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Final Exam Textbook Notes - BIOL 1001

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York University
BIOL 1001
Tamara Kelly

Chapter 3: Selection, Biodiversity, and Biosphere Biodiversity • How organisms obtain carbon: o Autotrophs synthesize organic carbon molecules using inorganic carbon o Heterotrophs obtain carbon from organic molecules, either from living hosts of from organic molecules in the products, wastes, or remains of dead organisms • How organisms obtain energy: o Chemotrophs obtain energy by oxidizing inorganic or organic substances o Phototrophs obtain energy from light Selection • Occurs when some force or phenomenon affects the survival of individual organisms • Occurs when a large population of individuals is exposed to a lethal factor and only resistant individuals survive to reproduce • Key factors are a selective force (pressure) and the capacity for explosive population growth • Major force responsible for evolution and biodiversity Land: Organisms Conquer a New Frontier • Challenges of moving onto land include support, conservation of water, reproduction, and disposal of wastes • Differences between water and air include density and viscosity, which, in turn, affect rates of diffusion and availability of oxygen • Terrestrial animals had skeletons for support and anchoring muscles (allowing locomotion), organs for gaseous exchange, systems for circulating materials within the body, had waterproof coverings to minimize the chances of desiccation, and used nontoxic excretory products (urea and uric acid), whereas aquatic ones still relied heavily on ammonia The Biosphere • Abiotic factors (non-living) include sunlight, temperature, humidity, wind speed, cloud cover, and rainfall. These factors contribute to a region’s climate, the weather conditions prevailing over an extended period of time 1 Solar Radiation: Energy from the Sun • The global pattern of environmental diversity results from latitudinal variation in incoming solar radiation, Earth’s rotation on its axis, and its orbit around the sun • Earth’s spherical shape causes intensity of incoming solar radiation to vary from equator to poles Seasonality: Weather Through The Year 0 • The Earth’s tilt of 23.5 from the perpendicular to the plane on which it orbits the sun produces seasonal variation in the duration and intensity of incoming solar radiation Biotic Factors • For example, competition among organisms, parasitism (a symbiotic relationship in which one organisms benefits at the expense of another), or mutualism, in which both organisms benefit Trophic Interactions: Movements of Energy, Biomass, and Numbers • Producers (photoautotrophs) are organisms that use photosynthesis to capture and harness the sun’s energy and produce most of their own nutritional needs but serve as food for heterotrophs (primary consumers) • Decomposers break down dead organisms and thus make the nutrients available to themselves and other organisms • Photosynthesis is not only a process in plants, but also found rarely in animals when they capture chloroplasts through phagocytosis and use them to capture solar energy but how they control the operations of the chloroplast remains unanswered • Achlorophyllous are plants that cannot photosynthesize, so they obtain energy and nutrients from fungi associated with the roots of neighboring green plants. They still contain trace amounts of chlorophyll a but only one has both chlorophyll a and b Chapter 17: Microevolution: Genetic Changes within Populations Evolutionary Biologists Describe and Quantify Phenotypic Variation • Quantitative variation is when individuals differ in incremental ways (i.e. hair length, height, etc.) • Qualitative variation is when they exist in two or more discrete states, and intermediate forms are often absent (i.e. geese are blue or white feathers) 2 • Existence of discrete variants of a character is called a polymorphism • We describe phenotypic polymorphism quantitatively by calculating the percentage or frequency of each trait Phenotypic Variation Can Have Genetic and Environmental Causes • Under some circumstances, organisms with different genotypes exhibit the same phenotype, and vice versa • Knowing which is responsible is important because only genetically based variation is subject to evolutionary change • Because environmental factors can influence the expression of genes, an organism’s phenotype is frequently the product of an interaction between its genotype and its environment Several Processes Generate Genetic Variation • Two potential sources are the production of new alleles and the rearrangement of existing alleles • Rearrangement can result from larger scale changes in chromosome structure or number and from several forms of genetic recombination Populations Often Contain Substantial Genetic Variation • Identification of a protein polymorphism allows researchers to infer genetic variation at the locus coding for that protein • Gel electrophoresis underestimates genetic variation because it doesn’t detect different amino acid substitutions if the proteins for which they code migrate at the same rate • Every locus exhibits some variability in its nucleotide sequence All Populations Have a Genetic Structure • The sum of all alleles at al gene loci in all individuals is called the population’s gene pool • To describe the structure, first identify genotypes in a sample and calculate genotype frequencies, the percentage of individuals possessing each genotype • Then calculate allele frequency, the relative abundances of the different alleles The Hardy-Weinberg Principle Is a Null Model That Defines How 3 Evolution Doesn’t Occur • 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 • Dominant alleles don’t need to replace recessive ones, and shuffling genes in