Download Genetics

Genetics
Genetics and Behaviour
• For behaviour to be affected by natural selection,
some variation in behaviour must be inherited
– If not, the characteristics could not be passed on right?
– Otherwise, could contribute to fitness, but could NOT
evolve
• Remember, only heritable, genetically transmitted
variation can be affected by selection
Introduction
• ‘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
How DNA works
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Base pairs
Adenine
Thymine
Cytosine
Guanine
C -> G
A -> T
DNA and genes
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Genes encode proteins
DNA -> RNA
RNA -> Proteins
Proteins -> phenotype
Environment -> genes
– Though some genes are less
responsive than others
An Example
• Human Ocular cutaneous albinism
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I wonder where that example came from…..
Single gene for the production of melanin
A – normal
a - bad
Dominance / Recessive relationship
AA, aA, Aa all lead to normal, aa leads to me
• Leslie and Rick
• 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…….
Partial Dominance
• Telleogryllus oceanicus and
T. commodus
• Males call to attract mates
(function)
• Song is species specific
• Male hybrids produce
hybrid song
• Female hybrids prefer
hybrid song.
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 why are there different alleles?
• On the surface, if some allele is better than
some other, why does it not replace all other
alleles?
• Neutral alleles?
• Environmental fluctuation
• Heterozygote superiority
• Frequency dependent selection
• And, of course, mutation
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