Principles of Biology II
Principles of Biology II BIOL 2108
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This 6 page Class Notes was uploaded by Colby Frami on Monday October 12, 2015. The Class Notes belongs to BIOL 2108 at Georgia Southern University taught by Daniel Gleason in Fall. Since its upload, it has received 60 views. For similar materials see /class/222025/biol-2108-georgia-southern-university in Biology at Georgia Southern University.
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Date Created: 10/12/15
Chapter 23 The Evolution of o What is evolution in genetic terms o Gene Pools and Wield lquot bhanges in proportions of alleles present for a particular trait in a population across generations l Populationl group of individuals of the same species living in the same area and capable of interbreeding and producing fertile offspring Gene pool all the alleles for all the gene loci present in all individuals ofa population at any one time o Where does genetic variation come from Two processes produce the variation that exists in gene pools o mutation o sexual recombination Mutation Changes in the nucleotide sequence of DNA Cause new genes and alleles to arise lMost arise in somatic cells and are lost PUnt Muratans o A change in one base in a gene o lUsually harmless becausd 0 occur in noncoding regions of DNA 0 redundancy in DNA code Muratans ThatAter Gene Number 0 Sequence o Chromosomal mutationsthat delete disrupt or rearrange many loci are typically harmful o Duplication of large chromosome segments nearly always harmful 0 Not always true for smaller pieces which may enhance variation lMutaton Rates l o Mutation rates low in animals and plants 0 average is one mutation in every 100000 genes per generation o Mutations rates lower in prokaryotes 0 but short generation times allow rapid accumulation of mutations t 1 and hair color are controlled by tiple loci not by individual locus s rneans there rnust be variation among a Comment 2 Hog Population 2 alleles Blong bristle length bshort bristle length ndividuals are diploid which gives the homozygous dominantIon bristles heterozygouslong bristles and homozygous recessiveshort bristles ment 3 Populations do thave to be physically separated Comment 4 mutations that occur in cells other than the sex cells skin cells cancer be ifthey do not occur in sex ee11s they cannotbe passed onto ones offspring Comment 5 BUT Igni c re sickle cell trait pacts on phenotype do occur t 6 ans are otten used as indicator species because they are Very sensitive to changes in the mvironment chemically and such Sexual Recombination o Shuffles existing alleles creating unique combinations 0 Crossing over dprophase ID Comment 7 ofmeiosis 0 Independent assortment metaphase I Fertilization o How do we measure evolution 0 Hardy Weinberg equation o The HardyWeinberg Theorem o Sets baseline for a population that is not evolving o Basic premise o If only Mendelian segregation and recombination are at work in a population then the frequencies of alleles and genotypes in the population should remain constant from generation to generation 0 Mendelian inheritance preserves genetic variation in a population o Preservation 0M ee Frequencies o In a population where gametes contribute to the next generation randomly bliele 39 Ivvill not change C zmment8 o HardyWeinberg equilibrium describes a population in which 51 F changingaswell o random mating occurs o allele frequencies do not change over time o HardyWeinberg Based on Probabilities o lfflip 1 coin o Probability of getting heads 50 05 p o Probability of getting tails 50 05 q o lfflip 2 coins o Probability of getting 2 heads 05 x 05 025 p2 o Probability of getting 2 tails 05 x 05 025 q2 o Probability of getting 1 heads and 1 tails 0 heads rsg tails second 05 X 05 pq o tails firsL heads second 05 X 05 pq o 05 X 05 05 X 05 05 pq pq 2pq o HardyWeinberg Theorem p2 2m q2 o where p and q represent frequencies of different alleles so o p2 2pq and q2 represent frequencies of different genotypes o Remember p q 1 o Why is HardyWeinberg Important 0 Deviations from HardyWeinberg Equilibrium indicate evolution is place Practice Sea Star Populations o 100 individuals 36 are red 64 are purple Red R o Purple r o lfthe population is at HW Equilibrium o What is ql red 036 K o iWhatisplpurple064 WEI o lfthe population is at HW Equilibrium what isthe p2 2pq q2 1 initially nd q2 be those are your homozygous essive o Frequency of homozygous recessive Number l q2 se1oo Comment 11 112 36100 o Frequency of heterozygous Number Fm o Frequency of homozygous dominant Number o Check your work E 2pq 72 1 o Come back in 100 years now 400 sea stars present 200 red 200 