sexual reproduction doesn’t in itself cause the gene pool to change • Mathematical model that describes how genotype frequencies are established in sexually reproducing organisms • Conditions: o No mutations are occurring o The population is closed to migration form other populations o The population is infinite in size o All genotypes in the population survive and reproduce equally well o Individuals in the population mate randomly with respect to genotypes • Serves as a reference point for evaluating the circumstances under which evolution may occur • Determining which of the model’s conditions are not met is the first step in understanding how and why the gene pool is changing The Agents of Microevolution • Mutations create new genetic variations o Heritable change in DNA o So small so the cause change, must accumulate in biological lineages for billions of years o Major source of heritable variation o For most animals, only mutations in the germ line are heritable; mutations in other cell lineages have no direct effect on the next generation o Deleterious mutations alter an individual’s structure, function, or behavior in harmful ways o Advantageous mutation confers some benefit on an 4 individual that carries it. However slight the advantage, natural selection may preserve the new allele and even increase its frequency over time • Gene flow introduces novel genetic variants into populations o Occurs when organisms move from one population to another and reproduce to introduce novel alleles into the new population o Violates Hardy-Weinberg because not closed to migration o Researchers use phenotypic or genetic markers to identify immigrants in a population, but they must also demonstrate that immigrants reproduced, thereby contributing to the gene pool of their adopted population o When adult females do change populations, it is often late in the breeding season, and their offspring have virtually no chance of finding enough food to mature, thus, many immigrant females do not foster gene flow because they do not contribute to the gene pool of the population they join • Genetic drift reduces genetic variability within populations o Chance events causing allele frequencies in a population to change unpredictably o Dramatic effects on small populations because only a few individuals contribute to the gene pool and because any given allele is present in very few individuals, which violated Hardy-Weinberg assumption of infinite population size o Population Bottlenecks – stressful factor kills a great many individuals and eliminates some alleles from a population o Founder Effect – when a few individuals colonize a distant locality and start a new population, they carry only a small sample of the parent population’s genetic variation o Conservation Implications – without variation, no matter how large a population may become in the future, it will be less resistant to disease or less able to cope with environmental change • Natural Selection shapes genetic variability by favoring some traits over others o Although it can change allele frequencies, it is the phenotype of an individual organisms, rather than any particular allele, that is successful or not 5 o Relative fitness is the number of surviving offspring that an individual produces compared with the number left by others in the population o Directional selection – shifts a trait away from mean and toward the favored extreme o Stabilizing selection – individuals expressing intermediate phenotypes have the highest relative fitness o Disruptive selection – extreme phenotypes have higher relative fitness than intermediate phenotypes • Sexual selection often exaggerates showy structures in males o Intersexual selection – interactions between males and females o Intrasexual selection – males fighting males o Sexual dimorphism – differences in the size or appearance of males and females • Nonrandom mating can influence genotype frequencies o Inbreeding – individuals that are genetically related mate with each other o Increases frequency of homozygous genotypes and decreases heterozygous Diploidy Can Hide Recessive Alleles from the Action of Natural Selection • Recessive alleles can be protected from natural selection by the phenotypic expression of the dominant allele, at low frequencies and large populations • In small populations, a combination of natural selection and genetic drift can eliminate harmful recessive alleles Natural Selection Can Maintain Balanced Polymorphisms • Two or more phenotypes are maintained in fairly stable proportions over many generations • Heterozygous advantage – a balanced polymorphism can be maintained by heterozygote advantage, when heterozygotes for a particular locus have higher relative fitness than ether homozygote • Selection in varying environments – different alleles favored in different places or at different times, so genetic variability maintained 6 • Frequency-dependent selection – rare phenotypes have higher relative fitness than more common phenotypes Scientists Construct Hypotheses about the Evolution of Adaptive Traits • An adaptive trait is any product of natural selection that increases the relative fitness of an organism in its environment • Adaptation is the accumulation of adaptive traits over time Chapter 18: Species Definition of Species • Biological species concept defines a species as a group of organisms that can successfully interbreed and produce fertile offspring o Doesn’t work with species that reproduce asexually (androdioecous species, gynogenetic species) o Doesn’t apply where there is hybridization o Asexually reproducing populations had a higher frequency of mutations in mitochondrial protein-coding genes that sexually reproducing populations • Phylogenetic species concept defines a species as a group of organisms bound by a unique ancestry • Ecological species concept defines a species as a group of organisms that share a distinct ecological niche • Morphological species concept is the idea that all individuals of a species share measureable traits that distinguish them from individuals of other species Ring Species: Genes Flowing Between Some Populations • Ring-shaped geographic distribution that surrounds uninhabitable terrain • Adjacent populations can exchange genetic material directly, but gene flow between distant populations occurs only through intermediary populations Clinal Variation: Change Along a Gradient • Cline – pattern of smooth variation along the geographic gradient • Exhibited when a species is distributed over a large, environmentally diverse area • Result from gene flow between adjacent populations that are each adapting to slightly different conditions 7 Prezygotic Isolating Mechanisms: Isolation Before Fertilization • Mechanisms that prevent interspecific matings or fertilizations and the production of hybrid offspring include ecological (different habitat), temporal (mate at different times of the day/year), behavioral (signal differences), mechanical (structure of copulatory organs differ), and gametic isolation (incompatibility between sperm and egg) Postzygotic Isolating Mechanisms: Barriers After Fertilization • Reduce the fitness of hybrid individuals • Hybrid inviability can occur because many genes govern the complex processes that transform a zygote into a mature organism • Hybrid sterility results when parent species differ in the number or structure of their chromosome, which cannot pair properly during meiosis • Hybrid breakdown is when the next generation produce may exhibit reduced survival or fertility Geography of Speciation Allopatric Speciation: New Species Develop from Isolated Populations • Can occur when a physical barrier subdivides a large population or when a small population becomes separated from a species’ main geographic distribution • Occurs in two stages – first, two populations become geographically separated, preventing gene flow. Then, accumulate genetic differences that isolate them reproductively Parapatric Speciation: New Species Develop When Populations Span a Barrier • Speciation arising between adjacent populations; may occur if hybrid offspring have low relative fitness Sympatric Speciation: New Species Develop in Contiguous Populations • Reproductive isolation evolves between distinct subgroups that arise within one population • Changes in diet, behavior, or chromosomes could effect reproductive isolation, not geography or environment • Host race could be formed by individuals that were mutated to change their choice of host plant • Mate choice may not play a role but temporal and ecological 8 isolation is enough to separate the adults but still not sure that they are reproductively isolated Genetic Mechanisms of Speciation Genetic Divergence: When Isolated Pockets Develop in Continuous Populations • The amount of genetic divergence necessary for speciation to occur varies widely on the species and the type of reproductive isolation Polyploidy: Multiples of Haploid (N) Chromosomes • Common among plants where it plays an important role in diversification and speciation • Autopolyploidy o Chromosome duplications within a single species o Occurs through error in either mitosis or meiosis, so that gametes spontaneously receive the same number of chromosomes as a somatic cell, tetraploid is made o Tetraploid offspring can reproduce either by self-pollination or by breeding with other tetraploid individuals o 3n offspring are sterile because the odd number of chromosomes cannot segregate properly during meiosis o Tetraploid is reproductively isolated form the original diploid population • Allopolyploidy o Two closely related species hybridize and subsequently form polyploidy offspring o The hybrid’s non-homologous chromosomes wont pair properly during meiosis, a spontaneous doubling produces polyploidy condition with homologous chromosomes, and the hybrid can establish a new species if it can produce polyploid gametes through self-fertilization or fertilization with other doubled hybrids o New species in one generation – rapid Chromosome Alterations Can Lead to Genetic Isolation and Speciation • Inversions, translocations, deletions, and duplications may foster Postzygotic isolation • Evolutionary divergence can be reflected by the position of the centromere 9 • Proteins evolved more than twice as quickly in rearranged chromosome segments because it inhibits chromosome pairing and recombination during meiosis • New genetic variations favored by natural selection would be conserved within the rearranged segments and would accumulate over time, contributing to genetic divergence between populations with the rearrangement and those without it Chapter 19: Evolution and Classification Systematic Biology: An Overview • Two major goals: 1. To reconstruct the phylogeny or evolutionary history of a group of organisms o Phylogenetic trees are formal hypotheses identifying likely relationships among species o Tough phylogenetic hypothesis allow us to distinguish similarities inherited from a common ancestor from those that evolved independently in response to similar environments 2. Taxonomy, the identification and naming of species and their placement in a classification o A classification is an arrangement of organisms into hierarchical groups that reflect their relatedness o Most want classifications to mirror phylogenetic history and thus, the adaptive radiation oh the group of organisms The Linnaean System of Classification • Named on the basis of similarities and differences • Taxonomic hierarchy for arranging organisms into ever more inclusive categories • Family – group of genera that closely resemble one another • Similar families grouped