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Biology 1001A
Beth Mac Dougall- Shackleton

12/5/2012 9:01:00 PM general pathway of eukaryotic membrane protein production. general physiology of skin/hair pigmentation. characterisitics of dominant alleles. which allele in a heterozygote is dominant, given the biochemical mechanism of action of allele products. factors that affect how allele frequencies change over time in a population. allele frequencies (p and q), given genotypic frequencies. function of various MC1R alleles. If you breed a black with a brown what would happen? All black pigs in f1 In f2 > you get some of each but more black than browns. It stabilizes to 3:1. So the black allele is dominant of brown. The dna with the 2 diff alleles (homologues) in the nucleus, allele transcribed and get spliced.transcript leave the nucleus and attract the attention of ribosomes. Ribosomes take transcripts to the ER which get translated then packaged into vesicles that go to the golgi and then into new vesicles that send those proteins to cell membrane. Two different receptors on the cell because there is two different allele in the cell Pigment production results from the production of melanin, 2 kinds: black melanin and red/yellow melanin (no brown) melanin is produced by melanocytes and packed into sub cellular organelles called melanosomes, which get exported melanocytes pack melanosome with melanin then export it to skin cells and hait follicle cells > they will get pigmented. Brown is the mixture of red and black The protein MC1R (membrane receptor) sits in the membrane and makes black melanin if cyclec AMP levels are high. High cyclic amp makes black In response to hormone, cyclic amp levels fall and red melanin is produced instead So cells can make either one if just depends on cyclic amp levels So brown allele can switch on and off Cyclic amp levels are high all the time with B (black) allele. It is insensitive to hormones in the environment. In a hetrozygote, there is brown allele and black allele in the same cell. The receptors on the cells are two different types because there are two different alleles. Cyclic amp levels are always high because of the black allele > that is dominance because interaction with gene products Dominance occurs at the level of bio chemistry The active allele (black ) never inhibits the recessive one In heterozygotes, the allele that is on all the time, that is the one that determines the phenotype of the offspring therefore that is the dominant one. In homozygotes, the red allele is off all the time (cyclic amp levels are always low) The idea that there is an allele that is always dominant is not necessary Dominance and recessiveness happens between any two particular allele at a particular time Any allele isn‟t necessarily only dominant all the time. It depends on what the other allele its with in a hetrozygote In a population if a dominant allele is common and recessive allele is rare, the allele frequency doesn‟t change. If recessive allele is common and the dominant allele is rare, the allele frequency also doesn‟t change very much. The dominant frequency increases slightly In a large population, in the absence of selection, the starting allele frequency influences future allele frequencies. There is nothing inherent about dominance that causes it to increase in frequency in a population. The dominant allele is not necessarily the most fit allele in a population (not always increase in frequency) A recessive allele doesn‟t doom it to a noticeable decrease These are not in themselves sufficient enough to drive allele frequency. We use the punnet square in a large scale to make predictions of allele frequency and use the product rule to predict offspring genotype. 12/5/2012 9:01:00 PM conditions necessary for Hardy-Weinberg equilibrium whether a population is in HWE, given observed genotype or phenotype frequencies effect of selection on changes in allele frequency relative vs absolute fitness how to calculate relative fitness how to quantify strength of selection relationship between dominance/recessiveness of alleles and response to selection. effect of heterozygote advantage on genetic variation why the amount of genetic variation in a population is important different types of selection (stabilizing, directional) and their effect on genetic variation allele is recessive to another allele doesn‟t necessarily mean it will decrease in frequency. Evolution a change in allele frequency from one generation to the next. Mc1R- lots of different allele. To recognize whether a population is evolving (eg due to natural selection) we need something to compare it too > the conditions of HWE Population that very large, where mating is random, mutations are rare, no gene flow, and no selection on the population (all have equal fitness) then we can use the allele frequency of a population to calculate the expected genotype frequencies. > we get the HW proportions. Genotype frequencies are predictable through allele frequencies Classic HWE in a population for 2 alleles at a locus = 25% GG, 50% Gg, 25 25% gg Not all populations are in HWE.this tells you one or more of the conditions is not being met (it may