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BIOL1001 Text Book Chapter Notes

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BIOL 1001
Tamara Kelly

BIOL 1001 Chapter 3 Notes: Intro to Evolution Biodiversity: reflects the reality that life on earth exists from the ocean floor to well into the atmosphere Ecosystems: group of communities interacting with their shared physical environment Community: populations of all species that occupy the same area Population: Group of individuals of the same kind (that is, the same species) that occupy the same area Multicellular organism: individual consisting of interdependent cells Cell: the smallest unit with the capacity to live and reproduce, independently or as part of a multicellular organism Hierarchy of Life: each level exhibits emergent properties that do not exist at lower levels. Autotrophs: such as plants, synthesize organic carbon molecules using inorganic carbon Heterotrophs: all animals, they obtain carbon from organic molecules, either from living hosts or from organic molecules in the products, waste, or remains of dead organisms. Chemotrophs: obtain energy by oxidizing inorganic or organic substances Phototrophs: obtain energy from light Chemoautotrophs: carbon source: CO2, inorganic molecules, found in some bacteria and archaeans; not in eukaryotes Chemoheterotrophs: carbon source: organic molecules, found in some bacteria and archaeans, and also in proteins, fungi, animals, and plants Photoautotroph: carbon source: CO2, energy source: light, found in some photosynthetic bacteria, in some proteins, and in plants Photoheterotrophs: carbon source: organic molecules, energy source: light, found in some photosynthetic bacteria Selection occurs when some force or phenomenon affects the survival of individual organisms. -when a large population of individuals is exposed to a lethal factor and only resistant individuals survive -inheritance of offspring -key factors behind selection: selective force and the capacity for explosive population growth -major force responsible for evolution and biodiversity -genetic variation Bacteria that are resistant to antibiotics can survive and reproduce, overwhelming the defenses of an individual and institutions. Similar to pests and pesticides. Theory of Evolution -all organisms alive today descend from a common ancestor, which explains why all organisms share certain features (unity). It also tells us that species change over time as a result of natural selection (diversity). -all organisms use ATP as their cellular energy source, have DNA as genetic material, and have plasma membranes composed of lipid bilayers -Central ideas of Darwin’s theory of evolution by natural selection: 1) individual organisms in a population vary in many heritable traits 2) any population has the potential to produce far more offspring than the environment can support 3) struggle for existence, and some individuals have traits giving them an advantage in their community 4) more likely to survive and reproduce surviving organisms pass on favourable traits to their offspring. In this way incidence of traits will change. Chapter 20 Notes: History of Evolutionary Thought/Evidence for Evolution -Natural Theology: dominated biological research, sought to name and catalogue all of God’s creations, i.e. living organisms -Aristotle’s ladder of life: Great Chain of Being: careful study of species, position, and purpose. -Sir Francis Bacon: established the importance of observation, experimentation, and inductive reasoning. -Biogeography, comparative morphology, and geology promoted a growing awareness of change -through documentation and findings of fossils, giving rise to the understanding that the Earth is very old. -Buffon: proposed some animals must have changed since their creation -vestigial structures: useless body parts seen today must have had some function in ancestral organisms -Cuvier: Catastrophism: reasoning that each layer of fossils represented the remains of organisms that had died in a local catastrophe such as a flood. Repeat of this happened, forming a different set of fossils in the next higher layer. -Lamarck: Biological Evolution: -“perfecting principle” caused organisms to become better suited to their environments. -simple organisms evolved to more complex ones moving up ladder of life -Principle of use and disuse: body parts grow in proportion to how much they are used, unused structures grow weaker and shrink -Inheritance of acquired characteristics: changes that an animal acquires during its lifetime are inherited by its offspring. -his proposed mechanisms do not cause evolutionary change -Four main contributions: 1) species change through times 2) changes passed from one generation to another 3) organisms change in response to the environment 4) hypothesized the existences of specific mechanisms that caused evolutionary change -James Hutton proposition that slow and continuous physical processes acting over long periods of time, produced earth’s major geological features. -Gradualism: view that earth changed slowly over time, contrasted to Cuvier’s catastrophism. -Uniformitarianism: unchanging earth, geologic processes proceed very slowly, millions of years for landscape to configure. -Plate tectonics can be responsible for continental drift, and on distribution and evolution of organisms -Charles Darwin: - observed species in Galapagos Islands -animals on different islands varied slightly in form -artificial selection: breeding individuals with favourable characteristics, so traits would be enhanced in future generations Darwin’s Innovations: 1) Physical evidence 2) Evolutionary change occurs in groups of organisms rather than individuals. Some members survive and reproduce more successfully than others. 