into orders, similar orders grouped into classes, similar classes grouped into phyla, similar phyla grouped into kingdoms, and all grouped into 3 domains Evaluating Systematic Characters • Systematists seek characters that are independent markers of underlying genetic similarity and differentiation because different organismal characters can have the same genetic basis 10 • They create phylogenetic hypotheses and classifications by analyzing the genetic changes that caused speciation and differentiation • Often must rely on phenotypic traits as indicators of genetic similarity or divergence but try to exclude differences caused by environmental conditions • Analyses rely on comparison of homologous characters (same basic structural elements with similar spatial relationships to each other and to the bones that attach to the rest of the skeleton; emerge from comparable embryonic structures and grow in similar ways during development) as indicators of common ancestry and genetic relatedness • Analogous characters are homoplasious phenotypic similarities that evolved independently in different lineages (similar function in different species) • Systematists exclude homoplasies from analyses because they provide no information about shared genetic ancestry • The distinction between parallel and convergent evolution is based on closeness of relationships • Mosaic evolution refers to the reality that in all evolutionary lineages, some characteristics evolve slowly, whereas others evolve rapidly • Ancestral characters are old forms of traits and derived characters are new forms of traits • Derived characters provide the most useful information because once a derived character becomes established, it is usually present in all of that species’ descendants (serve as markers for lineages) • Outgroup comparison is used to identify ancestral/ derived characters by comparing the group under study with more distantly related species not otherwise included in the analysis Phylogenetic Inference and Classification • Monophyletic taxa is those derived form a single ancestral species • Polyphyletic taxa includes species from separate evolutionary lineages • Paraphyletic taxon includes an ancestor and some but not all of its descendants • Parsimonious phylogenetic hypotheses include the fewest possible evolutionary changes to account for the diversity within 11 a lineage • The justification is the assumption of parsimony which states that the simplest explanation should be the most accurate; meaning that any particular evolutionary change is an unlikely event and presumably happened only once in any evolutionary lineage and it is unlikely that the same change evolved twice in one lineage Traditional Evolutionary Systematics: Using Phenotypic Similarities and Differences to Classify Organisms According to Their Evolutionary History • This approach groups together species that share ancestral and derived characters • This reflects evolutionary branching and morphological divergence • Each classes (amphibian, Mammalia, reptilian, and aves) are given equal ranking because each represents a distinctive body plan and way of life Cladistics: Classification Based on Shared Derived Characters • Argued that classifications should be based solely on evolutionary relationships • Groups together species that share derived characters • Argue that mammals form a monophyletic lineage (a clade) because they have a unique set of derived characters • Ancestral characters do not distinguish well enough so are not considered • Cladogram (phylogenetic trees) include a hypothetical ancestor at each branching point and use the principle of parsimony Chapter 20: Darwin, Fossils, and Developmental Biology Recognition of Evolutionary Change • Buffon (comparative morphology) said animals have changed since their creation - Vestigial structures are the useless body parts we observe today that must have functioned in ancestral organisms; “conceived by nature and produced by time” • Cuvier (geology) suggested that abrupt changes between geologic strata marked dramatic shifts in ancient environments. Then developed the theory of catastrophism, reasoning that each layer of fossils represented the remains of organisms that had died in a local catastrophe, different species recolonized the area 12 and formed a different set of fossils in the next layer • Lamarck (biological evolution) proposed that a metaphysical “perfecting principle” caused organisms to become better suited to their environments. Simple organisms evolved into more complex ones and microscopic organisms were made by spontaneous generation. o Principle of use and disuse – body parts grow in proportion to how much they are used and unused structures get weaker and shrink o Inheritance of acquired characteristics – changes that an animal acquires during its lifetime are inherited by its offspring o These are false, but he proposed very important points:  All species change through time  Changes are passed from on generation to the next  Organisms change in response to their environments  Hypothesized the existence of specific mechanisms that caused evolutionary change Changes in Earth • Hutton (gradualism) argued that slow and continuous physical processes, acting over long periods of time, produced Earth’s major geological features (contrasted with Cuvier) • Lyell (uniformitarianism) argued that the geologic processes that sculpted Earth’s surface over long periods of time are exactly the same as the processes we observe today (undermined any remaining notions of an unchanging Earth) Charles Darwin • Primed to apply gradualism and uniformitarianism to the living world • Hypothesized that the plants and animals of the Galapagos were descended from South American ancestors and that each species had
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