purple Has evolution taken place Practice Mouse Populations o 500 individuals 255 are long tail 245 short o Long L o short l o lfthe population is at HW Equilibrium o What is d o What is o How many heterozygotes o Commans for Hard y Wenberg Equ brum o HardyWeinberg theorem describes a hypothetical population In real populations allele and genotype frequencies DO change over time o The five conditions for nonevolving populations are rarely met in nature 0 No Mutations By altering alleles or in largescale changes deleting or duplicating entire genes mutations modify the gene poo Random Mating If individuals mate preferentially within a subset of the population such as their close relatives inbreeding random mixing of gametes does not occur and genotype frequencies change No Natural Selection Differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies 0 Extremer large population Size The smaller the population the more likely it is that allele frequencies will uctuate by chance from one generation to the next genetic drift 0 No gene ow By moving alleles into or out of population gene ow can alter allele frequencies o Ducks on the pond Chapter 23 The Evolution of Populations Part 2 o Popuaton Genetcs and Human Heatz o We can use HardyWeinberg to estimate the of the human population carrying the allele for an inherited disease o Phenylketonuria PKU recessive trait o Occurrence 1 per 10000 births o What is the chance that you are a carrier o Genetic counseling o What are the agents of change in populations o Three major factors alter allele frequencies and bring about most evolutionary change Natural selections Genetic Drift 0 Gene Flow o Natural Selection o Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions o Summary of Natural Selection o Heritable variation o Differential reproductive success due to interactions with environment o Adaptationsthat result in better match to environment increase in frequency in population overtime o If environment changes overtime natural selection may result in adaptation to the new conditions o Genetic Drift o The smaller the sample the greater the chances of deviation from a predicted result o The unpredictable fluctuation in allele frequencies from one generation to the next o Genetic drift tends to reduce genetic variation through losses of alleles Fig 238 o Genetic Drift T7e BartenecE ect o Sudden change in the environment that drastically reduces the population size o Resulting gene pool may no longer reflectthat of original population o Understanding the bottleneck effect increases understanding of how human activity affects other species o Example Florida panther o Genetic Drift T7e FounderE ect o Occurs when a few individuals become isolated from a larger population o Gan affect allele frequencies in a population 0 Cultural isolation nonrandom mating o Polydactyly more common in Amish communities in US than in general population o Gene Flow o Genetic additions or subtractions from a population resulting from movement of fertile individuals or gametes Tends to reduce genetic differences among populations over time o Fig 2312 BentGrass Bent grass tolerant of copper in abandoned mine Why also tolerant in pasture Sometimes gene flow may prevent adjacent populations from fully adapting to their environment o KEY POINT o Natural selection is the My mechanism of adaptive evolution Comment 12 Natural selection accumulates and maintains favorable genotypes in a population becau emeindmdualswim mefavmblegmtypes are going to be the ones to iepiodnee o Types of Natura Select0n Fig 231 3 m t 13 mmen I vors those individuals ylho have extreme Variation lDirectional selection favors individuals at one end of the phenotypic range Disru ptivd selection favors individuals at both extremes of the phenotypic range Cumberland Island horses being tolerant ofsalt o Btabilizingi election favors 39 quot varianm and acts against extreme phenotypes like directional selection favors the extremes traits in a population Disruptive selection differs in that sudden changes in the environment creates a sudden forces favoring that extreme Comment 16 evois the nonn the common average traits in a population o Sexual Selection o Natural selection for mating success Can result in sexual dimorphis marked differences between the sexes in secon Comment 17 the two sexes are extremely different sexual characteristics lntrasexual selection is competition among individuals of one sex for mates ofthe opposite sex o Female choice may be based on the showiness of the male lntersexual selection occurs when individuals of one sex usually females are choosy in selecting mates
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