3) Multistage process, variations arise within groups, natural selection eliminates unsuccessful variations and the next generation inherits successful variations. 4) Some organisms function better in a particular environment -Natural Selection: mechanism that drives all evolutionary change, acted on the variability within groups of organisms, favoured traits are preserved, unfavoured are eliminated. Most fossils found in sedimentary rock, they preserve the details of hard structures (that are not readily decomposed) such as bones, teeth, shells, wood, leaves, and pollen of plants. -Conditions of low oxygen or high acidity are idea for fossilization -Some fossils are casts or moulds; in others, dissolved minerals replace the original materials. -Radiometric dating involves the use of isotopes and sometimes allows actual age to be associated with different rock strata. -isotopes begin to decay from the moment they form. -dating is limited by the half-life of the isotope which is the amount of time it takes half of the initial amount of isotope to decay into more stable elements. -carbon dating – ratio of Carbon 14 and Carbon 12 to determine fossil age -living organisms effected by climate and environmental conditions -plate tectonics: earth’s crust is broken into irregularly shaped plats of rock and float on mantle, currents cause the plates to move, also known as continental drift. -Pangaea: supercontinent present on earth 250 million years ago, continental drift is what separated it into the continents we know today. -movement of continents towards the poled caused formation of glaciers -massive volcanic eruptions, asteroids have also impacted climate and atmosphere. -extinction of many forms of life Continuous and Disjunct Distributions -continuous distribution: many species living in suitable habitats throughout large areas -disjunct distributions: closely related species live in widely separated locations -dispersal and vicariance create disjunct distribution -dispersal: movement of organisms away from their place of origin; disjunct distribution is produced if a new population becomes established on the far side of a geographical barrier. -Vicariance: fragmentation of a continuous geographic distribution by external factors Biotas: result of geographical isolation of continents, means all organisms living in a region. -Wallace’s Biogeographical Realms: Nearctic, Neotropical, Ethiopian, Palearctic, Oriental, and Australian. -Endemic Species: species that occur nowhere else on earth, such as marsupials that are native to Australia. -Monotremes: egg laying mammals -Placentals: e.g. bats, rodents, and dingos. -biotas of Nearctic and palearctic are similar (i.e. North America and Eurasia) -Convergent Evolution: distantly related organisms that are similar in appearance not because of a shared ancestor but because they occupy similar environments. -convergence between placentals and marsupials. Chapter 2: 2.2 -Earth is 4.6 billion years old -solar system was formed by the gravitational condensation of matter present in a molecular cloud, which consisted mostly of hydrogen. -condensation of interstellar gas forms stars -earth bombarded with rock from solar system (meteorites) , and volcanic and seismic activity. -the primordial atmosphere contained an abundance of water vapour, H2S, CO2, NH3, and CH4. -some were formed spontaneously others were formed by volcanic eruptions -Oparin and Haldane proposed that organic molecules essential to the formation of life – including amino acids, sugars, and the nucleotide bases that form DNA and RNA (could have been made in the absence of life – abiotic synthesis). -this hypothesis is that the early atmosphere was a reducing atmosphere because of the presence of large concentration of molecules such as Hydrogen, methane and ammonia -large complex molecules are possible in formulation because the elements above contain max number of electrons and are said to be fully reduced. -today’s atmosphere is an oxidizing atmosphere. The Miller Urey Experiment -lack of oxygen in primordial atmosphere meant there was no Ozone layer to block UV light from the sun -Oparin and Haldane hypothesized that the UV light along with lightning provided the energy that combined the reducing conditions present in the atmosphere, would lead to accumulation of simple “building blocks” required for life. -Miller placed components of a reducing atmosphere – hydrogen, methane, ammonia, and water vapor – in a closed apparatus and exposed the gases to an energy source in the form of continuously sparking electrodes. -Result: large assortment