Chapter 23 24 and 25 Notes
Chapter 23 24 and 25 Notes BIOL 2601 - 01
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BIOL 2601 - 01
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Date Created: 11/18/15
Chapter 23 An Introduction to Evolution The Theory of Evolution Evolution heritable change in one or more characteristics of a population or species from one generation to the next Microevolution changes in a single gene in population over time Macroevolution formation of new species or groups of species History of the Theory of Evolution Empirical thought relies on observation to form idea or hypothesis George Buffon life forms change over time J canBaptiste Lamarck some animals change While others don t Living things evolved toward perfection Inheritance of acquired characteristics Uniformitarianism hypothesis slow geological process lead to substantial change Thomas Malthus only fraction of any population will survive and reproduce Charles Darwin Theory shaped by Geology Economics and Voyage of the Beagle Voyage of the Beagle 18311836 Noticed distinctive traits of island species Where that could better exploit their environment ex Galapagos Island finches specialized feeding strategies Timeline Mid 1840s formulated theory of evolution Spent additional years studying barnacles 1856 began writing book 1858 Alfred Wallace sends Darwin manuscript with many of same ideas published papers together 1859 Darwin s 0n the Origin of Species published Descent with Modification Evolution based on 1 Variation Within a given species a Traits heritable b Genetic basis not yet known 2 Natural Selection a More offspring produced than can survive b Competition 0 Individuals with better traits survive and reproduce Evidence of Evolutionary Change Fossil record Biogeography Convergent evolution Selective breeding Homologies anatomical developmental and molecular U PP P Horses case of how evolution involves adaptation to changing environments Fossil record adaptive changes in size foot anatomy and tooth morphology Changes attributed to natural selection from changes in global climate Dense forests replaced with grassland Run faster eat tougher food Biogeography study of geographical distribution of extinct and modern species Isolated continents and island groups evolved their own communities Endemic naturally found only in particular location Evolution of major animal groups correlated with known changes in distribution of land masses Convergent Evolution two different species from different lineages shown similar characteristics because occupy similar environments EX Giant anteater and echidna long snouts and tongues aerial rootlets clinging antifreeze proteins in different very cold water fish Selective Breeding programsprocedures designed to modify traits in domesticated species artificial selection Darwin in uenced by pigeon breeders Nature choose parents natural selection breeders choose in artificial selection desirable phenotypes Made possible by genetic variation Homology fundamental similarity due to descent from common ancestor 1 Anatomical set of bones of modern vertebrates undergone evolutionary change a Homologous structures common ancestor b Vestigial structures no apparent function but resemble ancestors 2 Developmental differ as adults that bear striking similarities during embryonic stages a Gill ridges in human embryos evolved from aquatic animals with gill slits b Human embryos have long bony tails 3 Molecular similarities at molecular level evolved from ancestor DNA to store info Certain biochemical pathways found in all or nearly all species same type of gene found in diverse organisms p53 9role in preventing cancer P PP Molecular Processes that Underlie Evolution Homologous genes two genes derived from same ancestral gene Orthologs occur in separate species Reveal molecular details of evolutionary change Two sequences may be similar but not identical independent accumulation of random mutations Paralogs homologous genes within single species Gene duplication can lead to gene family two or more paralogs within genome of single organism EX Globin genes expression at different times or different tissues Horizontal Gene Transfer exchange of genetic material among different species Can transfer 1 from prokaryotes to eukaryotes and vice versa 2 between prokaryotes 3 between eukaryotes Widespread among bacteria and surprisingly common Evolution also occurs at genomic level changes in chromosome structure and Compare three largest chromosomes in humans and apes Similar due to close evolutionary relationship Humans 1 large chromosome 2 Apes 2 separate chromosomes divide chromosome 2 Chromosome 3 very similar orangutans large inversions Chapter 24 Population Genetics Genes in Populations Population Genetics study of genes and genotypes in population Want to know extent of gene variation Gene variation related to phenotype Gene P0019 all of the alleles for every gene in population Study gene variation within gene pool and how variation changes between generations Variation in alleles between generation Population group of individuals of same species that occupy same environment and interbreed Wide geographic range and divided into discrete populations HardyWeinberg Equation p2 2pq q2 1 p29 genotype homozygote CRCR 2pq9 genotype heterozygote qz genotype homozygote CWCW Conditions 1 No new mutations 2 No natural selection 3 Population is large 4 No migration between different populations 5 Random mating In reality no population meets these conditions Microevolution changes in population s gene pool from generation to generation Change because Introduce genetic variation Evolutionary Mechanisms that alter allele natural selection random genetic drift migration nonrandom mating Natural Selection beneficial traits are heritable become more common in successive generations Overtime natural selection results in adaptations Reproductive success likelihood individual contributing fertile offspring to next generation attributed to two categories of traits certain characteristics make organism better adapted traits directly associated with reproduction Modern Description 1 Within a population allelic variation arises from random mutations that cause differences in DNA 2 Some alleles encode proteins which enhance individual s survival or reproductive capacity 3 Individuals with beneficial alleles more likely to survive and contribute alleles to next generation 4 Over the course of many generations allele frequencies of many genes may change thereby altering characteristics of a population Natural Selection Patterns 1 Directional Selection