Lectures 8 and 9
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Date Created: 02/27/15
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 by geographic barriers Doesn t always happen but if they become differentiated mutation drift selection 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 Parapatric Speciation occurs on a larger scale large numbers of a population gradually becoming differentiated genetic drift and selection along the range of the population It s a gradation of speciation adjacent demes can interbreed but the one on either end cant Create Ring species gradual change in the species along the ring Ring species shows how microevolutionary events can lead to macroevolution Sympatric Speciation speciation occurs without physical separation within the range of the ancestral population Happens more in plants normally due to a sudden genetic event that causes rapid reproductive isolation Autopolyploidy or allopolyploidy Hybrids offspring of genetically dissimilar parents Can be between species or within a species Hybrid zone the area of contact when 2 species come back together because some limited mating is taking place Introgression the introduction of alleles from one species gene pool into that of another closely related species due to limited hybridization Mule deers stot white tailed deer gallop The hybrids stollop that isn t effective at escaping predators Hybrid speciation happens in plants but now getting evidence of it happening in animals if its phenotypically equipped to survive in the habitat where it occurs receives genomes that enables it to breed successfully with other such hybrids but not breed with either parent species doesn t have to compete with other parental species for resources by either escaping to a new habitat or its new phenotype causes it to utilize different resources from those used by the parent species Hybridization of 2 fruit ies parents 1 feeds on X parent 2 feeds on y hybrid feeds on 2 Pace of Evolution Evolution of modern horse required link Darwin evolution is very slow Or punctuated equilibrium Phyletic gradualism Darwin thought species evolved in a stepwise manner very slowly over generations over time Punctuated equilibrium Eldrege and Gould major changes that occur relatively suddenly and punctuate long period of stasis Assortative mating Individuals genetically predisposed to be better adapted for intertidal life would likely hang together This might mean they would also be more likely to mate with each other This would generate a smaller e ective population where inbreeding could magnify aquatic adaptations relatively quickly The Genetics of Evolution Motoo Kimura most mutations are neutral and aren t subject to natural selection and that most genetic variation across genomes was neutral due to genetic drift DNA should mutate at a relatively constant rate neutral mutations should become fixed in populations at constant rates the time it took for new mutations to arise and then spread randomly through populations Via genetic drift Silent synonymous mutation doesn t change the amino acid sequence encoded by a particular gene might not be neutral Neutral mutations can be any mutation that either has no phenotypic effect of has no effect on the Darwinian fitness of the individual carrying it Neither adaptive nor deleterious EX Mitochondrial mutations can count up the difference in species for certain mutations you can compare how long ago the 2 compared species had split from a common ancestor Pseudogenes ve Protein coding genes Proteome the entire complement of the proteins that is or can be expressed by a call tissue or organisms genes that code for a finished product RNA tRNA ribosomal RNA non coding functional DNA ends of chromosomes Pseudognes non coding parts Genes that no longer appear to have any function predict more mutations in pseudogenes then proteome genes Molecular Clock use it to determine the amount of time it took to change because pieces of DNA at a set rate Neutral evolution is different in different organismal lineages Different genes evolve at different rates The rate of neutral evolution can speed up or slow down over time We are the results of ancient selections we can compare the ratio of nonsilent to silent mutations in a particular gene they can determine whether that gene has been under selective pressure Purifying selection purified the gene by removing any deleterious variations If a gene underwent purifying selection the ratio of nonsilent to silent mutations should be zero Positive selection genes products is less rigid and mutations can be tolerated resulting in a new alleles of that productprotein In gene changing due to natural selection NSS gt 1 FOXPZ expressed in brain and spinal chord for the plasticity of nervous system wiring Humans with mutant versions have severe language and speech disabilities cant understand grammar or language construction In humans 2 nonsilent that have occurred somewhere in the past 6 million years This mutation must have been very adaptive because if it were bad that organism would die Gene duplication and Gene recruitment Step 1 You can add genetic information to the genome Mistake can happen during DNA replications or during crossing over at meiosis due to unequal crossing over Base pair substitutions duplications deletions All of these cane be