of organic compounds in the water, including Urea, amino acids, lactic, formic and acetic acids. --The Miller-Urey apparatus demonstrating that organic molecules can be synthesized spontaneously under conditions stimulating primordial earth -When HCN and CH2O were added to the apparatus all the building blocks of complex biological molecules were produced – amino acids, fatty acids, the purine and pyrimidine building blocks of nucleic acids, sugars such as glyceraldehyde, ribose, glucose, and fructose; and phospholipids (form lipid bilayers of membranes) -scientific debate if there was enough ammonia and methane in the atmosphere during primitive earth for these things to occur. -however could have quite possibly occur near volcanoes and hydrothermal vents of the ocean floor -organisms near these vents are able to thrive in extreme conditions as well as in the absence of light. -polymerization: process in which monomers are linked together to form polymers -doubtful it could have occurred in aqueous environment of primordial earth. Macromolecules could be easily broken down or hydrolyzed. -alternative hypothesis: solid surfaces especially clays, would have provided unique environment for polymerization to occur. -clay consists of very thin layers of minerals separated by layers of water only a few nanometers thick -layered structure absorbs ions, and organic molecules and promotes their interactions, including condensations and other rxns. -clays can also store potential energy Protobionts -term given to a group of abiotically produced organic molecules that are surrounded by a membrane or membrane-like structure. -allowed for an internal environment to develop differently than the external one -concentration of key molecules could be higher and molecules could attain more order in a closed space -protobionts could have formed spontaneously on primordial earth -e.g. liposomes, which are small membrane bound spheres, can be formed when lipid molecules accumulate in aqueous environment, they ar selectively permeable, they swell and contract depending on the osmotic conditions Chapter 17: Microevolution: Genetic Changes within Populations - Penicillin first antibiotic drug based on naturally occurring substance that kills bacteria such as Staphylococcus aureus. - Realization that some bacteria could survive low doses and that the offspring of those germs would be more resistant to the drug - Streptococcus pneumonia is leading cause of infectious death world-wide - How do bacteria become resistant to antibiotics? - Genomes of bacteria vary among individuals, some bacteria have genetic traits that allow them to withstand attack by antibiotics - Surviving bacteria reproduce and resistant organisms become more common in later generations - Process of selection - Evolution of antibiotic resistance in bacteria is an example of microevolution: heritable change in the genetics of a population - Population: all individuals of a single species that live together in the same place and time. 17.1: Variation in Natural Populations - Phenotypic variation: differences in appearance or function that are passed from generation to generation. 17.1a: evolutionary biologists describe and quantify phenotypic variation - Quantitative variation: individuals differ in small, incremental ways - This data is displayed in a bar graph or if sample is large enough as a curve. Displaying continuous variation among members of a population. - The width of the curve is proportional to the variability – the amount of variation – among individuals, and the mean describes the average value of the character. - Qualitative variation: they exist in two or more discrete states, and intermediate forms are often absent. - Polymorphism: the existence of discrete variants of a character. E.g. human blood groups (A, B, AB, and O) - Phenotypic polymorphisms are expressed quantitatively by calculating percentage or frequency of each trait. 17.1b: Phenotypic Variation Can Have Genetic and Environmental Causes - Phenotypic variation within populations may be caused by genetic differences b/w individuals, by differences in the environmental factors individuals experience, or by an interaction between genetics and the environment - E.g. of environmental effects: soil acidity effects the expression of the gene controlling flower colour in the common garden plant hydrangea macrophylla. Acidic soil produces blue, neutral produces pink. - Some circumstances, organisms with different genotypes exhibit the same phenotype. - Organisms with the same genotype sometimes exhibit different phenotype. - Only genetically based variation is subject to evolutionary change. - Breeding experiments can demonstrate the genetic basis of phenotypic variation. 