Lecture 7 and 8
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This 7 page Class Notes was uploaded by Avi Fox on Friday February 20, 2015. The Class Notes belongs to BIO 160 at University of Miami taught by Dana Krempels in Spring2015. Since its upload, it has received 89 views. For similar materials see EVOLUTION & BIODIVRSITY in Biology at University of Miami.
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Date Created: 02/20/15
Lecture 7 Heterozygosity and deleterious alleles Can be advantageous such as the sickle cell anemia example Measured with the hardy Weinberg People who were homozygous at their MHC major histocompatibility complex all vertebrae Encodes for MHC polypeptides and important players in the immune system loci and had HIV got AIDS faster and died compared to those who were heterozygous Captive big cats have a lot of inbreeding and are mostly homozygous so when they get infected with the parvovirus they usually die Purebred dogs cats and rabbits have a lot of congenital diseases due to homozygosity Hybrids individuals usually show a lot of heterozygosity Hybrid vigor the more closely related to the parents the less heterozygous Heterozygote advantage even though an allele can be harmful in the homozygous condition some can be a selective advantage in heterozygous condition Constant mutation some spots on the DNA mutate very frequently so when it gets weeded out new mutations occur Gene flow new individuals entering the population can bring it in when it wasn t harmful in their deme Natural selection is not instantaneous Allele might not be expressed before natural selection can act on it breast cancer comes after most women have already given birth so it is already passed down Age dependent expression Reproductive isolating Mechanisms Prezygotic Ecological isolation their geography overlaps but their ecological needs or breeding requirements differ For example one lives in fast moving streams and one breeds in permanent ponds Temporal Isolation they have different breeding seasons or different times of day Behavioral Isolation the 2 species have different complex breeding rituals Mechanical Isolation morphological differences that stop mating Orchid and bee only the bee can pollinate and only orchid can bring female Gametic Isolation the sperm and ova of the 2 species are chemically genetically incompatible Postzygotic Hybrid Inviability a zygote forms but the embryo dies after a few cell divisions Hybrid Sterility a viable hybrid is produced often more vigorous than either parent but cant reproduce Hybrid Breakdown later generations of hybrids have much lower fertility and eventually are selected out of the population Hybridization Between Species Species Reinforcement hybrids have lower fitness than both parents Reproductive isolation is maintained because the hybrids cant reproduce Species Fusion reproductive barriers weaken over time the 2 species share their gene pool fusing into a single species Species stabilityhybrid equilibrium hybrids are continually produced in the hybrid zone A narrow hybrid zone fosters constant hybridization with reduced hybrid survival Hybrid Speciation Hybrids may actually be reproductively superior to parent populations if they breed it can result in a new species Departure from HardyWeinberg 1 Mutation 2 Noninfinite population 3 Nonrandom assortative mating every individual in the population has equal chance to mate with the other sex 4 Migration 5 Natural selection Mutation 0 Adaptive more likely to reproduce O Maladaptive less likely to reproduce 0 Neutral doesn t matter either way Doesn t effect Darwinian fitness Can have no signi cant phenotypic change Silent mutation not the same as a neutral Doesn t change the identity of the encoded amino acid Nucleotide sequence can affect he secondary structure of DNA transferRNA s a silent mutation can affect the rate of translation of proteins containing that amino acid Codon bias A change in the availability of a particular amino acid during translation can have a profound effect on phenotype Small phenotypic effect may not affect fitness Major phenotypic effect Single mutation can result in resistance to pesticide or antibiotics Single mutation can be lethal mostly homozygous recessive Single mutation can cause reproductive isolation Japanese land snailmechanical isolation Classical model in any given pop Oneallele functions better tan the others at a particular locus Natural selection will drive the pop to a higher proportion of this allele Wild type phenotype most common phenotype for a particular trait in a population Mutant type any allele other than the wild type The balancing Selection Model Theodosius Dobzhansky coined the term balancing selection an allele might be maladaptive under certain conditions can be maintained in a population by having an advantage under different conditions Heterozygote advantage 0 Sickle cell anemia 0 Male homosexuality Frequencydependent selection selective pressure against a particular allele changes with that allele s relative frequency in the population search image when a predator develops knowledge of what certain prey looks and smells like then the predator sensory systems develops sensitivity and preference for its features Increases efficiency in finding prey and can contribute to frequency dependent selection 0 Positive selection favor the phenotype when its more common in the population Batesian mimicry where a harmless species mimics the appearance of a poisonous species By doing this the predator will try to avoid them 0 Negative selection favors the phenotype when it is more rare in the population The Neutral Theory of Molecular Evolutions Kimura proposed that most diversity at the genetic level is due to random genetic drift of neutral mutant alleles not natural selection Go along with the ow but can have drastic effect if they are in a small population and become fixed 2Infinitely large population size If its not large you have a sampling error Genetic drift it is the cause of sampling error all by chance Founder effect small subset of population moves to a new location The small size won t always represent the allele frequencies of the whole population and some alleles will be present in greater quantities More likely that genes will become fixed Bottleneck effect big population and everyone but a small subset get wiped out The allele frequencies wont represent the parent population A small population will evolve much quicker if its all done by random chance 3 Random mating if a every member of the population has an equal chance of mating then the frequencies shouldn t change Product rule the likelihood that a certain mating will occur is equal to the product of their frequencies Nonrandom mating Positive assortative mating individuals of similar genotypephenotype mate together significantly more often Results in greater homozygosity Inbreeding Negative assortative disaasortative mating opposite attract Increases heterozygosity Outbreeding Nonrandom mating Inbreeding change allele frequencies 4No migration Gene ow movement of genes that take place between populations