individuals at one phenotype extreme have an advantage a Initiators new allele with higher fitness and prolonged environmental change 2 Stabilizing Selection favors individuals with intermediate phenotypes being average a Ex Clutch size too many eggs and offspring OR too few eggs 3 DisruptiveDiversifying Selection favors two or more different genotypes that produce different phenotypes not being average a Likely in heterogeneous environments b Members freely interbreed 4 Balancing Selection maintains genetic diversity a Balanced polymorphism two or more alleles kept in balance and maintained in population over many generations b Two common ways i Single gene Heterozygote favored ii Negative frequencydependent selection rare higher fitness Sexual Selection form of natural selection where certain traits make it more likely for individuals to find or choose mate males more intensely than females in many species 1 Intrasexual selection between members of same sex males directly compete for mating 2 Intersexual selection between member of opposite sex female choice showy characteristics for males Explain traits that decrease survival but increase reproductive success 4 Females prefer brightly colored males a Few predators males brightly colored balance between sexual selection b Predators abundant not many brightly colored males predation 9 Genetic Drift changes allelic frequency due to random chance unrelated to fitness Favors loss or fixation of an allele frequency reaches 0 or 100 Faster in smaller populations Bottleneck population dramatically reduced and then rebuilds Randomly eliminates members Survivals may have different allele frequencies from original population Small population allele frequency drift substantially New population less genetic variation Founder Effect small group of individuals separates from larger population and establish new colony Small population less genetic variation and allele frequencies may differ from original Neutral Theory of Evolution NonDarwinian Neutral variation much of variation caused by genetic drift Genetic variation accumulation of neutral mutations with high frequencies Neutral mutations don t affect phenotype Main idea modern variation neutral variation rather than adaptive variation Supported by sequencing data Nucleotide substitutions more likely in 3rd base of codon than 1St or 2nd Change amino acid usually harmful to encoded protein Migration and Nonrandom Mating Gene ow when individuals migrate between populations have different allele freguencies Migration tends to reduce differences between two populations Tends to enhance genetic diversity Nonrandom Mating individuals choose mates irrespective of their genotypes and phenotypes 1 Assortative mating individuals with similar phenotypes more likely to mate homozygotes 2 Disassorative mating dissimilar phenotypes mater heterozygosity Inbreeding choose mater based on genetic history 9 Chapter 25 Origin of Species and Macroevolution Identification of Species Macroevolution evolutionary changes that create new species diversity Species group of organisms maintains distinctive sect of attributes in nature Difficulty in identifying species Subspecies and Ecotypes Amount of separation time for two populations Short likely to be similar and same species Long more likely to show unequivocal differences May find where some differences are apparent but difficult to decide if different species subspecies classification Most common to identify morphological traits ability to interbreed molecular features ecological factors and evolutionary relationships Morphological Traits physical characteristics Drawback 1 Many traits to consider 2 Traits may vary 3 Degree of dissimilarity 4 Members of same species could look very different 5 Members of different species can look very similar Reproductive Isolation prevents one species from successfully interbreeding with other species Four Main Problems 1 Difficult in nature 2 Don t interbreed 3 Not applicable to asexual species 4 Not applicable to extinct species Mechanisms prevent interbreeding between different species Interspecies hybrid two species produce offspring 1 Prezvgotic barriers prevent zygote formation a Habitat isolation geographic barrier prevents contact b Temporal isolation reproduce at different time of dayyear c Behavioral isolation important in mate choice d Mechanical isolation size in genitalia prevents mating e Gametic isolation gametes fail to unite 2 Postzvgotic barriers block development of fertile individuals a Hybrid inviability fertilized egg can t progress past early embryo b Hybrid sterility interspecies hybrid viable but sterile 0 Hybrid breakdown hybrids viable and fertile but subsequent generations have genetic abnormalities Molecular Features compare features to identify similarities and differences 1 DNA sequences within genes 2 Gene order along chromosomes 3 Chromosome structure and number Ecological Factors can be used to distinguish between species Many bacterial species are distinct based on ecological factors Drawback different groups sometimes display very similar growth characteristics Species Concepts Biological species concept species can interbreed with same species but not with other species Evolutionary lineage concept species based on separate evolution of lineages Ecological species concept each species occupies ecological niche unique set of habitat resources that species requires and its in uence on environment Mechanisms of Speciation Speciation formation of new species Cause accumulation of genetic changes Patterns of Speciation Cladogenesis division of species into two or more species requires gene ow between populations to be interrupted Allopatric speciation prevalent method for cladogenesis where some members of species become geographically separated Sympatric speciation members of species within same range diverge into two or more different species Mechanisms 1 Polyploidy two or more sets of chromosomes a Plants more tolerant than animals b Can occur through nondisjunction autoploidy c Alloploids chromosomes from two or more different species Established i Compete unsuccessfully and become extinct ii Coexist with parental species iii Replace parent species 2 Adaption to local environments 3 Sexual selection The offspring can reproduce with itself or similar individual reproductively isolated from each parent wrong chromosomes number Pace of Speciation Gradualism each new species evolves continuously over long spans of time Large phenotype differences Punctuated equilibrium species in equilibrium for long periods and then short rapid bursts of change