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Evolution.docx

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Department
Biology
Course
Biology 1201A
Professor
Richard Gardiner
Semester
Fall

Description
Evolution: What is a theory?  An untested idea or opinion (speculation)  An explanation of a set of natural phenomena, based upon proven or testable hypothesis and observation Early evolution thought:  Aristotle- the scala natura- that living thing are on a scale. More complex are more godly  Carl Von Linne-  Le comte de Buffon-  Was static classification and characterization Georges Cuvier:  Believed in the fixity of species  Changes in fossil forms a result of repeated catastrophic events and new creations Jean- Baptiste Lamarck  Species evolve to better fit their environment  Through an organism’s lifetime, certain traits would be used and certain wouldn’t be. This causes a change in trait through reproduction. Charles Lyell  Natural agents currently at work have been at work throughout Earth’s history.  World has been hanging slowly overtime Charles Darwin  Evolution by natural selection  Species change gradually through time due to interactions between individuals traits and their environment Natural Selection: Evolution is necessary for evolution Variation must be heritable Survival/reproduction must vary according to traits. Differential survival and reproduction of individuals in a population due to current environmental influences. Heritability- proportion of phenotypic variation in a population due to variation in genes H= Vg/ (Vg+Ve) Heritability= (Variation due to genotype)/(Total variation in phenotype) Evolution by natural selection is observable:  Antibiotic resistance in bacteria  Pesticide resistance in insects  Heavy metal tolerance in plants  Break size in Darwin’s finches Fitness- is the degree to which an individual contributes offspring to future generations  Ability to pass on allele In a population of squirrels, black individuals (BB) have an absolute fitness of 4, brown individuals (Bb) have an absolute fitness of 6 and blondies (bb) have an absolute fitness of 2. Relative fitness= (absolute fitness of individual)/(max. absolute fitness of population) Fitness (bb) = 2/6= 0.33 Adaptations Traits that increase the probability that an individual with that trait will survive or reproduce in a particular environment Ex. Thorns on roses for defense Can change behavioral -> school of fish. Constraints (limitations) on adaptations:  Available variation for selection to act upon  Changing environments over time  Conflict between selection pressures (Micro)evolution Small- scale changes in genetic make up of a population Hardy Weinberg Principle: Part 1: Knowing if something (an allele) is dominant doesn’t tell us if it is common (or rare) Knowing an allele is common, doesn’t tell you if it is dominant or recessive Phenotype ratios for populations aren’t “nice” (ei not 3:1, 1;1) Frequencies stay consistent over time. Part 2: Allele frequencies don’t change overtime Genotype frequencies in a population can be predicted from allele frequencies. Allele Frequency: Allele frequencies give expected offspring genotype frequencies based on probability. Genotype frequencies of offspring:  P x P=p^2  2(PXQ)= 2pq  QXQ= q^2 Assumptions: 1. No selection  All phenotypes had equal fitness 2. Random mating 3. No mutations 4. No successful immigration or emigration  No “gene flow” 5. No random event  No genetic  Assume large population BB Bb Bb Mice 422 455 123 B 2X422 1X455 0X123 =844 =455 b 0X422 1X455 2X123 =0 =455 =246 Total B= 844 + 455= 1299 Total b= 455 + 246= 701 F(B)= #B/total allele =1299/200 =0.6495 Evolutionary Mechanisms: Origins of genetic variation The paradox of genetic variation Mechanisms of evolution:  Mutation  Selection  Sampling drift  Gene flow  Non-random mating  Conforms to HWE- not evolving Genetic variations: Caused by:  Mutations- translocations, deletion, insertions, duplications  Mutations are rare, random errors  Deleterious mutations- negative- more common  Advantageous mutations- positive  Some mutations are selectively neutral- Not only bad, some positive and negative benefits from mutation  Homeotic genes regulated the expression of other genes  Mutations in regulatory genes for development can generate new body shapes  Chromosomal mutations- polyploidy, trisomy etc.  Random mating  Random fertilization  Crossing- over- genetic recombination  Open populations- new alleles entering  Independent assortment The paradox of genetic variation Shouldn’t selection reduce genetic variation?  Advantageous mutations should ‘fix’ in a population (fixation)  Genetic variation should be temporary  Should weed out bad, leave us only with good Would assume its only one allele present Ex. Only thick shell present  “fixed” Types of Selections: Directional In directional, the genes all move to one direction therefore less variation within population Fitness increases with phenotype value Mean phenotype changes overtime One extreme favored, other extreme disfavored Stabilizing Maintains middle phenotype, cutting down the extreme phenotypic populations. Intermediate phenotype has highest fitness Mean phenotype maintained, variance reduced Example: Before babies were born to be too heavy or too light in weight. Due to modern medicine the variation in fitness causing babies to be born within 7-8 pounds which is healthier Disruptive Phenotype spreads out across a population Extreme phenotypes have highest fitness Does not alter mean phenotype, variance increases Intermediates disappear over time. Example: Good to be big or small, no advantage to being medium. Heterozygous have higher fitness than either homozygote  Known as heterozygote advantage Sample Drift Change in allele frequencies due to the effect of chance in small sample  Random in small populations. Unpredictable changes in the short term Should cause fixation in the long term  Fixed to one allele frequency of 1.00 What causes a change in genetic make up due to sampling? 1. Random chance during reproduction 2. “Bottleneck events” that reduce population size  Kill off individuals leaving random samples  Survivors determine allele frequency 3. “Founder effects” that create new populations from a small sample.  Just by random chance founders have different allele frequency therefore, mating new population when they mate Gene Flow The movement of alleles from one population to another  2 populations diff. in allele frequencies Tends to equalize allele frequencies among populations Maintains genetic variation within populations  brings “striped” allele with them therefore, variation increases, keeps alleles coming in , despite selection working against it. May oppose local selection pressures Non- random mating  Care about who mating with based on phenotypes Individuals select mates based on phenotype 1. Assortative mating  Like maters with like  Promotes inbreeding and homozygousity 2. Disassortive mating  Opposites attract  Greater heterozygousisty Disrupts genotype frequencies, but not allele frequencies Increases homzygosities- allele frequency not change, phenotype changed  #Evolving Sexual Selection Advantages Disadvantages Lottery model -Investing something into somebody else  Sexual reproduction increases the -Trusting taking 50% of genes from likelihood that some offspring partner will be appropriately equipped to -Can contact STDs survive -Busy having sex  Not focusing on predators  Buying 5 lottery tickets, better odds winning when buying 5 -It screws up what your offspring looks tickets all different numbers vs 5 like if you want them to look like you tickets all same numbers -If you don’t find a mate, it takes a long  We have different phenotypes time to find a mate when it is sexual reproductions,  Waste of time therefore carrying offspring, -Not guaranteed a mate which increases chances that one  May cost fitness offspring may survive Particular phenotype that is 100% good in that environment, wouldn’t want to risk changing! But we do see sexual reproduction in all environments because it is better than asexual reproductio
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