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Announcements
1. Overview of ethics and recombinant DNA technology
2. Reminder: pre-lab questions for lab 13 due at start of
lab this week
Outline of Lecture 33
I. First approach to determine whether a behavior has
genetic components - examine differences in behavior
between closely related organisms
II. Second approach -selection of a preferred behavior from
a genetically heterogeneous population; can trait be
transferred by genetic crosses?
III. A single gene can control a single behavior, but most
behaviors are more complex
IV. Genetics of behavior in Drosophila
V. Genetics of human behavior
Genetics and Behavior
• One of the most interesting questions we can ask:
Why do we behave the way we do?
• Nature vs Nurture
– Genetics vs Learned
• Many behaviors are a combination of both
• What is genetically determined?
• It turns out that behavior is genetically dissectible,
just as the lac operon regulation or leucine
biochemical pathway is.
I. Alcohol Preference in Inbred Mice
Raised in same conditions. 3 weeks with choice of alcohol
concentrations.
== > C57BL & C3H/2 have preference for alcohol
Genetic basis unknown.
II. Selection of preferred behavior
Example 1: Maze Learning in Rats
Artificial Selection in Heterogeneous Population
(need genetic variation!)
82 rats. In successive tests, some rats come to make fewer
mistakes. Brighter rats (9 pairs) selected and bred. Same with slower.
Response to Selection
Bright rats are better than all dull rats.
But, this “cleverness” is task-specific.
The bright rats were inferior in water-escape tests, important to survival.
Example 2: Geotaxis (gravity) in Drosophila
Response to Selection (geotaxis)
Polygenic trait probably (fluctuation).
Tester cross (in text) allows the genes to be tested one
chromosome at a time.
III. Single gene can control single behavior
Nest-Cleaning in Bees
• Honeybee nests can get Bacillus infection (foulbrood
disease).
• Worker bees clean them with two “hygienic” behaviors:
– Uncap cell
– Remove bacteria
Most behaviors are controlled
by multiple genes
How do bacteria find their food?
E. coli Attracted by Chemical - How?
Run = CounterClockwise rotation (as shown)
Tumble = Clockwise rotation (other way)
E. coli movement: Run & Tumble
High chemical concentration causes longer runs
as E. coli get closer
Sensory Transduction during Bacterial Chemotaxis
4 Genes + Receptor
Repellent binding -> Che A phosphorlyation -> dephosphorylation ->
-> Che Y phosphorylation & binds to base
-> clockwise rotation & tumble
Attractant binding -> does opposite -> run
IV. Some Behavioral Mutants of Drosophila
Male behavior during courtship and mating
Genetic cross that helped recover X-linked induced mutations
V. Human Behavioral Mutations
• Huntington Disease (autosomal dominant)
• ** Monamine oxidase syndrome, (mental retardation &
aggression), enzymes degrade neurotransmitters.
– Typically hemizygous males (X-linked recessive)
• Lesch-Nyhan syndrome (X-linked recessive)
• Tay-Sachs Disease (autosomal recessive)
• Phenylketonuria (autosomal recessive)
• Down Syndrome (tri-21 or translocation)
• ** Schizophrenia
– 1/100
– Delusional behavior (- not depression -)
– High concordance in monozygotic twins
– Polygenic (3-6 genes)
– One on human chromosome 22
– "A Beautiful Mind", 2002 Best Picture Academy Award
• ** Alzheimer's Disease
Alzheimer's Disease
• Brain: hippocampal neurons degenerate, short-term
memory decreases as does thinking, ability to care
for oneself.
• Brain deposits called neuritic plaques and cells have
neurofibrillary tangles (best diagnosis on autopsy).
• Over 25% of those over 85 yrs have it.
• Most get the late-onset sporadic form, but some have
early-onset inherited form.
Alzheimer's Disease - cont.
Genes
• Chrom. 21, APP = amyloid precursor protein gene (-> a
protease inhibitor in the membrane)
– Incorrect processing -> ~40aa beta-amyloid.
– May poison cholinergic neurons
– The inherited mutation in some families, but also in many
sporatic cases of Alzheimer's
• Chrom. 19, apoE (apolipoprotein E) gene
– Early onset, inherited; also sporatic
– The mutation apoE4 product binds tightly to beta-amyloid
• Chrom. 14
– Early onset, inherited
• Treatment (none)
– April 2002, mice, vaccination w/ beta-amyloid helps
– Inhibitors of neurotransmitter acetylcholinesterase delay
symptoms but don't cure.