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

• 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

How DNA works

• Base pairs• Adenine• Thymine• Cytosine• Guanine• C -> G• A -> T

DNA and genes

• 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– 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

– 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…….

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

• 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 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