17.1c: Several Processes Generate Genetic Variation - Genetic Variation: two potential sources: production of new alleles and the rearrangement of existing alleles. - new alleles probably arise from small-scale DNA mutations - rearrangement of existing scales into new combinations can result from larger scale mutations in chromosome structure, genetic recombination, including crossing over b/w homologous pairs in meiosis, independent assortment of non-homologous chromosomes, and random fertilization of genetically different sperm and eggs 17.1d: Populations Often Contain Substantial Genetic Variation - Gel electrophoresis to identify polymorphisms in diverse organisms - Technique separates two or more forms of a given protein if they differ significantly in shape, mas or net electrical charge - Identification of a protein polymorphism by inferring genetic variation at the locus coding for that protein. - Result: much genetic variations 17.2a: All Populations Have a Genetic Structure - Gene Pool: sum of all alleles at all gene loci in all individuals - Genotypic Frequencies: percentages of individuals possessing each genotype - Allele Frequencies: abundances of one allele relative to others at the same gene locus in individuals of a population. - Relative abundances: relative commonness of populations within a community. 17.2b: Hardy Weinberg Principle - Null Models: predict what they would see if a particular factor has no effect, they serve as theoretical reference points against which observations can be evaluated. - Hardy Weinberg Principle: specifies the conditions under which a population of diploid organisms achieves genetic equilibrium, the point at which neither allele frequencies nor genotype frequencies change in succeeding generations - Mathematical model that describes how genotype frequencies are established in sexually reproducing organisms. - Conditions: 1) no mutations occurring. 2) The population is closed to migration from other populations. 3) The population is infinite in size. 4) all genotypes in the population survive and reproduce equally well. 5) Individuals in the population mate randomly with respect to genotypes - If conditions are met, allele frequencies will never change, and genotype frequencies will stop changing after one generation - Therefore, microevolution will not occur 17.3: Agents of Microevolution - Population’s allele frequencies will change overtime if conditions of Hardy Weinberg Principle are not met. - Agents of microevolution: mutation, gene flow, genetic drift, natural selection, and nonrandom mating 17.3a: Mutations create new genetic variations - Mutation: heritable change in DNA, which introduces new genetic variation into population - Deleterious mutations: alter an individual’s structure, function, or behavior in harmful ways - Lethal mutations: cause the death of organisms carrying them, if a lethal allele is dominant, both homozygous and heterozygous carriers suffer effects. If recessive it affects only homozygous recessive individuals. - Neutral mutations: neither harmful nor helpful – amino acid sequence not altered - Advantageous mutation: confers some benefit on an individual that carries it, natural selection might preserve the new allele and even increase its frequency over time. 17.3b: Gene Flow Introduces Novel Genetic Variants into Population - gene flow: The transfer of genes from one population to another through the movement of individuals or their gametes. - dispersal agents e.g. pollen carrying wind or seed carrying animals responsible for gene flow in most plant populations - phenotypic or genetic markers to identify immigrants in a population, to demonstrate they reproduces and contributed to the gene pool of their adopted population - many immigrant females do not foster gene flow because they do not contribute to the gene pool of the population they join. - evolutionary importance of gene flow depends on the degree of genetic differentiation b/w populations and the rate of gene flow b/w them. 17.3c: Genetic Drift Reduces Genetic Variability within Populations - Genetic Drift: random fluctuations in allele frequency as a result of chance events; usually reduces genetic variation in a population - Has especially dramatic effects on small populations, violating Hardy-Weinberg Principle assumption of infinite population size - chance deviations from expected results - which cause genetic drift – occur whenever organisms engage in sexual reproduction, simply because their population sizes are not infinitely large - particularly common in small populations because only a few individuals contribute to the gene pool and b/c any given allele is present in very few individuals - genetic drift leads to the loss of alleles and reduced genetic variability - population bottlenecks and founder effects, foster genetic drift - Population bottlenecks: a stressful factor such as disease, starvation, or drought kills a great many individuals and eliminates some alleles from a population, producing a population bottleneck. -this reduces genetic variation even if the populations numbers later rebound - Founder Effect: when a few individuals colonize a distant locality and start a new population, carry only a small sample of the parent populations genetic variation -by chance some alleles may be missing from the new population while other rare ones might appear more frequently -genetic drift has important implications for conservation ecology -endangered species experience sever population bottlenecks which result in the loss of genetic variability -limited genetic variation, as well as small numbers, threatens populations of endangered species. 