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lecture outcomes

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Biology 1002B
Tom Haffie

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Lecture Outcomes 12-24 Lecture 12  General pathway of eukaryotic membrane protein production • Two homologues start in the nucleus • The alleles get transcribed and spliced, the transcripts leave the nucleus and attract the ribosomes, which take them to the ER • The transcripts are translated on the ER and are packaged into vesicles that go to the golgi that are packaged into new vesicles that are sent to the membrane  General physiology of skin/hair pigmentation. • Pigment production results from the production of melanin • There are two types of melanin  Black (Eumelanin) and Red (red yellowy) (Pheomelanin) • Melanin is produced by melanocytes and pack into melanosomes that get exported it out into the skin cells and hair follicles cells  Characteristics of dominant alleles. • Determines the phenotype of an organism • Dominance depend on what other allele it is paired with  Which allele in a heterozygote is dominant, given the biochemical mechanism of action of allele products? • DNA with a black and brown allele for skin pigmentation • The black allele is on all the time, and the brown one is on only some of the time  Since the black allele is always on the AMP levels are always high • Therefore the black allele is dominate because it determines the phenotype  Factors that affect how allele frequencies change over time in a population. • The allele frequency will not change much when the dominant allele is common and the recessive allele is rare • The allele frequencies will not change much when the recessive allele is common and a dominant allele is rare • The frequencies of the starting allele frequencies is what influences the future allele frequencies (It does not matter what the dominant allele is)  Allele frequencies (p and q), given genotypic frequencies. • 60% bearing Brown allele (W) and 40% bearing the Red allele (R) • WW (6x6=36) WR (6x4=24) RW (4x6=24) RR (4x4=16)  Product rule • P , pq, q2  Function of various MC1R alleles. • Membrane receptor alleles • High cyclic AMP cells melanocytes produce Black melanin • Low AMP levels Red melanin is produced Lecture 13  Conditions necessary for Hardy-Weinberg equilibrium • No mutations are occurring • The population is closed to migration from other populations (gene flow) • The population is infinite in size (large) • All genotypes in the population survive and reproduce equally well • Individuals in the population mate randomly with respect to genotypes  Whether a population is in HWE, given observed genotype or phenotype frequencies • If genotype frequencies can be predicted from allele frequencies = HWE • Look at the p, q, and pq values • Heterozygotes should have a higher frequency than recessive or dominant • P doesn’t have to equal q for the population to be in HWE  Effect of selection on changes in allele frequency • If selection pressure is weak then evolution proceeds slowly but allele frequency will still decrease • If selection pressure is high then evolution will proceed quickly and decrease the allele frequency  Relative vs absolute fitness • Absolute lifetime fitness (W) is the average of the fitness of the whole population with the same genotype, counting up units of offspring or the length of time in years that an individual lives • Relative fitness is taking into consideration the level of fitness compared to the other fitness levels the fittest of all the genotypes is assigned the level of 1  How to calculate relative fitness • W (absolute fitness)/W maxthe fittest absolute value) = w  How to quantify strength of selection • By looking at the relative fitness; the greater the relative fitness then the stronger selection is going to be  Relationship between dominance/recessiveness of alleles and response to selection. • When selection is against the dominant allele it disappears • When selection is against the recessive allele it decreases in frequency but it doesn’t disappear • Dominant allele has high fitness it will level off and never completely outcompete the recessive allele (sheltered in the heterozygote)  Effect of heterozygote advantage on genetic variation • Heterozygotes hide the recessive allele • Heterozygotes contain a good allele, so their personal fitness is just fine • Dominance constrains selection  Why the amount of genetic variation in a population is important • If it lacks variation it cannot adapt to a changing environment • Important on the individual level because of inbreeding depression (individual fitness)  Different types of selection (stabilizing, directional) and their effect on genetic variation • Stabilizing: most dominant form of selection in most populations, the highest fitness is a medium favoured trait (center of the distribution) Ex. Human birth weight • Directional: the individuals at one extreme of the distribution are selectively favoured (shift of the mean value) Ex. Long tailed birds Lecture 14  Effect of various types of selection on amount of variation in a population. • Selection is the only force that can cause a population to become adapted to its environment, but not the only thing that can cause it to evolve • Adaptations: traits that increase bearer’s relative fitness, are environment- specific and relative • Genetic Drift: decrease variation within a population, increase among populations  Examples of stabilizing, directional, disruptive. • Disruptive: