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Differences in Homologous & Analogous Structures: Role in Evolution - Prof. Christopher Gr, Study notes of Biology

The concepts of homologous and analogous structures in biology, their differences, and their significance in evolution. The concepts of common ancestry, variation in populations, natural selection, genetic drift, gene flow, and reproductive isolation. It also discusses the role of mutations, sexual recombination, and the hardy-weinberg equation in evolution.

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2013/2014

Uploaded on 02/17/2014

kirstyn-crosby
kirstyn-crosby 🇺🇸

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Download Differences in Homologous & Analogous Structures: Role in Evolution - Prof. Christopher Gr and more Study notes Biology in PDF only on Docsity! Chapter 22: Descent With Modification: A Darwinian View of Life Evolution: 1. Change over time of the genetic composition of a population (also common ancestry) 2. Decent of modern organisms with modification from preexisting organisms Evolutionary Adaptation: 1. Accumulation of inherited characteristics that enhance organisms' ability to survive in specific environments Pre-Darwinian Theory of Evolution: -Lamarck 1.use and disuse -bodies of living organisms are modified through the use and disuse of parts 2.Inheritance of acquired characteristics -these modifications are inherited by offspring -these ideas are wrong!! Evolution by Natural Selection -Darwin and Wallace developed the theory independently 1. Darwin-voyage of he Beagle 5 year map voyage around the world which resulted in a change in the way we think about biology 2. Wallace-naturalist in Indonesia sent his ideas to Darwin who sent all the ideas to London, changing the way we think about the natural world -individuals do not evolve Natural Selection -a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than other individuals because of those traits -can increase the match between an organism and its environment over time 1. the unequal survival and reproduction of organisms due to environmental forces, resulting in the preservation of favorable adaptations 2. process "select" from what is available in the gene pool 3. new characteristics are not created on demand (natural selection can only act on what is already there) -heritability, reproduction, survival -rapid process -favors individuals that reproduce more than others Mechanism Behind Natural Selection Chart on Page 458 -adaptation is a trait that increases an individuals ability to survive in a particular environment -heritability is the ability of a trait to be passed on to offspring Think about the 100-m dash track and field competition. How can we change this race to reflect the process of natural selection? make them race for food-survival! winners reproduce and the losers don't. Artificial Selection -selective breeding of organisms to encourage the occurrence of desirable traits -analogous to natural selection -a cow that produces a large quantity of milk is an organism that could be produced by artificial selection -humans choose which individuals will reproduce -a farmer should breed a large hen and a large rooster to produce a large chicken 22.3 Evolution is supported by an overwhelming amount of scientific evidence Examples of Natural Selection -soapberry bug -beaks correlate with deepness of the seeds. the bugs with longer beaks survived -figure 22.13 Within a few weeks of treatment with the drug 3TC, a patients HIV population consists almost entirely of 3TC resistant viruses. How can this best be explained? -A few drug resistant viruses were present at the start of treatment, and natural selection increased their frequency. Homologous and Analogous Structures Homologous -structures or other attributes in different species that resemble each other because of common ancestry -Ex: two species have similar traits because their common ancestor had that trait -human, cat, whale, and bat •must have variation Mutations • changes in the nucleotide sequence of DNA • ultimate source of new alleles and genes • no variation in genes without mutations • point mutation: change in one nucleotide base in a gene (also called substitution • small Scale • chromosomal mutations: delete, disrupt, or rearrange many loci on a chromosome • large scale • gene duplications: duplication of whole segments of chromosome •mutation rate averages 1 in every 100,000 genes per generation Sexual Recombination • in sexually reproducing organisms, sexual recombination produces most of the variability in each generation • crossing over during prophase 1 • independent assortment during metaphase 1 Variation With A Population • discrete characters: classified on an either-or basis • flower color in pea plants (purple or white) • quantitative characters: vary along a continuum within a population • determined by multiple alleles for a gene • height, weight Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving Populations • a group of individuals of the same species living in a certain defined area • they are capable of interbreeding Hardy Weinberg Equilibrium • if no evolutionary forces act on a population, its allele frequencies will remain the same from generation to generation • H-W equilibrium: describes a population that is not evolving (allele/gene frequencies don't change from one population to the next) • want to know about a population that doesn't change gene frequencies because it gives us a basis to compare to natural populations • Five assumptions behind H-W equilibrium • no mutations • new alleles are not introduced to the gene pool •mutation could create a new allele that is neither allele 1 or allele 2 • no selection • all of the members of the parental generation survive and contribute equal numbers of gametes to the gene pool • no gene flow • no migration into or out of the population • no genetic drift • the population is sufficiently large that no random changes occur simply due to sampling error when combining alleles to make the next generation. small populations are more prone to random changes than are large populations • random mating • nonrandom mating reduces the level or heterozygous individuals in the next generation • if you don't meet all of these assumptions then something must be changing • no selection at the gene in question, no genetic drift, no