| VI: Genetics & Evolution |
| Genotype vs. Phenotype |
| Genotype = the genetic makeup of an individual organism | |
| Phenotype = the observed characteristic of the organism | |
| Through interaction with environment, a genotype is expressed in a phenotype |
| Ontogeny |
| Genotype Space vs. Phenotype Space |
| Selection |
| Selection operates on the phenotype, not the genotype | |
| Selection of genotypes is indirect |
| ÒCentral DogmaÓ of Genetics |
| ÒThe transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible.Ó | ||
| Francis Crick | ||
| A hypothesis (not a dogma) | ||
| ÒNewÓ Lamarckism: Òjumping genesÓ and reverse transcription | ||
| Essentialism vs. ÒPopulation ThinkingÓ |
| Essentialism: each species has a fixed, ideal ÒtypeÓ | ||
| actual individuals are imperfect expressions of this ideal | ||
| species have sharp boundaries | ||
| the type is real, variation is illusory | ||
| Population thinking: a species is a reproductive population | ||
| only individual organisms exist | ||
| species have blurred boundaries | ||
| species are time-varying averages | ||
| variation is real, the type is an abstraction | ||
| The Second Law of Thermodynamics |
| The Second Law and Open Systems |
| Nonequilibrium Thermodynamics |
| Classical thermodynamics limited to systems in equilibrium | ||
| Extended by thermodynamics of transport processes | ||
| i.e. accounting for entropy changes when matter/energy transported into or out of an open system | ||
| Flow of matter/energy can maintain system far from equilibrium for long periods | ||
| Hence, nonequilibrium thermodynamics | ||
| An Energy Flow Can Create Structure |
| BŽnard Convection Cells |
| Persistent Nonequilibrium Systems |
| If flow creates system so structured to maintain flow | ||
| then positive feedback causes nonequilibrium system to persist indefinitely | ||
| but not forever (2nd law) | ||
| Systems we tend to see are those most successful at maintaining nonequil. state | ||
| Applies to species as well as organisms | ||
| Evolution |
| Slide 15 |
| Fitness |
| 1st approximation: the relative ability of an individual organism to optimize the energy flow to maintain its nonequilibrium state long enough to reproduce (survival fitness) | ||
| 2nd approximation: reproductive fitness = the relative efficiency at producing viable offspring | ||
| of oneself (exclusive fitness) | ||
| of oneself or close relatives (inclusive fitness) | ||
| ÒSelfish GeneÓ |
| An organism is a geneÕs way of making more copies of itself | |
| A gene (or collection of genes) will tend to persist in a population if they tend to produce physical characteristics & behavior that are relatively successful at producing more copies of itself | |
| Nevertheless, it is physical organisms (phenotypes) that confront the environment |
| Complicating Factors |
| Individual genes influence multiple characteristics & behaviors | ||
| Genes are not independent | ||
| ÒFitnessÓ is in the context of a (possibly changing) environment including: | ||
| conspecifics | ||
| coevolving predators and prey | ||
| Conclusion: beware of oversimplifications | ||
| keep entire process in mind | ||
| Example Effects of Single Genes |
| Butterfly Eyespots |
| Major changes within 6 generations | |
| May lead to patterns not seen in previous generations |
| Two Populations of Astyanax mexicanus |
| Two populations of one species | ||
| Regulation of one gene (controlling head development) | ||
| eyes, smaller jaws, fewer teeth | ||
| blind, larger jaws, more teeth | ||
| Human Fear Response |
| Single Gene Affecting Human Fear Response |
| Two alleles for gene: | ||
| short allele Þ greater anxiety response to angry or frightened faces | ||
| long allele Þ lesser response | ||
| Gene encodes transporter protein, which carries serotonin back into neuron after release | ||
| Short allele produces 1/2 amount of protein | ||
| Accumulating serotonin affects neighboring cells | ||
| Human vs. Rat Cortex |
| Human cortex relatively larger | |
| Also more structured |
| Experiment |
| Problem: How do organs know when to stop growing? | |
| Genetically engineer rats to express a mutant form of protein (b-catenin) | |
| More resistant to breakdown, \ accumulates |
|
| Spurs neural precursor cells to proliferate |
| Results † normal |
| Results † normal transgenic Þ |