17.3d: Natural Selection Shapes Genetic Variability by Favouring Some Traits Over Others - Natural Selection: process by which such traits become more common in subsequent generations. (Violates Hardy Weinberg Principle) - Can change the allele frequencies, it is the phenotype of an individual organism, rather than any particular allele, that is successful or not. - Reproduction causes both favourable and unfavourable traits to be passed on to the next generation. - Relative fitness: number of surviving offspring that an individual produces compared with number left by others in the population. - Directional Selection: when individuals near one end of the phenotypic spectrum have the highest relative fitness - Shifts trait away from mean to a more favoured extreme. - Stabilizing Selection: individuals expressing intermediate phenotypes have the highest relative fitness - Reduces genetic and phenotypic variation and increases the frequency of the intermediate phenotypes - Most common mode of natural selection - Disruptive Selection: when extreme phenotypes have higher relative fitness than intermediate phenotypes - Favours both extreme phenotypes, promoting polymorphism - Much less common 17.3e: Sexual Selection Often Exaggerates Showy Structures in Males - Sexual Selection: has fostered the evolution of showy structures such as brightly coloured feathers, long tails, or impressive antlers – as well as elaborate courtship behavior in the males of many animal species - Intersexual selection: selection based on the interactions b/w males and females - Intrasexual selection: selection based on the interactions b/w members of the same sex. i.e. males use their large body size, antlers, tusks, to intimidate, injure, or to kill rival males. - Sexual selection is the most probable cause of sexual dimorphism, differences in the size or appearance of males and females - Sexual selection pushes phenotypes toward one extreme 17.3f: Nonrandom Mating Can Influence Genotype Frequencies - HW assumption – individuals must select mates randomly with respect to genotypes - Many organisms do however mate non-randomly, selecting a mate with a particular phenotype and underlying genotype - Because individuals with similarly genetic based phenotypes mate with each other, the next generation will contain fewer heterozygotes - Inbreeding: form of nonrandom mating in which individuals that are genetically related mate with each other - Organisms that live in a small/closed populations tend to mate with relatives - Inbreeding increases the frequency of homozygous genotypes and decreases the frequency of heterozygotes. Recessive alleles are often repressed. 17.4a: Diploidy Can Hide Recessive Alleles from the Action of Natural Selection - diploid condition reduces the effectiveness of natural selection in eliminating harmful recessive alleles from a population - such alleles might be disadvantageous in homozygous state, they may have zero or no effect in heterozygous state - recessive alleles can be protected from natural selection by the phenotypic expression of the dominant allele - diploid state preserves recessive alleles at low frequencies, in large populations - in small populations, a combination of natural selection and genetic drift can eliminate harmful recessive alleles - when a recessive allele is common, most copies are present in homozygotes, when the alleles is rare, most copies exist as heterozygotes - rare alleles that are completely recessive are protected from the action of natural selection because they are masked by dominant alleles in heterozygous individuals 17.4b: Natural Selection Can Maintain Balances Polymorphisms - Balanced Polymorphism: one in which two or more phenotypes are maintained in fairly stable proportions over many generations. - Natural selection preserves it when heterozygotes have higher relative fitness, when difference alleles are favoured in different environments, and when the rarity of a phenotype provides an advantage. - Heterozygote Advantage: a balances polymorphism can be maintained, when heterozygotes for a particular locus have higher relative fitness than either homozygote - e.g. maintains of the HbS (sickle) allele , which codes for a defective form of hemoglobin in humans - it is an oxygen transporting molecule in red blood cells - low oxygen causes the red blood cells to take a sickle shape - most common in regions with malarial parasites infect red blood cells in humans 40.10: Mates as Resources - Mating Systems: maximize reproductive success, in response to the amount of parental care that offspring require and other aspects of species’ ecology. - Monogamy: a male or female form a pair bond for a mating season or for the individuals entire reproductive lives. - Polygamy: occurs when one male has active pair bonds with more than one female (polygyny) or one female has active pair bonds with more than one male (polyandry) - Promiscuity: occurs when males and females have no pair bonds beyond the time it takes to mate 40.11: Sexual Selections - Sexual dimorphism in which one gender is larger or more colourful than another can be an outcome of sexual selection - Adornments or weapons can attract other females, and ward off other males - A males large size, large horn, bright feathers, might indicate that the male is healthy, harvest resources efficiently, or simply manage to survive to an advanced age - His features signify his quality/genetic makeup that he can potentially fertilize a females eggs with successful alleles - Can potentially gain access to large territories and resources - Males locate cluster of females and fight to keep others away, those who can inseminate the most females means they will increase their offspring’s chances of living long enough to reproduce - In some populations, females have a more active mate choice…they inspect potential male partners - Lek: a display ground where males each possess a small territory from which they court attentive females - E.g. a peahens mate choice influences her offspring’ chances of survival – peacocks with more attractive tails tend to survive and mate with more female 19.1a Fake Flowers - The fungus, Puccinia monoica, affects the growth of leaves, changing their appearance and odour making it flower-like and appear to produce nectar 19.1b Carnivorous Plants - Plants use different methods to trap insects for nitrogen - Not all carnivorous plants share a common ancestor 19.1c Mammals with Flat Tails Are Not Always Beavers - Fossil found of: Castorcauda lutrasimilis mammal that had modified tail vertebrae fattened like living beavers – but beavers are not the only mammals with flat tails - Flowerlike structures are not always flowers, carnivorous plants are not necessarily closely related, and looking a mammals tail may give you a different picture of its relationship than its skull - Although the tails of aquatic mammals with flattened tails are broad and flat with similarities in caudal vertebrae, the skills and teeth are different 19.2 Systematic Biology: Overview - Systematic biology, classification, and taxonomy help us organize and understand info about the biological world - Two majors goals of Systematics: 1) reconstruct the phylogeny or evolutionary history of a group of organisms. - Phylogenies are represented in phylogenetic trees, which are formal hypotheses identifying likely relationships among species - Accurate phylogenetic trees are used to compare and analyze the evolutionary processes - It allows us to distinguish similarities from a common ancestor from those that evolved independently in response to similar environments - 2) Taxonomy: identification and naming of species their placement in a classification - Classification: an arrangement of organisms into hierarchical groups that reflect their relatedness 19.3 The Linnaean System of Classification - Linnaeus described and named thousands of species on the basis of their similarities and differences - Taxonomic hierarchy: arranging organisms into categories based on family (group of genera that closely resemble one another), Orders, Classes, Phyla, and into Kingdoms. - Lastly all life on earth is classified into three domains and organisms included into any category of the taxonomic hierarchy compromise a taxon 19.5. Evaluating systematic Characters - Systematists seek characters that are independent markers of underlying genetic similarity and differentiation - Stugy traits in which phenotypic variation reflects genetic differences – try to exclude differences caused by environmental conditions - Must be genetically independent, reflecting different parts of organisms’ genomes - Systematic analyses rely on the comparison of homologous characters as indicators of common ancestry and genetic relatedness - Analogous characters are homoplasious (homoplasies), phenotypic similarities that evolved independent in different lineages - Homoplasies: characteristics shared by a set of species often because they live in similar environments but not present in their common ancestor, often the product of convergent evolution - Systematists exclude homoplasies from their analysies because they provide no information about shared (genetic) ancestry - Homologous bones, different structures and functions - Homologous characters emerge from comparable embryonic structures and grow in similar ways during development - Mosaic evolution: refers to the reality that in all evolutionary lineages, some characteristics evolve slowly, whereas others evolve rapidly - Ancestral characters: old forms of traits, and derived characters (new form of traits) are displayed in species as a mixture - Presence of a vertebral column is a derived character because fossils of the earliest animals lack backbones 19.6 Phylogenetic Inference and Classification - phylogenetic trees portray the evolutionary diversification as a hierarchy that reflects branching pattern of evolution - each branch represents the descendants of a single ancestral species - monophyletic taxa: those derived from a single ancestral species - polyphyletic taxa: species from separate evolutionary lineages - paraphyletic taxa: ancestor and some, but not all, of its descendants - assumption of parsimony: that the simplest explanation should be most accurate - unlikely same changes evolved twice in one lineage 19.6a/b - traditional