gene flow, no mutation, random mating -basic components of the Hardy-Weinberg model include the frequencies of two alleles in a gene pool before and after many random matings -we can use the Hardy-Weinberg principle to predict the proportions of genotypes and alleles in the 2nd generation -this principle is a null hypothesis -mutation is an evolutionary force that could create new genetic information in a population -selection is the only evolutionary force that consistently results in adaptation. mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or natural effects on populations Allele and Genotype Frequencies • allele frequencies • p=frequency of allele 1; q=frequency of allele 2 • p + q =1 • genotype frequencies • p^2= frequency of homozygous dominant • q^2= frequency of homozygous recessive • 2pq=frequency of heterozygous • p^2 + 2pq + q^2 = 1 (H-W equation) • side note from quiz 2- the homozygous dominant alleles are represented by p^2=(0.0)^2=.64 to get the number of peas in a population of 25, multiply 25 by .64 which equals 16 peas. the rest of the yellow peas are heterozygous H-W Equilibrium • figure 23.7 Population Genetics and Human Health • H-W equation can be used to estimate percent of the human population carrying the allele for an inherited disease • PKU is a recessive genetic disorder • frequency of homozygotes with this disorder is q^2 = .0001 • what is the frequency of the dominant and recessive alleles? • p= 99% • q= 1% • figure this out by taking the square root of q which is .01, p+q=1, so p must be equal to .99 • what is the frequency of carriers who do not have PKU? • .0198 • figure this out by 2pq, we had p and q so multiply then together and then multiply by 2 • if a population has the following genotype frequencies (AA=.42; Aa=.46, aa=.12) what are the allele frequencies? • AA=p^2 • aa= q^2 • take the square root of each and there is your answer, or take the square root of p, then p+q=1, .65 +q=1, q=.35 • drives the average of the population in one direction • long necks make it easier for giraffes to reach leaves on trees while also making them better fighters in neck wrestling contests. in both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today? • Disruptive Selection-increase in frequencies of individuals at both extremes • black-bellied seedcrackers have either small beaks (better for eating soft seeds) or long beaks (better for eating hard seeds). there are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers? • causes both extreme phenotypes to be favored over the intermediate phenotypes • tends to increase genetic variation • eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population • Stabilizing selection-decreases the phenotypes that we observe, the average individuals increase frequencies and the frequencies at the extremes will decrease • women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. which kind of selection is most likely at work regarding the birth weight of babies? • causes no change in the average of the population; extreme phenotypes become less common • small lizards have difficulty defending territories, but large lizards are more likely to be preyed on by owls. Which kind of selection acts on the adult body size of these lizards? A population of seed-cracker finches has small and large billed birds specializing in soft and hard seeds, respectively. If climatic change resulted in a loss of the soft-seeded plants, what type of selection would then operate of the finch population? • Directional Selection Sexual Selection • Type of selection that favors a trait giving an individual a competitive edge in attracting or keeping a mate • Can result in sexual dimorphism •male rams have large horns, but female rams don't. •male peacocks have large feathers that he must use resources to get, females do not • Intrasexual selection: direct competition among individuals of one sex for mates of the opposite sex • Intersexual Selection: individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex • females have a choice over who she mates with The Preservation of Genetic Variation • 2 ways to maintain variability: • Diploidy: Maintains genetic variation in the form of hidden recessive alleles • Balancing Selection: occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population • heterozygous advantage • frequency dependent selection- frequency of a particular allele determines whether or not is is favorable. one allele increases in frequency and becomes more and more at a disadvantage. over time there is an equilibrium at a relatively high level in the population Heterozygote Advantage • some individuals who are heterozygous at a particular locus have a greater fitness than homozygotes • sickle cell allele: causes mutations in hemoglobin, but also confers malaria resistance • heterozygous individuals have some resistance to malaria and don't express sickle cell traits • Figure 23.17 Which statement describes the swallow with the greatest evolutionary fitness? • A swallow that lives to be two years old and has four offspring, all of which survive to reproduce themselves Does the ability of a virus cell to infect a new host depend on its drug resistant phenotype? • No, drug-susceptible cells and drug-resistant cells are equally likely to infect a new host • a cells drug susceptibility or resistance does not affect its ability to infect another host although a cells drug resistance would increase that cells chances to spread in an environment containing antibiotics due to increased survival Which of the following statements describes the evolution by natural selection of a Mycobacterium tuberculosis bacteria in their new environment? • the drug-resistance trait is an adaptation to the environment in which human hosts are medicated with the antibiotic rifampin • bacterial cells have higher fitness when they are drug resistant in the new environment in which people have been medicated with antibiotics It would be difficult to assess whether the drug-susceptible or drug-resistant phenotype in a population of Mycobacterium tuberculosis was more fit in an environment without antibiotics • true • in an environment without antibiotics, individual cells probably would not differ in their reproductive rates or their survival. without the application of the drug (antibiotic), it would be very difficult to analyze any differences-one wouldn't even be able to