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BIOL 1001
Hernan Humana

1 BIOL 1001 MIDTERM II NOTES Persephone Greco-Otto MICROEVOLUTION Genetic Variation, Mutation and Hardy-Weinberg Principle  Definitions: o Population = all individuals of a single species that live together in the same place and time o Micorevolution = small-scale genetic changes within populations, often in response to shifting environmental conditions/chance events (natural selection, genetic drift, gene flow) o Phenotypic variation = differences in appearance/function between individual organisms o Qualitative vs. Quantitative variation = variation that exists in 2 or more discrete states, with intermediate forms absent vs. variation that is measured on a continuum rather than discrete units/categories o Mean = average value of characteristic (changed by directional selection)  Variation: discrete (qualitative  either/or differences or continuous; quantitative  individuals differ in small, incremental ways), caused by genetics or environment, **only genetically based variation subject to evolution o Genetic variation  production of new alleles (mutations) or rearrangement of existing alleles (genetic recombination, independent assortment, random fertilization)  Importance of variation in populations for evolution: more genes that code for possibly advantageous phenotypes, thus making the population stronger  Why 2 individuals of the same species can have different genotypes but the same phenotype and vice versa: phenotype also influenced by environmental factors, interaction between genes and environment (environment can influence gene expression), some variations in DNA don’t change the amino acid sequence so no change in phenotype  Interpret from a graph of a quantitative character, the degree of variation for that character within the population: broad, low curve  a lot of variation; high, narrow curve  little variation (width of curve is proportional to variability)  Mutations = heritable change in DNA o Random  not acquired because they are seen as advantageous (eg. deleterious mutations alter an individual in harmful ways, lethal mutations cause death, neutral 2 mutations neither harmful nor helpful), but occur randomly and accumulate if advantageous **in most animals, only mutations in the germ line (gametes) are heritable o Vertical vs. Horizontal inheritance = The transmission of traits from parent to offspring vs. transmission not between parents/offspring (independent of reproduction)  Definitions: o Pseudogene = mutations may prevent expression o Gene family = genes similar to each other in structure and function o Evolutionary developmental biology (evo-devo) = how evolutionary changes in genes regulating embryonic development can lead to changes in body shape and form (embryos of different species compared), changes expression pattern (underlies evolution of morphological innovations) o Genetic tool kit = homeotic genes (regulatory genes that code for transcription factors that bind regulatory sites on DNA  activate/repress expression of genes), governs basic design of body plan (at precise tines in a precise way), some of the genes are from earliest forms of life  Hox family genes  body plan, specify where appendages attach  Pax 6  formation of light sensing organs (eyes)  Pitx 1  presence/absence of spines  **most animals share the same tool kits  different body plans caused by mutations (diff. expression of genes in diff. body regions at diff. time)  Accumulated mutations create NEW genes  Gene duplication o Outcomes of Gene Duplication  1. Duplicated genes retain original function (provide additional quantities of same product) 3  2. May retain original function, but change in expression pattern  Duplicated gene gains mutations  altered protein products could perform valuable new function  Mutation may prevent expression (pseudogene)  Fins to Fingers  Early embryonic development same  buds of mesoderm, elongate and cartilage deposited at localized centres  Fish  bones develop along central axis, HoxD genes become active in cells posterior to the central axis of the fin  Tetrapods  bones (limb and digits) develop along central axis, HoxD genes first become active in cell posterior to the central axis, then active in band of cells perpendicular to the central axis of limbs o Gene pool = the sum of all alleles at all gene loci in all individuals in a population o Genotypic frequency = percentage of individuals in a population possessing a particular genotype o Allele frequency = abundance of one allele relative to others at the same gene locus of individuals of a population o Relative abundance =*** o Genetic equilibrium = the point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations o Loci/locus = every locus displays variation, 2 alleles at every locus o Fixation/loss =***  How small genetic changes account for large changes in characteristics and lead to new morphologies: changes in genetic code can change the protein that is produced, resulting in an entirely different morphology  Genotypic vs. allele frequency = genotype frequency is the percentages of individuals possessing each genotype; allele frequency represents commonness/rarity of each allele in the gene pool o Calculations: since all diploid organisms have 2 alleles at each locus, 1000 individuals would have 2000 alleles at a particular locus.  Genotype frequency = # of individuals/total population  Total number of homozygous = 2 x # of individuals  Allele frequency = # of alleles/total # of alleles 4 • Hardy-Weinberg Principle: o Acts as a null model/hypothesis for evolution, genetic equilibrium, p²+2pq+q² = 1 o 5 Conditions  1. No mutations  2. No migration  3. Population infinite in size  4. All genotypes survive and reproduce equally well  5. Random mating o No micorevolution NATURAL SELECTION & ADAPTATION  Definitions: o Natural selection = the evolutionary process by which alleles that increase the likelihood of survival and the reproductive output of the individuals that carry them become more common in subsequent generations (importance of genetic variation, how natural selection acts on phenotypic variation to alter the genetic structure of a population, not random, leads to adaptations in populations) o Artificial selection = selective breeding by humans of individuals with favourable traits (provides evidence for natural selection) o Adaptation = characteristic(s) that help an organism survive longer/reproduce more under a particular set of environmental conditions o Fitness = the ability of an individual to produce offspring relative to the ability of other individuals within the population to produce offspring o Relative fitness = the number of surviving offspring than an individual produces compared with the number left by others in the population o Limitations to fitness:  Females  ability to gain resources to produce more eggs/healthier young (protect investment by being choosy about mates)  Choice based on: honest signals of male, resources/parental care provided by male  Males  # of females can mate with o Stabilizing selection = type of natural selection in which individuals expressing intermediate phenotypes have the highest relative fitness, BUT no change in average value of trait over time, reduction of genetic diversity 5 o Directional selection = a type of selection in which individuals near one end of the phenotypic spectrum have the highest relative fitness o Disruptive selection = type of natural selection in which extreme phenotypes have higher relative fitness than intermediate phenotypes o Polymorphism = 2 or more phenotypes are maintained at in fairly stable proportions over many generations, when heterozygotes have higher fitness o Fitness trade-off = compromise between traits in terms of how those traits perform in environment, selection acts on many traits at once, may help attract a mate but also predators, etc o Adaptive radiation =** o Descent with modification = ancestral alteration and diversification, biological evolution, all organisms arose through DWM  Importance of reproduction in evolution by natural selection: in order for natural selection to shape evolution, organisms must live long enough to produce offspring, who must also produce offspring. Evolution by natural selection is a slow process that spans over many generations.  Evolution is not progressive and there are limits to adaptive evolution: evolution is not necessarily beneficial since mutations
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