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LO's midterm 2.docx

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York University
BIOL 1001
Tamara Kelly

Learning objectives – midterm 2 LEARNINGOBJECTIVES: MICROEVOLUTION 1. Provide arguments supporting evolution as a population process, explaining why individuals do not evolve. [Comprehension] • Evolutionary change is based on changes in the genetic makeup of populations over time. Populations, not individual  organisms, evolve. Changes in an individual over the course of its lifetime may be developmental (e.g., a male bird  growing more colorful plumage as it reaches sexual maturity) or may be caused by how the environment affects an  organism (e.g., a bird losing feathers because it is infected with many parasites); however, these shifts are not caused  by changes in its genes 2. Justify the importance of genetic variation in populations to the process of evolution, explaining the ways in which variation is generated. Given a scenario/graph classify: the degree of variation for that character, variation as qualitative or quantitative. [Comprehension, Application, Analysis] • Variation is important because it is a strong contributor to evolution. Through variation within a population individuals vary in genetics. If genotypic, these more advantageous variation will be favored by natural selection, this resulting in the increase of the frequency (allele) of these traits. Thus through evolution (microevolution) overtime these changes can result in it becoming the dominant in the population. Basically without variation, natural selection would have nothing to favor and pass on (no advantageous trait) = no evolution (everyone stays the same) • Production of new alleles:  mutations • Rearrangement of existing alleles:  crossing over (during meiosis); Shuffles segments on the chromosomes  independent assortment (arrangement along metaphase plate); shuffle whole chromosomes (each homologous pair shuffles independently) random fertilization between egg and sperm • We display data on quantitative variation in a graph; the width of the curve is propotional to the variability (amount of variation) amongst individuals. o A broad, low curve indicates a lot of variation among individuals. o A high narrow curve indicates little variation among individuals • Quantitative: gradual continuum of variation in a trait. Ex height, weight, skintones, # of hair • Qualitative: discrete variations in traits, no intermediates. Ex snow geese are either blue or white 3. Given a scenario (e.g., the number of individuals with a specific genotype), calculate frequencies of alleles, genotypes, and phenotypes, starting with the number of individuals of a specific genotype or phenotype, or the frequency of an allele. Use information as to whether a population is in HWE to solve a problem. [Application] • Gene pool: the sum of all alleles at all genes loci in all individuals in a population • To describe the structure of a gene pool, scienctists first calculate genotype frequencies: the percentages of individuals possessing each genotype ECX C C = 500 R W indiv  0.5 C R R 450 indiv  0.45 => 0.5+0.45+0.05 = 1 C W W 50 indiv  0.05 /1000 • Knowing that each diploid organism has two alleles (either two copies of the same or two different allele ) at each gene locus, a scientist can calculate- Allele frequency: the abundance of one allele relative to others at the same gene locus with two alleles there are 3 genotype frequencies (pq, pp, qq (sum of 3 gene frequencies must equal 1), but only two allele frequencies (p and q (sum of these 2 allele frequencies must equal 1) EX p= CR(600 x 1) + (450 x 2) + (50 x0) = 1400 / 2000 alleles = 0.7 Q= CW(500 x1)+ (450 x 0 ) + (50 x 2) = 600/ 2000 alleles = 0.3  p+q = 0.7+0.3 =1 • Relative abundance: the relative commonness of population within a community (alleles with genelocus) • Genetic equilibrium: the pt at which neither allele nor genotype frequencies in a population change in succeeding generations • Loci/locus: a particular gene location on a chromosome  in diploids, each locus has 2 alleles (in diploid organisms ( have 2 pairs of homologous chromosomes) an individuals genotype includes two alleles at every gene locus) • Fixation/loss: alleles with a frequency of 1 are fixed: lost have frequency of 0 • WATCH BOZMON SCIENCE VIDEOS ON IT 4. Explain how the Hardy-Weinberg (HW) principle acts as a null hypothesis/model for evolution, relating the assumptions/conditions of HW to the mechanisms of evolution, and populations to which HW is applicable. Given a description of a population, indicate whether any (and which) of the assumptions have been violated. [Comprehension] • The hardy-weinberg principle (is a null model): 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) o Null model since it shows when evolution, which changes allele frequencies, doesn’t occur  Reference point in which evaluating circumstances under which evolution may occur o P +2pq+Q ; HW principle acts as a null hypothesis because it demonstrates an ideal situation where no evolution is occurring (studies that use observational experiment use this instead of a control variable) • Hw; is a null model that describes the conditions under which microevolution will not occur: o No mutation occurring o No gene flow: no emigration or immigration to the gene pool o Random mating with respect to the gene in question o No genetic drift, or random allele frequency changes, affecting the gene in question: alleles are drawn in their exact frequency. Not by values caused by chance o No natural selection at the gene in question: population survive and reproduce equally well • Microevolution will not occur under HW conditions because no new alleles through mutation, all survive  allele frequency never changes. Thus, can be no change in genetic makeup of population. • All the above points are mechanisms of evolution and if there is no change in mechanism of evolution then there is no evolution or change in gene pool frequencies 5. Describe the mechanism of evolution by natural selection, explaining why evolution is not progressive (i.e., moving towards ‘perfection’), how natural selection is non-random and results in adaptations. [Comprehension] • Evolution does not progress towards perfection cause evolution operates via chance occurences. Like mutations and random fluctuations in population, and by natural selection. Mutations and random events (i.e., a huge volcano explodes and vaproizes a population indiscriminately) are clearly not progressive events. They’re random.  natural selction works by creating filter through which the organisms that are most fit, leave the most offspring. Environments change constantly and since natural selection only promotes adaptations to the conditions immediately at hand, it is not progressive. Evolution has no foresight • The genetic variation that occurs in a population because of mutation is random — but selection acts on that variation  in a very non­random way: genetic variants that aid survival and reproduction are much more likely to become common  than variants that don't. Natural selection is NOT random! • Selection occurs based on alleles (traits) they have ▯ the more fit, the more likely for the allele to be selected for  (natural selection is not random in that it selects for specific individuals who possess traits advantageous to them o Adaption: is the accumulation of adaptive traits over time o Adaptive trait: is any product of natural selction that increases the relative fitness of an organism in its environment a. Describe how natural selection acts on phenotypic variation to alter the genetic structure of a population. [Comprehension] • Specific phenotypes selected by natural selection thus genotype for it selected  more common in population. It is the phenotypic differences which determine whether an individual is advantageous over another. Phenotypic variation include being faster, stronger, having better eyesight. Natural selection than favors those advantageous traits and the traits chosen are then increased in the next generation causing the genetic structure of the population to change 1. Differentiate between the various types of selection (e.g., directional) and their effects (e.g., genetic variation, mean character value) on a population (either alone or in tandem) over a period of time. Given a scenario, determine the type(s) of selection acting and predict the effects on the population. [Knowledge, Comprehension, Application, Analysis • Stabilizing selection: type of natural selection in which individuals expressing intermediate phenotypes have the higher relative fitness (By eliminating phenotypic extremes, stabilizing selection reduces genetic and phenotypic variation and increases the frequency of intermediate phenotypes) Stabilizing selection, affecting many familiar traits. Ex. Very small or large human newborns are less likely to survive than those born at an intermediate mass. • Directional selection: type of natural selection in which individuals near one end of the phenotypic spectrum has the highest relative fitness. (Directional selection shifts a trait away from the existing mean and toward the favored extreme. After selection the traits
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