evolutionary systematics: groups together species that share ancestral and derived characters - Cladistics produces phylogenetic hypotheses and classifications that reflect only the branching pattern of evolution. It ignores morphological divergence - Cladists group together species that share derived characters - Clade: a monophyletic group of organisms that share homologous features derived from a common ancestor - Cladograms are phylogenetic trees illustrating a hypothetical ancestor at each branching point - Always display monophyletic groups and use principle of parsimony - Phylocode: identifies and names clades instead of placing organisms into the familiar taxonomic groups 19.7: molecular data - most systematists use molecular characters as part of the data set when conducting phylogenetic analyses - molecular data include nucleotide base sequences of DNA and RNA or the amino acid sequences of the proteins for which they code - because DNA is inherited it provides clues to the evolutionary relationships of organisms - Advantages: 1) provide abundant data because every amino acid in a protein and every base in a nucleic acid can serve as a separate character for analysis - 2) molecular sequences can be compares between distantly related organisms that share no organismal characteristics – as well as study closely related species with morphological differences - 3) many proteins and nucleic acids are not directly affected by the developmental or environmental factors that cause non-genetic morphological variation - Disadvantage: since there are only 4 nucleotide bases at each position in DNA or RNA sequence and only 20 possible amino acids. If two species have the same base substitution, their similarity may have evolved independently – therefore making it difficult to verify if they evolved from a single common ancestor 19.7a - Molecular clock: a technique for dating the time of divergence of two species or lineages, based on the number of molecular sequence differences between them. - Mosaic evolution occurs at a molecular level, so different molecules exhibit individual rates of change - Mitochondrial DNA evolves relatively quickly, useful for dating evolutionary divergences that occurred within the last few million years - Chloroplast DNA and genes that encode ribosomal DNA evolve much more slowly, providing info for divergences that are hundreds of millions of years old 19.7b - Species that diverged recently from a common ancestor should share many similarities in their molecular sequences, whereas more distantly related species should exhibit few similarities - Amino acid sequencing allows systematists to compare the primary structure of protein molecules directly - When two species exhibit similar amino acid sequences for the same protein, systematists, infer their genetically similar and evolutionary related 19.7c - insertion or deletion of base pairs can change the length of a DNA sequence and the relative locations of the specific positions along its length - therefore, systematists align the sequences they are comparing to ensure that the nucleotide base being compared are at the exact same position - by determining where insertions or deletions have occurred, systematists match up the positions of the nucleotides 18.1: What’s in a Name? - communication can affect both inter- and intra- specific behavior - biologists use scientific names (Latinized descriptions) of the organism bearing the name, for precise communication 18.2 Definition of Species - Species are the fundamental taxonomic units of biological classification. Environmental laws are framed in terms of species. - 1)Biological Species Concept defines species as a group of organisms that can successfully interbreed and produce fertile offspring - 2)The Phylogenetic Species Concept defines a species as a group of organisms bound by a unique ancestry - 3)The Ecological Species Concept defines a species as a group of organisms that share a distinct ecological niche - Problems with the definitions: 1) it deals only with species that reproduce sexually, and ignores ones that reproduce asexually. Reproduction patterns can blur the definition of species - Androdioecous organisms exist as natural populations of functional males and hermaphrodites but include no true females - Gynogenetic species have only females – use internal fertilization, by which they seduce males for their sperm to stimulate the eggs and achieve reproduction - These two examples do not fall under the biological species concept does this mean they are not species? - 2)The definition also does not apply where there is hybridization (when two species interbreed and produce fertile offspring). - Hybridization b/w species that produces sterile offspring does not put them outside the definition - Sterile hybrids result when horses are crossed with zebras and lions with tigers. Mules are the sterile hybrids of donkeys and a female horse, where as hinnies are sterile hybrids of a male horse and a female donkey - Asexually reproducing populations had a higher frequency of mutations in mitochondrial protein-coding genes than sexually repr
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