Lecture Notes 5 & 6: Mechanisms of Evolution PDF

**LECTURE \#6: Mechanisms of Evolution** ***I. Molecular Basis of Genetics*** 1. **[Genome:]** the complete set of genes or genetic material present in a cell or organism. 2. **[Chromosome]**: = one DNA molecule + histone proteins 3. **[DNA]** - the molecule (double-helix, 5-C sugar +...

**LECTURE \#6: Mechanisms of Evolution** ***I. Molecular Basis of Genetics*** 1. **[Genome:]** the complete set of genes or genetic material present in a cell or organism. 2. **[Chromosome]**: = one DNA molecule + histone proteins 3. **[DNA]** - the molecule (double-helix, 5-C sugar + phosphate + nitrogenous base) 4. **[Central Dogma of Molecular Biology]**: DNA mRNA Protein / polypeptide (by way of tRNA and ribosomes) 5. **[Gene]** = discrete section of DNA molecule coding for a given product, either RNA or a protein. 6. **[Locus]** - position of a specific gene on a chromosome 7. **[Mutation]** -- change in the nucleotide sequence of genetic material (DNA or RNA) whether by substitution, duplication, insertion, deletion, or inversion. 8. **[Alleles]** - different forms of the same gene 9. **[Karyotype]** - number and appearance of chromosomes in the nucleus of a eukaryotic cell 10. **[Haploid -- 1]** set of genes (and chromosomes). 11. **[Diploid]** - 2 sets of genes (and chromosomes). i. \***[polyploid]** - \> 2 sets of genes/chromosomes. ***II. Terminology and Concepts of Genetics*** 1. **[Meiosis]** - - cell division resulting in 4 haploid cells from one diploid cell 2. **[Genetic recombination]** - new combinations (i.e., genetically unique individuals) from the same genes due to independent assortment and crossing over (*homologous* chromosomes exchanging parts). 3. **[Dominant]** - always expressed when present 4. **[Recessive]** - expressed only in the homozygous condition. 5. **[Genotype]** - sum of hereditary information that (in part) determines the structure and function of an organism. a. **[Homozygous]** - only one allele present (2 copies for a diploid organism) for a gene at a given locus. i. \*Note: populations can also be \"homozygous\" at a given allele if all (or virtually all) individuals have the same single allele. The term **[monomorphic]** is sometimes used when the common allele\'s frequency in the pop. is \>95%. 6. **[Heterozygous]** - more than one form of a gene at a locus. ii. \*Note: populations can also be heterozygous or **[polymorphic]** if the common allele\'s frequency in the pop. is \ a. **[Results in Non-adaptive] evolution** b. **[May affect course of evolution by natural selection, esp. during... ]** 5. **[Population bottleneck]** leads to significantly reduced genetic diversity, which will result in population extincttion when disastrous environmental disturbances occur 6. **[Gene flow]** -- the migration of genes into a population from other population via dispersal and interbreeding. 7. **[Non-random mating]** due to sexual selection, social structure etc. 8. **[Random mating]** - mating takes place at random with respect to the genotypes under consideration. The chance that an individual mates w/ another having a certain genotype is equal to the frequency of that genotype in the deme. Also refered to as \"*[panmixia]*\" or a panmictic pop\'l\'n. 9. **[Allele frequency]**: how to calculate 10. **[Hardy-Weinberg Law]** - an important \"null model\" in population genetics. States that for a *sexually reproducing, diploid* organism*,* both gene frequencies and genotype frequencies will remain constant from generation to generation in an infinitely large, random-mating population, in the [ABSENCE] of migration, mutation, and selection. Thus assumptions of this model are: a. *Population is infinite in size* b. *No Mutation* c. *No Migration* d. *No Natural selection* e. *Mating is random* \* THUS, sexual reproduction, Mendelian inheritance, etc. (recombination, crossing over\...) by itself, does NOT alter allele or genotype frequencies. \* If population departs significantly from H-W equilibrium values, then one of assumptions must be violated (e.g., perhaps natural selection is occurring, or migration) ***II. Forces of Evolution, esp. Natural Selection*** 1. **[Evolution]** - the change in the frequency of genetic traits in a population over generations (NOTE: populations evolve, [NOT] individuals). 2. **[Natural selection]** - *process* which causes changes in the frequency of genetic traits in a population over time through the differential survival and reproduction of individuals bearing those traits; Darwin\'s \"*survival of the fittest*\" (which more appropriately stated should be "*survival **[and reproduction]** of the fittest*". 3. **[The prerequisites of NS]** a. b. c. d. e. 4. **[Evidence for its existence]** a. Artificial selection -- human directed mating of domestic animals and food crops b. Antibiotic resistance in bacteria c. Peppered moth -- switch from white to black morphs, then back to white as industrial revolution progresses, then pollution controls reduce soot. 5. **[Agents of evolution other than NS]** 1. **[Mutation]** -- 2. **[Non]**-random mating 3. **[Genetic drift]** 4. Migration (=gene flow) 6. **[Habitat fragmentation (HF) and endangered species]** 5. HF convert large population into small, thus reducing population size and accelerating genetic drift 6. HF, if persisit for long time, interrupt gene flow, making small populations permenantly isolated 7. GD and lack of gene flow work together to increase inbreeding, resulting in reduced heterozygcity 8. Extinction can happen when NS occurs 7. **[Metapopulation]**