opposite of stabilizing, individuals at either extreme are favoured, no change in mean value but a discontinuity in distribution Ex. Darwin’s Finches  Reasons why directional selection does not remove all genetic variation from a population. • The environment is always changing • Some alleles because recessive can remain in the population • Not all populations experience directional selection in the same direction for a period of time: spatial variation  Selection pressures are not always uniform (patchy) for the entire range of the population (phenotype may have high fitness in one part of the range, but not in the other) Ex. Peppered moth  Characteristics, and examples, of frequency dependent selection. • Negative frequency-dependence: there is an advantage to being rare  Predators form search image to look for the species if you’re rare you won’t be spotted  Results in both the alleles being maintained, in balance • Positive frequency-dependence: there is an advantage to being the most common  Warning colouration of frogs  Reasons why all living things are not perfectly adapted to their environment. • The environment is always changing so the organism is always trying to adapt  Adaptation is always one generation behind the environmental changes  If the environment is rapidly changing the organism might not be well adapted • Selection might not choose the perfect allele  Genetic variation: because the perfect allele hasn’t shown up through mutation • Gene flow and genetic drift may keep entering the population or disappear • Traits often offer compromise when distinguishing a trait  Widow bird needs to attractive females and be able to fly (tail not too long)  Effect of genetic drift on allele frequencies within a population, particularly in the case of bottlenecks etc. (Nonadaptive evolution) • Random, unpredictable changed in allele frequencies due to sampling error  Drift is the strongest in small populations (bottlenecks, founder)  One allele goes to fixation and the others are lost • Drift opposes selection: outcome depends on the strength of selection/population size  Effect of genetic drift on variations between populations. • Decrease variation within population • Increases variation among population because different alleles would go to fixation  Mechanism that explain why mutation is NOT directed toward the needs of the organism. • Most mutations have neutral or nearly-neutral effects on fitness • Mutations are always happening whether the organism needs it or not • Of those that affect fitness, most are harmful • Mutation often opposes selection but provides raw material for adaption  Why most mutations that affect fitness are harmful. • Easier to break something than to stumble across an innovation that improves it  Effect of gene flow on allele frequencies. • Introduces new alleles and often opposes selection (selection-migration balance) • Prevents populations from becoming perfectly adapted to their environments  Characteristics of adaptive vs. non-adaptive mechanisms affecting allele frequency. • Adaptive: selection • Nonadaptive: Frequency dependent selection, genetic drift, mutations, gene flow  How various evolutionary forces reinforce or oppose one another. • Mutations, gene flow, genetic drift often opposes selection Lecture 15  Types of non-random mating • Inbreeding OR inbreeding avoidance: avoiding mating with people who are related to you (similar genotypes), but sometimes they like to mate with close relatives • Assortative OR disassortative mating: depending whether like mating with like or opposites attracting  Ex. Assortative mating = white geese mate with white geese  Ex. Disassortative mating = sparrow mates with different coloured plumage  Effect of non-random mating on HWE and on evolution • Nonrandom mating perturbs HWE, but does not cause evolution (no change in allele frequencies)  Characteristics of a scientific theory • A coherent set of testable hypotheses that attempt to explain facts about the natural world; assertions that cannot possibly be falsified are not scientific • True: an assertion for which there is so much evidence that is would be perverse to deny it, we have to test it many times to see if our predictions are contradicted • Theories ‘graduate’ to fact-hood after repeated testing fails to falsify them  Components of the theory of evolution • Evolution happens: change in allele frequencies in a population, between generations • Most evolution is gradual: Over many steps, many years of tiny changes can it be seen • Speciation happens: all life has evolved from a single common ancestor and over evolutionary times there are many times when a single lineage splits into two or more lineages that become reproductively isolated from each other • All life is related through ancestry: for any two species we should be able to trace lineages and find MRCA • Much of evolutionary change is caused by selection • Evolution occurs in populations, not within individuals: evolution acts on the variation already in the population: population change but individuals do not adjust in response to selection  Evidence for "descent with modification" • Homologies: relations through structure, developmental, molecular = shared ancestry  Similarity between two species, not explainable by shared function • Transitional forms: fossils show that we descended from each other (Grey Whale)  Examples of homology and why they support the idea of evolution • The genetic code is the same for all organisms • The finger bones are similar in birds, bats, humans etc.  