Transcript Behavioral Genetics

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
Mean # wheel
Mouse strain revolution per 24 hrs Varince
A
1,107
112
B
5,680
418
F1 (A x B)
5,235
325
F2 (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