Lesson 4: Genetics and Behavior

Question 1

Maze-running in rats

Answer 1

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

Question 2

Basic Honeybee life cycle

Answer 2

• queen lays egg
• egg hatches into larva
• larva is fed by workers
• larva pupates and metamorphoses
• adult emerge

Question 3

Classical Genetics: Hygienic Behavior in
Honeybees: Hygienic Behavior

Answer 3

• 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

Question 4

Hygienic Behavior in Honeybees: experiments

Answer 4

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).

Question 5

Other test in hygienic behavior

Answer 5

• Backcross these heterozygous
  unhygienic offspring with
  hygienic homozygous recessive
  parents
• Result: four different types of
  behavior seen in offspring

Question 6

Hygienic Behavior in Honeybees – other observations

Answer 6

 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).

Question 7

honeybee speculation:

Answer 7

• 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?

Question 8

Imagine one gene, the hygiene gene, with two alleles, h and H. Now cross homozygous recessive (hh) with heterozygous dominant (Hh)

Answer 8

Result: Just two behaviors – either hygienic or unhygienic – but the real cross gave 4 behaviors so cannot explain
results with just one gene

Question 9

UR X ur

Answer 9

UuRr– heterozygous dominant for
both behaviors – no uncapping or
removal

Question 10

uR x ur

Answer 10

uuRr – homozygous recessive –
uncapping; heterozygous dominant –
no removal

Question 11

Ur x ur

Answer 11

Uurr – heterozygous dominant- no
uncapping; homozygous recessive -
removal

Question 12

ur X ur

Answer 12

uurr – homozygous recessive for
both behaviors – both uncapping
and removal are observed

Question 13

Inferring a Genetic Basis Based on Relatedness:
Animal personality

Answer 13

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

Question 14

regular water

Answer 14

low predation risk

Question 15

water from a tank with predatory fish

Answer 15

high predation risk

Question 16

results

Answer 16

• “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

Question 17

gene manipulations: knock outs

Answer 17

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

Question 18

gene manipulaions

Answer 18

• NMDA is a membrane-
  bound ion channel
• It is unusual in that it
  requires TWO signals to
  function

Question 19

Knockouts: The role of NMDA in the brain

Answer 19

• 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

Question 20

Knockouts: The role of NMDA in the brain — 2 events occurring simultaneously

Answer 20

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.

Question 21

Why is this interesting? (knockouts)

Answer 21

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

Question 22

Knock-outs and Knock-ins: Experiment: spatial
learning in mice

Answer 22

• 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)

Question 23

result: spacial learning in mice

Answer 23

• Result: Knock-out mice were
  slower than normal controls in
  learning position of the platform

Question 24

next step in mice spacial learning experiment

Answer 24

• 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.

Question 25

Genome-level analysis: Scouting behavior
in bees

Answer 25

• 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

Question 26

Genome-level analysis: Scouting behavior
in bees RESULTS

Answer 26

• 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

Question 27

The role of genes in determining behavior: ANTS

Answer 27

• 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

Question 28

Behavioral phenotype is the result of three factors

Answer 28

• Genotype at all loci that affect the behavior
• Environment animal experienced
• Gene-environment interactions (which often
  affect how gene is expressed)