetic variation in a behavior trait
• GD = VG /( VG + VE + VI)
• Cross inbred strains and measure behavioral variation
Mouse strainMean # wheel
revolution per 24 hrs VarinceA 1,107 112B 5,680 418
F1 (A x B) 5,235 325F2 (F1 x F1) 4,745 465
• VE = (112 + 418 + 325)/3 = 285
• VG = 465-285 = 180
• GD = VG / VT = 180/465 = 0.39
• Realized heritability, hr2 : a measure of
the response of a trait to selection
• Measure differences in behavioral traits between base stock and selected breeding parents (S), and between base stock and offspring (R)
• Selection differential, S • Response to selection, R
• hr2 =R/S
TREES 6(8): 254-262, 1991
• Genetic control of migratory behavior
• When to migrate?
Migratory pop. x Resident pop. => 40% of F1 migratory
The migratory restlessness may change by selective breeding
• How far?
---Long distance x Short distance => intermediate distance
• What direction?
---Resident x Exclusive migrant =>F1 migrant w/ parent direction
---SE migrant x SW migrant =>intermediate
---Species change direction during migration. Captive ones show same behavior
• Other migratory traits:
---morphological features
---seasonal change in feeding rate, food and habit preference, activity pattern
Group size preference• Proc. Nat. Acad. Sci. USA 97:
14825-14830
• Parent – offspring regression
• Group size of individual cliff swallow (Petrochelidon pyrrhonota) ~ parents
• Foster-raring individual ~ biological parents
• Naive animal - e.g. garter snakes and slug Mutation
• Twin studies
– identical (monozygotic) twins
– fraternal (dizygotic) twins
• Mosaic
• Quantitative Trait Locus Analysis (QLT)
Towards behavioral genomics
Science 291: 1232-1233, 2001
• Single genes do not determine most human behavior
• Nearly all behaviors that have been studied showed moderate to high heritability
• Environmental factors make people different from, rather than similar to, their relatives
• Information and techniques generated by the human genome sequence will help locate and identify genes involved in behavior
• Problems
– Detect genes of a linkage with large enough effects
– Most valid diagnostic schemes for genetic research
• A greatly improved map of human genome sequence helps improve allelic association studies to locate QTLs
• To ID the effects of QTLs
– Bottom-up: functional genomics and proteomics
– Top-down: behavioral genomics
– Genome sequences of other organisms
• Future perspectives
– Understanding the neurobiological basis of individual (behavioral) differences and a better grasp of the etiology of diseases
– Discovery of new and more specific drug treatments
• Limitation
– Gene-environment interplay
– Distribution of effective sizes of QTLs
Molecular techniques
• Transgenic
• Knockout
• Gene mapping and association
• Protein electrophoresis
• DNA fingerprinting
Per gene and song pattern• Observation –
– In both D. melanogaster and D. simulans wildtypes, difference in per alleles ~ differences in male songs (pleiotropy).
– Wildtype per alleles differ in different species
• Hypothesis – Intraspecific differences in song are caused by differences in the per alleles
Building a brainier mouse (Sci. Am. 42-48, 2000)
• Molecular basis of learning and memory
• Hebb’s learning rule – a memory is produced when 2 connected neurons are active simultaneously in a way that strengthens the synapse
• LTP – Long-term potentiation vs. LTD – Long-term depression of synaptic connection in hippocampus
• NMDA receptors require 2 signals: binding of neurotransmitter glutamate, membrane depolarization
• Dumb mouse – NMDA lack NR1 subunit in CA1 region, impairment in spatial memory and other task
• Young animals produce NR2B, old animals more NR2A in NMDA, NR2B stays longer than NR2A
• Smart mouse – extra copies of NR2B
• Test 1. Recognition of objects: smart mice explore only new objects, normal mice explore both old & new, remember objects 4~5 times longer
• Test 2. Remember fear longer
• Test 3. Fear extinction learning faster
• Test 4. Morris water maze, finding submerged platform in milky water – need analytical skill, learning and memory, ability to form strategies
• Learning and memory enhance problem-solving, but intelligence has many aspects