Transcript Cells

Cells and Genes
Biology/Psychology 2606
Introduction
• We touched a teeny bit on neurons and glial
cells last time
• Let’s get into it in detail
• Neurons are the basic information processing
unit of the nervous system
• It may be the case that single neurons can
control behaviour and store information
• Other times (perhaps more commonly)
networks of neurons do this
Amazing neuron facts
• Impress your friends and be the life of the
party with these ice breakers
• 1) You are born with almost all of your
neurons
• 2) Neurons change with experience
• 3) If they do not make connections, they die!
• 4) We CAN grow new ones in the CNS
• 5) Genetic blueprint can be ‘reopened’
Some Cell anatomy and physiology
• Axons and dendrites increase the cell’s
surface area greatly
• Dendrites are even bigger due to dendritic
spines
• Only one axon
• Starts at the axon hillock
• Might be many branches of the axon, these
are called teleodendria
Cells have lots of parts
• Terminal button
• Connects with next dendrite
– Though there is a gap, the synapse
• Information basically travels down from the
dendrite, through the axon, to the next
dendrite and so on
Different types of neurons
• Bipolar neuron, short
dendrite, short axon
• Sensory neuron has
more connections
• Interneurons
– Association (stellate cell)
– Pyramidal
– Purkinje
• Motor neuron
– Synapses to a muscle
A little bit about synapses
• Recent discovery
– (though Sherrington figured it out earlier on)
• Chemical messages (neurotransmitters)
• Feedback
• Excitation and inhibition
– With many connections this is a relatively complex
calculation, and there is a temporal window and a
spatial one too!!
Glial Cells
Glial cells keep your brain running on
time…
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Well indeed, they serve a repair function
Say you get a deep cut, you may get paralysis
Old axon dies
Microglia and Schwann cells go into the
pathway and sort of clear the way for a new
axon
• Neuron sprouts until it finds the path
Too bad this doesn’t happen in the CNS
• Glial cells sort of seal off any injury
• Actually secrete a chemical (NOGO) that stops
growth!
• There has been some success with blocking
NOGO, using tubes, using stem cells etc
Elements
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H
C
O
N
Ca
P
K
S
Na
Cl
Cell anatomy
Genes, cells, Proteins and behaviour
• ‘Trying to determine how much of a behaviour
is due to genetics and how much is due to the
environment is like trying to determine how
much the area of a field is caused by its length
and how much by its width’
Donald Hebb
• Nature v. Nurture is a stupid argument
Key Terms
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Gene
Genotype
Phenotype
Chromosome
Locus
Allele
Diploid
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Haploid
Gamete
Zygote
Recessive
Dominant
Homozygous
Heterozygous
• Note that it is not the
case that the
chromosomes just pair
off, there is also
recombination
• So, each sex cell is a
little bit different
• This Recombination is the source of much
genetic variation, and it occurs in all but the
simplest organisms
• Mutation is the ONLY source of new genetic
material
– Most mutations are bad, usually lethal
– Some are neutral
– Some (very few) confer an advantage
A little background
• You get half of your genes from your mother
and half from your father
• Single genes can affect a characteristic
• Many genes can affect a characteristic
• It is always an interaction
An Example
• Human Ocular cutaneous albinism
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I wonder where that example came from…..
• Single gene involved in the the production of
melanin
• A – normal
• a - bad
• Dominance / Recessive relationship
• AA, aA, Aa all lead to normal, aa leads to me
• Rick and Leslie
• Aa and Aa
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Or some variation
aA and Aa
Aa and aA
aA and aA
• Phenotypically normal
• 1 in 4 chance of having
a kid with aa
• They did, on June 23,
1965
• My genotype MUST be
aa because there is no
dominance
They got the looks, but I got the brains……..
• Danny and Stephanie
may be carriers, or they
may not be, they are
phenotypically normal
• Their kids could carry
the allele, assuming
they do
• My kids MUST carry the
allele, as they had an a
from me, and, an A
from Isabelle
• We know they got an A
from Isabelle by looking
at their phenotype
Behavioural Effects
• I don’t spend much time in the sun
• I have very poor vision (20/200, melanin
guides the growth of the visual system)
• No binocular vision
• Can’t drive a car
• Not very good at baseball
• Huge IQ…….
Another cool example
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Mutant hamsters
Martin Ralph
Tau gene
TT normal 24 hr cycle
tt 20 hr cycle
Tt or tT gives 22 hr cycle
Teenage Mutant Ninja Hamsters
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Single Gene effect
Affects brain development
SCN specifically
May be cognitive effects
Learning Mutants in Drosophila
• The white rat of
genetics
• Dunce
• Amnesia
• Stuck
• Coitus interruptus
• Bang sensitive
• Per
– This one is cool…
So, What Does it All Mean?
• What does ‘a gene for behaviour’ mean?
– Behavioural difference caused by genetic difference
– Does not mean that a complex behavioural sequence is
caused by a single gene
• Many other genes contribute to behaviour
• Some difference must be caused by genetic differences
• Just because something has a genetic basis does not
make in unchangeable!!!!
• Remember, Genotype is NOT Phenotype