sort the cells Chapter 24: The Origin of Species Concept 24.1: The biological species concept emphasizes reproductive isolation • species: Latin for "kind" or "appearance" • we used to determine species by what an organism looked like The Biological Species Concept • defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring • cannot be applied to: • asexual organisms • fossils • organisms about which little is known regarding their reproduction Limitations of the BSC • figure 24.4 Sympatric "Same Country" Speciation • speciation that takes place in geographically overlapping populations Polyploidy • presence of extra sets of chromosomes in cells due to accidents during meiosis • has caused sympatric speciation in many plant species • describing organisms that have additional sets of chromosomes that have risen during mistakes in meiosis • common occurrence in plants • Autopolyploidy: individual has more than two chromosomes sets, all derived from a single species •missing notes here • Allopolyploidy: species with multiple sets of chromosomes derived from different species • 2 species mate and due to mistakes during meiosis, all chromosomes get transferred to the offspring bringing about a new species because it has a different chromosome number • figure on page 495 One Mechanism for Allopolyploidy • figure 24.11 Plant species A has a diploid number of 12. Plant species B has a diploid of 16. A new species C, arises as an allopolypploidy from A and B. The likely diploid number for species C would be ______? • 28, add the chromosomes together -allopolyploidy has two parent species, there is hybridization, add the chromosome number -autopolyploidy has 1 parents species, double the chromosome number -sympatric speciation has resulted from nonrandom mating due to sexual selection in cichlid fish (figure 24.12) Which of the following is the first step in the process of allopatric speciation? • geographic isolation All but which of the following are likely to promote sympatric speciation? • gene flow-keeps things genetically similar so you wont have speciation • ecological isolation • temporal isolation • polyploidy Concept 24.3: Hybrid Zones Provide Opportunities to Study Factors that Cause Reproductive Isolation -Speciation is dependent upon reproductive isolation(barrier to gene flow) and genetic divergence -since there is gene flow, populations are genetically similar. there is a barrier to gene flow between isolated populations which causes genetic divergence. if enough genetic divergence occurs and the populations come in contact again they become genetically different and interbreeding cannot occur Possible Outcomes for Hybrids • figure 24.14 • barrier breaks down and we have reproduction between 2 species • if there is enough genetic divergence, and the species come back in contact at some point but they die out we have reinforcement • fusion- barrier breaks down but there isn't much genetic divergence,. when populations come back into contact the hybrids aren't at a fitness disadvantage and they are able to interbreed with the other 2 species. over time they fuse back together into a single species • stability-form hybrids but hybrids aren't as fit as the parent species but they can still survive along with the 2 separate species Examples of Stability in Hybrids • eastern europe, toad species • not very much gene flow from one side of the hybrid zone to the other • figure 24.13 The breakdown of Reproductive Barriers: Fusion • figure 24.16 Chapter 25: The History of Life on Earth Early Earth • earth is about 4.6 billion years old • radiometric dating of meteorites and moon rocks • life arose about 3.8 billion years ago • chemical traces in rocks 3.8 billion years ago • fossil bacteria in rocks 3.8 billion years ago • no spontaneous generation now, but must have happened then Conditions on Early Earth • atmosphere • CO2: CH4, NH3, H2S, H2O • no free oxygen • abundant energy to drive reactions • frequent storms wit much lightening • frequent volcanic eruptions • frequent meteor impacts • UV light from the sun • we have oxygen now to form the ozone layer and shield the earth Testable hypotheses explaining the origin of life • 1) abiotic synthesis of small organic molecules • 2) joining these molecules into polymers • 3) packaging these molecules into "protobionts" • 4) the origin of self replicating Miller and Urey Experiments • figure 4.2 • has to do with 1st hypothesis Alternative Hypotheses • 1) first organic compounds may have been synthesized near hydrothermal vents • 2) extraterrestrial origin What were the earliest organisms like? • first organisms were prokaryotes • left behind fossils • bacteria and archaea • fed on accumulated organic molecules (heterotrophic) some were likely autotrophic • many were anaerobic because there was no oxygen • used light and carbon dioxide to produce their own organic material • stromatolites?? • fossilized stromatolites-?? • oxygenic photosynthetic bacteria evolved between 3.5 and 2.7 billion years ago • CO2 + H2O makes food and O2 • oxygen begins accumulating in the atmosphere 2.7 billion years ago Why do some scientists believe that RNA, rather than DNA, was the first genetic material? • RNA has both information storage and catalytic properties The First Eukaryotes • oldest fossils of eukaryotic cells are 2.1 billion years old • Endosymbiotic Theory • mitochondria and plastids were formerly small prokaryotes living within larger host cells • were possibly undigested prey or internal parasites or mutalists • some have chloroplasts and are photosynthetic • figure 25.9 Endosymbiosis and Eukaryotes • extremely important in formation of eukaryotes • uptake of green algae-secondary plastids • uptake of red algae-secondary plastids • uptake of cyanobacterium- primary plastids • uptake of alpha proteoacterium- mitochondria Clock Analogy • shows time scales involved in the history of life on Earth • figure 26.10 Which is the correct sequence of events? • anaerobic cells> photosynthesis> oxygen> aerobic metabolism What evidence suggests that eukaryotic cells formed symbiotic relationships with bacteria? • both chloroplasts and mitochondria contain DNA that is distinct from that found in the nucleus of the eukaryotic cell • similarities in inner membrane structure and functions • both chloroplasts and mitochondria have their own ribosomes and make proteins independent from the cell