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…

• 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• 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

• Gene• Genotype• Phenotype• Chromosome• Locus• Allele• Diploid

• 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– 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

– 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

• Danny and Stephanie may be carriers, or they may not be, they are phenotypically normal

• Their kids could carry the allele, assuming they do

They got the looks, but I got the brains……..

• 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

• 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

• 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