Examples of vestigial traits and why they support the idea of evolution • Only make sense in the context of evolution • Something that the organism doesn’t need or use but they still have • They must have had an ancestor who did need these traits (dandelion)  Role of fossil record as evidence for evolution • Fossils show intermediate bone structure for organisms the grey whale and the different placement of the nostrils Lecture 16  Relationships among sexual reproduction, meiosis and genetic variability • Recombination gives rise to genetic diversity (crossing over, independent assortment) • Offspring are different from their parents, and usually each other  Mechanisms of asexual reproduction • Bacteria and archaea reproduce by binary fission • Plants can send out runner to give rise to new clones • Aspen trees have option to reproduce sexually or asexually  Examples and predictions of size-advantage model of sex change • Different selection pressures on males and females • Could be an advantage to being small or large and the fitness function for males and females could differ and when they reach the same point of fitness they cross over to the sex that has the higher fitness (protandry)  Distribution of sexual reproduction among all life forms, and particularly among animals • Sexually reproducing organisms may be dioecious (male or female function) or monoecious (male and female function in one organism, is more common in flowers) • Sequential monoecy (sex change): some animals change sex depending on conditions • Vast majority of life reproduce asexually • The dominant mode of reproduction for animals is sexual reproduction  Costs of sexual reproduction • It is timely and takes your attention away from other thing in order to find a mate  Cost of meiosis • You are only passing on half your genes in the next generation no very efficient  Cost of sons • Females who produce only daughters asexually, then females who reproduce asexual will out-compete the females who reproduce sexually  "Muller's Ratchet" mutational load explanation for advantage of sexual reproduction • For a species that reproduces asexually should continue accumulating harmful mutations because there is no way of getting rid of harmful mutations = extinction • Sex breaks this “ratchet” by fixing these harmful mutations  "Ruby in the Rubbish" hypothesis explanation for advantage of sexual reproduction • Every time you reproduce sexually you are gambling, sometimes it works out well and other times the offspring reproduced may have more harmful mutations • Increases the variation in fitness  Combination of beneficial mutations for advantage of sexual reproduction • Sex can speed up the rate at which beneficial mutations occur in the same individual • Randomly matting then there is a good chance some individuals in the next generation will get two and three helpful mutations and that genotype will have extremely high fitness and reproduce faster spreading the high fitness  Relationship between extinction rate and sexual reproduction • Sexual reproduction decreases the rate of extinction, almost all of the asexually reproducing animals are recent evolutionary origin • Asexually reproducing species go extinct very fast because we don’t have ancient organisms Lecture 17  “lottery ticket hypothesis” and “red queen hypothesis” to describe the relationship between environmental stability and benefits of sexual vs. asexual reproduction • LTH: the environment is always changing so sex is constant; just because I am adapted to the environment doesn’t mean that a future ‘me’ will also be adapted • RQH: sex is favoured when your environment (natural enemies) is continually evolving  Long-term vs. short term advantages to sexual vs. asexual reproduction • Selection does not favour traits that benefit long-term persistence of ‘the group’ at the expense of immediate individual fitness • Long term: removing harmful mutations, combining helpful mutations • Short term: bet-hedging in a changing environment • Reduce extinction risk may be just a consequence of sex, not an explanation  Why sex places different selective forces on males vs. females • Because males need to increase their fitness by having many offspring • Females focus more on the quality of their offspring  Role of parasites as an explanation for the persistence of sexual reproduction • By having sexual reproduction there is a greater variance of fitness and when parasites are present they could kill off a whole species if there wasn’t variance  How sexual selection maintains traits seemingly incompatible with natural selection • Some trait may be a disadvantage to a species natural selection wise but it is advantageous when attracting a mate, so it is maintained because it gives the animal fitness because by mating it is able to pass its genome on to the next generation  Examples of traits favoured by intra vs. inter sexual selection • Intersexual selection: female choice the dancing bird, males compete with each other for the females • Intrasexual selection: males will sabotage other’s males bowers  Why males are more usually competing for access to females (rather than vice versa) • The more females the male mates with the more he is increasing his fitness (more offspring)-male has a higher potential fitness so is chosen • Females are limited by the number of offspring they can produce, so they are focused on increasing offspring quality  Relationship between parental investment and which sex is c
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