Transcript 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 • • • • • • • 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 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 • • • • • • 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