Lesson 4: Genetics and Behavior Flashcards
Maze-running in rats
Can study the effect of
environment on genetically
-influenced behavior by
raising same strain in
different environments
- Environments differed in
the amount of novelty
the animals experienced
while growing up - Rats were then tested as
adults in the maze
Basic Honeybee life cycle
- queen lays egg
- egg hatches into larva
- larva is fed by workers
- larva pupates and metamorphoses
- adult emerge
Classical Genetics: Hygienic Behavior in
Honeybees: Hygienic Behavior
- Involves identifying and
removing larvae that have
died from American
Foulbrood bacterial infection - Some hives show this
behavior & survive the
disease; others don’t and
are wiped out
Hygienic Behavior in Honeybees: experiments
Identified hives that “bred true.” That is,
all offspring were the same.
- Crossed hygienic x unhygienic hive
- Result: all offspring were unhygienic
- Conclusion: unhygienic behavior is
dominant
- & furthermore, the hygienic hive must
be homozygous recessive (and the
unhygienic hive in this case is
homozygous dominant as well).
Other test in hygienic behavior
- Backcross these heterozygous
unhygienic offspring with
hygienic homozygous recessive
parents - Result: four different types of
behavior seen in offspring
Hygienic Behavior in Honeybees – other observations
Behavior split into two
different behaviors: uncapping
& removal
Some bees did both
Some did neither
Some only uncapped
Others removed (if someone
else had already uncapped).
honeybee speculation:
- If have one gene (say H for hygiene), then heterozygous dominant parent would be Hh and homozygous
recessive would be hh - So what happens if cross Hh x hh?
Imagine one gene, the hygiene gene, with two alleles, h and H. Now cross homozygous recessive (hh) with heterozygous dominant (Hh)
Result: Just two behaviors – either hygienic or unhygienic – but the real cross gave 4 behaviors so cannot explain
results with just one gene
UR X ur
UuRr– heterozygous dominant for
both behaviors – no uncapping or
removal
uR x ur
uuRr – homozygous recessive –
uncapping; heterozygous dominant –
no removal
Ur x ur
Uurr – heterozygous dominant- no
uncapping; homozygous recessive -
removal
ur X ur
uurr – homozygous recessive for
both behaviors – both uncapping
and removal are observed
Inferring a Genetic Basis Based on Relatedness:
Animal personality
Obtained 10 sets of 4 sibling larval
salamanders (each set came from the
same egg mass)
- Raised each larva alone in an
aquarium with a refuge (hiding place)
so that they did not interact with other
salamanders
regular water
low predation risk
water from a tank with predatory fish
high predation risk
results
- “low-risk” larvae spent less
time in refuge than the
“high-risk” larvae
There was a linear
correlation between time
spent out of refuge when it
was ‘safe’ and when it was
‘risky’.
- That is, if an individual was
bold when it was ‘safe’ it
would still be bold when it
was ‘risky’ - Siblings were similar to each
other – implying that the
phenotype of being bold or
shy has an underlying genetic
basis
gene manipulations: knock outs
We can look at the role of genetics using gene
manipulations. For example, we can ‘knock-out’ a gene by making it non-functional or deleting it from an individual’s chromosomes. We can then study the effect of the knock-out on behavior
gene manipulaions
- NMDA is a membrane-
bound ion channel - It is unusual in that it
requires TWO signals to
function
Knockouts: The role of NMDA in the brain
- First, the nerve cell must
be electrically stimulated
(note we draw +++ inside
the cell to show that it is
electrically stimulated.
Nerve cells are usually
negative inside. - Second, glutamate must
bind to the outside of the
NMDA molecule
Knockouts: The role of NMDA in the brain — 2 events occurring simultaneously
When the two events occur
simultaneously, then a
magnesium ion shifts position
and the NMDA molecule
opens up and allows calcium
ions into the cell.
Why is this interesting? (knockouts)
NMDA receptors are
found in neurons in the
hippocampus – a part of
the brain important in
memory and long-term
learning
- Because NMDA involves
TWO signals, it could be
a mechanism for
associating TWO
events in time – a basic
feature of learning
Knock-outs and Knock-ins: Experiment: spatial
learning in mice
- The first experiment involved making
“knock-out” transgenic mice – these
lacked the gene for NMDA - They were then tested for the ability to
remember the spatial arrangement of a
swimming chamber (the hidden
platform test)
result: spacial learning in mice
- Result: Knock-out mice were
slower than normal controls in
learning position of the platform
next step in mice spacial learning experiment
- Next made mice that overexpressed NMDA
– called “knock-in” mice - These learned more quickly than normal
controls. - So the conclusion is that NMDA is involved
in learning and memory - Why not overexpress it all the time? Turns
out overexpression associated with
increased pain perception and
neurodegenerative problems.
Genome-level analysis: Scouting behavior
in bees
- When bees leave the hive to go find
food, only about 25% of individuals act
as food scouts and search out NEW
food sources; the rest go to areas the
scouts find
—Question: what makes a scout be a
scout?
Liang et al. 2012 used knowledge of
the honeybee genome to look at food
scouting behavior
- In order to identify food scouts, they
provided a series of different feeders
to bees in a huge flight cage. Bees that
were able to find multiple food sources
were more “exploratory” and were
called ”scouts” - Conducted whole-genome RNA
analysis (transcriptomic analysis) on
scouts and non-scouts
Genome-level analysis: Scouting behavior
in bees RESULTS
- 16% of mRNA transcripts exhibited
significant differences between
scouts and non-scouts - Many of these genes were related to
neurotransmitters associated with
novelty-seeking behavior in
vertebrates - The point: behavior likely influenced
by which genes are active
The role of genes in determining behavior: ANTS
- All of these ants could be genetically
identical. - The different sizes and shapes
reflect differential gene expression
triggered by exposure to different
chemicals as larvae. - Worker ants feed different
compounds to different larvae. - So this is one basis for gene-
environment interactions
Behavioral phenotype is the result of three factors
- Genotype at all loci that affect the behavior
- Environment animal experienced
- Gene-environment interactions (which often
affect how gene is expressed)
