Lecture 4 Modern Evolutionary Theory DNA - Deoxyribonucleic acid Studies during 1930's proved that chromosomes made up of DNA What it does is make proteins- strings of amino acids (20 different kinds of a.a.) Watson and Crick and the discovery of the shape of DNA- double helix 1950's Two backbones twisted around each other Base pairs connect as "steps" in center Four bases; A, G, C, & T A connects to T and G connects to C How DNA works Double helix allows "unzipping" of DNA During replication, new bases connect to each side of old; result 2 strands During protein synthesis, only part unzips messenger RNA copies gene goes out of nucleus where it connects with transfer RNA tRNA carries amino acids to ribosome which connect to make a protein sequence of 3 bases equals a codon- codes for a particular amino acid 64 possible combos of base pairs; allows redundancy & stop codes Mutation occurs when a base is changed (point mutation) Different base changes codon Since redundant, may not change amino acid If does, changes protein sometimes small effect, good or bad sometimes large effect if in regulatory gene Other ways genetic code can change Crossing over of chomosomes & exchange of DNA Inversions of DNA sequences w/in a chromosome Additions and subtractions of DNA to chromosomes Adaptation Changes in a species body and/or behavior to suit its lifestyle and /or habitat Niche- ecological term for a particular way of making a living Diet- carnivore, herbivore Habitat- terrestrial, arboreal Behavior- pursuit hunting, ambush hunting Body parts have functions; shaped to fit function Darwin's finches Skin color, lactose intolerance in humans Phylogeny A "family tree" based on physical and/or behavioral traits Primitive vs derived traits Homologous vs analogous traits Population genetics and speciation Interbreeding populations of a species Where evolution occurs- changes in allele frequencies Total all genes in a population called the "gene pool" Changes in gene frequencies Mutations- introduces new traits into a population Gene flow- transfer of alleles between populations Genetic Drift- random events that change frequencies (including "founder effect") Speciation- when enough change has occurred that different populations are no longer the same species- often through reproductive isolation Gradualism When a slow accumulation of changes leads to speciation Adapting to conditions of particular enviro or to conditions that change slowly Happens throughout a population Punctuated Equilibrium Sudden changes giving rise to new species Mutations with large effects or rapidly changing environment Happens to a split-off population, often by geographic barrier Most of time Natural Selection "fine-tunes" to particular environment Example putting it all together- Sickle-Cell Trait Hemoglobin (in Red Blood Cells) has two pairs of proteins (2 alfa & 2 beta chains) Since genes are paired, one chain of each pair inherited from each parent Normal HbA (BetaABetaA) Beta chain 146 amino acids long Position 6- Glutamic Acid; codon CTC Mutation T>A; codon CAC, Valine Hemoglobin's job is to take up and release oxygen When both Beta chains have mutation (called HbS; BetaSBetaS) When oxygen released, cells "sickle"; become oddly shaped Valine causes Hb to stack up and make Red Blood Cells rigid Sickle cells then clog capillaries, get destroyed Many health effects from anemia; too few RBC's; die at an early age Yet Sickle-Cell trait very prevalent in certain populations More than mutation alone could account for Something must be selecting it- but not homozygous, heterozygous (BetaABetaS) Distribution HbS coincides with distribution of malarial parasite Plasmodium falciparum, a very nasty form of malaria Heterozygous, having one Beta chain mutated and one normal Survive malaria better than homozygous Malaria carried in RBC Reproduce till fill cell, then burst out and infect other RBC's If one Beta chain HbS, Sickles easier when parasite grows because parasite uses up oxygen Sickled cells get destroyed, removing parasite from system quicker In malarial areas, homozygous people either die from malaria or from anemia, heterozygous survive This is called a Balanced Polymorphism