harmful good or neutral Pseudogenes can wake back up after some mutation Gene duplication 1 One gene evolve new regulation and function 2 One gene mutates into a pseudogene with no function 3 Each gene will evolve to specialize in one of the functions of the original gene but a little different Can provide the raw material for new genetic functions Gene recruitment the enlistment of a changedmutated version of a gene for a function that s different or somewhat different from the original function Ecoli unlike the wild type this Ecoli could feed on Citrate a buffer No longer even needed glucose PCPpentachlorophenol feeding Shpingobium natural mutations sphingobium is a type of bacteria that developed tools to break down PCP in the soil It uses an enzyme that strip off the chloride ions and break apart the ring for energy Irreducibly complex couldn t be made in nature had to be designed Michael Behe and William Paley The complexity of living structures could mean only that they had to be intelligently designed Snake venom slowly developed venom Know known that the gene coding for it is Crotamine and it is very closely related to genes coding for defensins small proteins found in animals that provide antibacterial protection and found in immune system cells Snake venoms are more related to other snakes than others Still differentiated green mambas hunting in trees are more effective against snakes and birds black mambas hunt in trees more effective against rodents Poisons need to be ingested and venom needs delivery mechanisms into blood The Eye all vertebrates have lightsensitive photoreceptor cells called rods andor cones comprising the outermost layer of retina Rods night vision 0 Have rhodopsin 0 Confer high sensitivity to light 0 Provide low resolution Cones color and day vision 0 Contain different pigments 0 Low sensitivity to light Provide a high resolution 0 Confer color vision if more than on type of cone is present Humans have 3 specific sensitive cones Insects have different photoreceptors that are sensitive to uv Can t see red Birds and reptiles have at least 4 types of cones with less overlaps so they have better Light sensing opsins are apart of protein family called th GProtein Coupled receptors called serpentine proteins because they snake in They are involved in sensing external stimuli Earliest ancestors a GPCR mutated to be able to see different type of stimulus light Eventually developed into opsin they differentiated in animals to different types of opsins Opsins originally sensed chemicals Eyes probably developed from simple patches of lightsensing cells on the skin towards the head Crystallins transparent stable and evolved from ancestral genes that coded for heat shock proteins chaperone protein The lens itself has heatshock protein properties In the eye it helps focusing light and preventing proteins from clumping Changing gene expression can change the phenotype DNADRNADproteins Transcription factors is a protein that binds to a specific DNA sequence and controls how that sequence of DNA is read Promoter facilitates gene transcription when bound to a transcription factor Enhancer enhances transcription level when bound to a transcription factor like protein Repressor represses transcription level when bound to a transcription factor Mutates increase production of a gene product decrease or shut it off Early development As a zygote develops and undergoes its cleavages the DNA in each cell is repackaged and modified Some genes turn on off some genes code for proteins to shut off and on can be positive or negative Genetic Toolkit the set of genes that determine its body axes morphology segmentations limbs and other features The box genes of mammals and fruit flies are homologous Protostomes and deuterostomes are reversed in body position Protostomes Nervous system is ventral Intestine is dorsal and circulatory system is dorsal Deuterostomes Nervous system is dorsal intestine and circulatory system is ventral Changing gene activity can change phenotype Bird beaks low levels of BMP4 promotes long narrow beaks High level of BMP4 promotes a wide deep beak Calmodulin gene controls the length of the beak Placodes disks of skin cells in embryos Different expression of genes in placodes give rise to different types of scales and feathers Convergent Evolution evolution of 2 unrelated lineages towards a similar form Lecture 9 History of Life on Earth Biodiversity the diversity of living things on earth constantly changing Origin of life not really sure how 4 major phases Generation of small organic molecules from abiotic precursors The joining of these small subunits into macro proteins nucleic acids carbohydrates lipids The packaging of these macromolecules into protocells consisting of a membrane and an intenal space filled with uid that was different from the surrounding medium Origin of selfreplicating molecules that made inheritance possible Abiogensis Aleksandr Oparin first to suggest that chemical reactions in the primitive oceans hat could have created life Properties of life Organized structure Chemical reactions coordinated to perform vital functions Ability to maintain constant internal environment Reaction to stimuli Growth and development Ability to respond to environment changes Ability to reproduce
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