be evolving) Even if two allele frequencies are equal, that doesn‟t determine that the population is in HWE Population is in HWE (no evolutionary forces are operating on the population) > allele frequency is not changing population from one generation to the next If expected allele frequency is different from observed allele frequency then the population is not in HW. > this means that one or more of the conditions in not being met. The population could be evolving. Dominance does interact with selection pressure When selection occurs on a dominant allele, it can wipe out that allele pretty fast. But selection against a recessive allele, there always gna be a copy of that recessive allele in a heterozygous individual. Heterozygotes have normal personal fitness because deleterious allele is recessive Dominant allele will reach a high final frequency (even heterozygotes have high fitness) but will never reach a frequency of 1. Deleterious rec allele will still exsist in a population because it is “sheltered” in heterozygotes Conversely, if there is a beneficial recessive allele that arise (a mutation) will eventually completely outcompete the unfavourable dominant allele and reach a frequency of 1. Dominance status allele does interact with natural selection and affect the ultimate outcome of selection. This explains why the vast majority of genetic disorders are associated with recessive allele. Theres hardly any genetic disorders associated with dominant allele. This is because if there were, natural selection would take them out of the population asap. Selection > most important evolutionary force in biology Different types of selection would have diff effects on the amount of genetic variation in a population . Genetic variations meant by how many diff alleles are there in a population. Another measure is hetrozygoucity. What proportion of indivisuals in the population are heterozygotes at a given locus Why do we care about genetic variation (long term and short term) > if a population lack genetic variation it can not adapt to a changing environment. Its also important at an individual level. Inbreeding depression > offspring of close relatives have low fitness because Deleterious recessive allele. If selection favoured heterozygotes. Both alleles will be maintained in the population in equal frequency. Selection without evolution >> hetrozygote advantage.(because allele frequency is not changing) The vat majority of traits is not governed ( that affect fitness) by a single locus rather quanitative traits distribution. Selection have affect on genetic variation as well as population mean value for the trait under selection Most traits that are under stabilizing selection the most common form of selection. Eg. Baby birth weights..The individuals with extreme phenotypes (smaller or lager than average) have low survivorship than those that had the average value. Directional selection > the indivisuals at one extreme are favoured. This causes a shift in the population mean value, unlike the stabilizing selection where mean value stays the same and the variation (scatter) around that in terms of the phenotypes shrinks Directional> favours indivisuals with an extreme (eg. Tail length) Directional selection eventually become stabilizing selection? Yes. 12/5/2012 9:01:00 PM effect of various types of selection on amount of variation in a population. examples of stabilizing, directional, disruptive. reasons why directional selection does not remove all genetic variation from a population. characteristics, and examples, of frequency dependent selection. reasons why all living things are not perfectly adapted to their environment. effect of genetic drift on allele frequencies within a population, particularly in the case of bottlenecks etc. effect of genetic drift on variations between populations. mechanism that explain why mutation is NOT directed toward the needs of the organism. general fitness effects of mutations. why most mutations that affect fitness are harmful. effect of gene flow on allele frequencies. characteristics of adaptive vs. non-adaptive mechanisms affecting allele frequency. how various evolutionary forces reinforce or oppose one another. Why do population evolve? > natural selection but its not the only thing that cause population to evolve *how is this force likely to affect allele freq in a population *how is this force likely to affect the total amount of genetic variation in a population. (the total standing of genetic variation in a population) 3 modes of selection on the quantitative traits: 1.stabilizing the most wide spread of selection. 