or demes Spreads alleles that came about with mutation it has homogenizing effect if a recipient population is small relative to a donor population increases the effective size of a population lack of gene ow can cause speciation Cohesive species whose demes tend not to become reproductively isolated Coyote and timber wolf lineages remain separate but they still sometimes hybridize Forces that drive evolution large population random mating and migration have to do with population size small pop means greater likelihood of nonprepresntative sample of genes in the next generation assortative mating segregates subsets of genes into smaller interbredding population lack of migration results in smaller population size Migration restores large pop s1ze 5Natural selection Bene cial Deleterious Neutral It s all about context Natural selection is directed 1 Overproduction 2 Variability physically variable and its heritable 3 Competition limited resources 4 Differential reproduction those best suited win Darwinian evolutionary fitness measure of the proportion of an individuals genes it gives to succeeding generations Fitness coefficient W is an expression of the adaptive value of a particular genotype relative to other genotypes The one who produces the most get an arbitrary value of 1 just comparisons Selection coefficient 8 measure of selective pressure against a particular genotype 1 W Sexual selection its based upon an individual s relative ability to attract and mate with members of the opposite sex Sexual selection is most likely to change allele frequencies when there is competition for mates Sexual dimorphism differences between males and females sexual selection one sex competes directly for mates males defending a group of females from other males Ones with traits that let them win mates will mate more often John Maynard Smith Sneaky fuckers studying deer and saw that as the males would fight for the females some males would stay on the side and quickly mate with the females as the other males fought sexual selection mate choice one sex is choosy in selecting their mates Peacocks feathers Lions Mane the darker the mane the more attractive and healthy he is Carotenoid production in birds parasites can cause birds to not display as bright redorangeyellow carotenoid pigments The females choosing bright colored males are getting a signal of health and genetic quality Sexy son hypothesis females who choose attractive males will produce betterlooking sons Handicap principle ornamentation is an honest signal of health and vigor It s a compromise between danger and sexual advantage Peacock males have large brightly colored feathers to advertise to females that he is genetically superior Effects of natural selection Stabilizing selection Directional Selection Disruptive diversifying selection there is a disadvantage to be at the center of the curve So the 2 far sides of the curve are advantages Natural Selection Doesn t make perfect organisms Natural selection acts only on polymorphism that already exist works on traits that the population has Mutations are random don t evolve because organisms need or want them It only works only on traits that already exist mutations work on existing structures Doesn t create new ones Natural selection results in traits that are sometimes compromises traits can be adaptive for one niche but maladaptive for another Random events govern evolution Lecture 8 origin of species Macroevolution origin of species Speciation is the separation of 2 previously interbreeding populations into 2 populations that can no longer mate to produce fertile viable offspring Species concept Morphological typological species concept Oldest a species is a group of organisms that look similar Have a common morphology Species are essentially static and non changing Biological species concept Mayr a species that interbreeds naturally and reproductively isolated from other such groups Evolutionary species concept Simpson a species is lineage evolving a separately from others and with its own unitary evolutionary roles and tendencies EcologicalRidley a set of organisms occupying the same ecological niche No two species can occupy the same ecological niche the species and how it responds to both abiotic and biotic factors in its environment Cladistics phylogenetic species concept the smallest group of individuals descended from a common ancestor Macroevolution the genesis of reproductively isolated populations from an ancestral population Speciation takes time at least 1 generation Populations exist in various stages of Speciation at any given time Living extant populations are undergoing microevultionary changes Incipient species species on the verge of becoming separated Anagenesis the conversion of an entire population to a recognizably different The cladist doesn t consider this Speciation Cladogenesis Speciation when one ancestral population splits into 2 Adaptive radiation many cladogneiss events have taken place from a single ancestral species One ancestral species gave rise to new species that had different selective pressures that gave rise to new species This can be driven by mutation migration assortative mating genetic isolation andor natural selection Ecological niche describes all that species ecological requirements what it eats where it lives and nests and all its interactions with the biotic and abiotic factors No 2 species can have the same ecological niche Gauses s Law Competitive Exclusion Principle 2 species cannot coexist if they use the exact same resources Resource partitioning in order to avoid competition species must adapt and specialize dividing a common resource so that each competing species use only a portion of that resource Ex the warblers have 5 different yet similar species that forage on different parts of the evergreen forest There can be some overlap but they need regions Where only they forage Character displacement physical changes associated With this resource partitioning Color changes beak length Honey creepers 40 different species came from a finch like ancestor that each has a specialized bill shape and size Galapagos nches all have different resources but all came from a single species Poison dart frogs aposematism coloration to warn predators get the poison from their diets of ants Modes of speciation Allopatric other fatherland Sympatric together Allopatric Speciation single population is divided into 2 by geographic barriers Doesn t always happen but if they become differentiated enough that they can no longer interbreed they have undergone allopatric speciation Peripatric Speciation a small subset of a large population becomes isolated and over time become reproductively isolated Special case of allopatric speciation Polar bears evolved from browngrizzly bears Now know that polar bears came from brown Irish bears As climate changes interbreeding is occurring more often Parapatric Speciation occurs on a larger scale large numbers of a population gradually becoming differentiated along the range of the population Becomes a gradation
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