2. Directional selection (one extreme is favored over everyone else) (eg. Fast runner cheetah over slow runner) why is there still genetic variation then when it comes to directional variation? Because the environment changes. Selection presuure are not always uniform, it can vary over time. So both alleles are maintained because selection pressure varies temporarily. Selection pressure also vary in a special manner. Environments are not uniform. One range changes from the other range. Selection is the only force that results in adaptations. Adaptation is any trait that increases the fitness of the individual relative to the other individual in the population. So adaptations are relative (involve differences in relative fitness) and environment specific. Adaptations are specific to a particular environment The final type of selection is disruptive. This is the opposite of stabilizing selection. (the individual with intermediate phenotypes/ average having the highest fitness) In disruptive selection, the indivisuals in either extreme are favoured. There isn‟t a shift in population mean value, but there is discontuity arising. Selection pushes the population towards two separate peaks in population. In frequency dependent selection, the fitness of a particular phenotype or a genotypes is gna depend on relative frequency of the population. -ve frequency selection > advantage of being rare (eg. Predators/ prey) over a long period of times > -ve frequency selection will result in both alleles in a population to be maintained. (balanced) the selective advantage will make them more common in a population and it will no longer have the “rare” advantage (eg. rare male mating advantage) the opposite ( not as wide spread) is +ve frequency dependence selection. Selective adv to the most common phenotype in the population. ( usually due predator‟s prior experience) the adv to the common form will cause the more common allele to replace the other allele in the population Selection results in adaptation in populations but it never results in perfection in the environment: trade off> trait may be beneficial in one context but harmful in another context. There will always be compromising between competing demands. Its constraited by the available genetic variation. Selection constrainted by the doiminance relationship of alleles Environment is always changing Selection is the only ADAPTIVE evolutionary force that drives allele frequency. Other conditions of HWE: (unadaptive evolutionary force) Population size has to be really big for a population to be in HWE. The smaller the population is the more heavily it will be influenced by genetic drift Genetic drift > random unpredictable changes in allele frequency due to sampling error (unlike selection in the term of unpredictable and random) Reduction in population size > bottleneck Genetic drift causes one allele goes to fixation (1) and all the other alleles are lost from the population, low genetic diversity Genetic drift opposes the affect of selection. Depends how strong selection is towards a particular allele and the population size. Small population size drift outways the effect of selection. Vise vera Genetic drift decreases variation within a population. Genetic drift increases variation among populations. Mutation is important primarily because it is the new source of genetic variation. It creates new alleles. Mutation is not random (predictable thru biochemical laws etc. ) but it is not directed towards the needs of the organism in the environment Most mutations have neutral effects on fitness. The ones that do are harmful Mutation works in opposition to selection. But it provides raw material for adaptive material Gene flow (migration) movement of alleles between populations. It can introduce alleles that are new to a population. (mutation is ultimately the original source of genetic variation but gene flow can move existing alleles from on population to another) Gene flow can oppose local selective forces Selection-migration balance, preventing population from adapting to their selective environment. *which have similar effects on genetic variation within a population? * on differences between population? 2 types of mating that is not “random: - inbreeding or inbreeding avoidance - assortative or dissassortative mating why evolution is true types of non-random mating effect of non-random mating on HWE and on evolution characteristics of a scientific theory components of the theory of evolution evidence for "descent with modification" examples of homology and why they support the idea of evolution examples of vestigial traits and why they support the idea of evolution role of fossil record as evidence for evolution one of the conditions for a population in HWE is random mating. But this hardly true. 2 types of mating. Assortative mating (more common) or disassortative mating if heterozygotes only mate with hetro, half will be hetro but quarter will be homo and the other quarter will be homo what happens when a population mates non randomly? > taks the population out of HWE but it doesn‟t cause a change allele frequency so it doesn‟t result in evolution. What do scientists mean by theory? A coherent set of testable hypotheses that attempt to explain facts about the natural world. Darwins theory of evolution is a theory. Makes predictions of the natural world. What is meant by true in science? If there is so much evidence that it would be perverse to deny it Difference between theory and a fact. Theory is alleviated to be considered a fact only after they‟ve been tested in many diff ways and non of those test resulted in the theory to be falsified. A statement that cannot possibly falsified is not a scientific theory. Th
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