IB150 EXAM 3 NOTES PDF

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IB150 Exam 3 Notes...

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20. Understand the intimate relationship between populations and genetic diversity A. Calculate allele frequencies given genotype frequencies or number of individuals with each genotype B. Explain (in your own words) the predictions of the Hardy-Weinberg (HW) Principle. HWP predicts: the genotype and allele frequencies of the next generation from given set of parental allele frequencies HW principle makes 2 fundamental claims: 1. If frequencies of alleles A and a in a population are given by p and q, then the frequencies AA, Aa, and aa will be given by p2, 2pq, and q2, respectively, for generation after generation. allele frequencies: p + q = 1 genotype frequencies: p2 + 2pq + q2 = 1 2. When alleles are merely transmitted via meiosis and random combinations of gametes, their frequencies do not change over time, meaning that no evolution occurs C. List and restate (in your own words) the five assumptions/conditions of the HardyWeinberg principle, and know under which conditions it is OK to make these assumptions, or why you are testing for violations of these assumptions. Assumptions: 1. Random mating - Gametes from gene pool combine at random - Individuals not allowed to choose a mate 2. No natural selection - All members of parental generation survive - They contribute equal numbers of gametes to gene pool, regardless of genotype 3. No genetic drift (random allege frequency change) - Alleles are picked in exact frequencies p and q, rather than by chance - Population is infinitely large 4. No gene flow - No new alleles are added by immigration, lost through emigration - All of alleles in offspring population come from original population’s gene pool 5. No mutation - No new alleles introduced into the gene pool Allele frequency changer (thus processes of evolution): natural selection, genetic drift, gene flow, mutation Genotype frequency changer: nonrandom mating Selection is the only evolutionary force that consistently results in adaptation. Mutation without

selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations. Generation-to-generation change in the allele frequencies in a population is the definition of microevolution.

D. Predict allele and genotype frequencies of rare genetic disorders in a population from phenotypic data alone, ASSUMING that the population is in Hardy-Weinberg Equilibrium, and understand the limitations of your estimates. Use the following steps to determine if the population may be evolving. 1. Determine the total number of alleles in the population. 2. Determine the frequency of each allele in the population. 3. Use the equation for Hardy-Weinberg equilibrium to determine the expected frequency of each genotype. (See Hint 2.) 4. Based on the expected frequency of each genotype, calculate the expected number of individuals with each genotype. 5. Compare the expected number of individuals with each genotype to the actual number of individuals with each genotype. If the expected number of individuals with each genotype differs from the actual number of individuals with each genotype, then the population may be evolving.

E. Calculate the expected frequencies of offspring of particular genotypes or phenotypes expected in the next generation if the population is in Hardy–Weinberg equilibrium given allele or genotype frequencies in the current generation F. Be able to apply the Hardy–Weinberg equation to estimate the frequencies of carriers in a population, assuming alleles of the gene in question is in Hardy–Weinberg Equilibrium G. Understand in what sense the Hardy-Weinberg equation represents the prediction of the null hypothesis of biological evolution. Null hypothesis: specified what should be observed if the hypothesis being tested is not correct; status quo HW principle functions as null hypothesis because: biologists often want to test a hypothesis that nonrandom mating is occuring/evolutionary processes is affecting particular trait in population H. Determine whether or not a population is in Hardy-Weinberg equilibrium using the ChiSquare statistic to compare expected and observed genotype frequencies of a population, and explain the biological implications of either rejecting or failing to reject the null hypothesis based on your results. (O-E)2/E → add all up

21. What causes genotype frequencies not to be in HW equilibrium in a population? A. List the four processes that change allele frequencies and the five that change genotype frequencies in populations through time. Allele frequency changer (thus processes of evolution): natural selection, genetic drift, gene flow, mutation Genotype frequency changer: nonrandom mating, everything above B. Restate (in your own words) what it means for an allele to be fixed in a population or lost from a population. A fixed allele is an allele that is the only variant that exists for that gene in all the population. A lost allele means the allele no longer exists. C. Relate allele fixation to genetic diversity (e.g., what is the effect of fixation on genetic diversity?). Fixation results in lack of genetic diversity D. Identify processes that can cause alleles to be fixed or lost and re-introduced. Genetic drift E. Describe the concept of “random sampling of alleles” in genetic drift making specific reference to the parental gene pool and offspring genotypes. Small samples are often different from the wider populations, and differences in small populations don't get "averaged out" as compared to differences in large populations from generation to generation. Random pairings from the parental gene pool meant that for a small selection, there is a higher chance that the offspring phenotype will be skewed from those of the overall population F. Understand how genetic drift can cause alleles to become more or less common or fixed in populations 1. Genetic drift is random with respect to fitness. The changes in allele frequency that it produces are not adaptive. 2. Over time, genetic drift can lead to the random loss or fixation of alleles. In the computer simulation with a population of 4, it took at most 20 generations for one allele to be fixed or lost. When random loss or fixation occurs, genetic variation in the population declines. G. Predict the relative effects of genetic drift in large vs. small populations and predict

the relative time to allele fixation for large vs. small populations undergoing drift. Genetic drift is most pronounced in small populations. - Allele frequencies change much less in the large population than in the small population. - The smaller the surviving population, the higher the likelihood that genetic drift will result in differences in allele frequencies as well as in loss of alleles - Random fluctuations in allele frequency happen in all populations, but most dramatically in small ones H. Compare and contrast the causes and consequences of the “founder effect” and population bottlenecks. Founder effect - A change in allele frequencies that occurs when a new population is established - Each time a founder event occurs, a founder effect is likely to accompany it, changing allele frequencies through genetic drift Population bottlenecks - Type of genetic drift - When a large population experiences a sudden reduction in size - Can be caused by disease outbreaks; natural catastrophes such as floods, fires, or storms; and human-caused catastrophes such as deforestation → only a few individuals are left to establish the next generation - Genetic bottlenecks: sudden reduction in the diversity of alleles in a population I. Define gene flow and relate it to migration between populations Gene flow: movement of alleles between populations via migration, emigration - Equalizes allele frequencies between the source population and the recipient population → homogenize - Alleles of different genes of immigrant individuals get interspersed in genome of existing population through independent assortment, recombination - Very low amount of gene flow required to keep allelic diversity alive (e.g. 1, 2 individuals in isolated populations) J. Explain how gene flow influences effective population size, allele frequencies, and genetic divergence between populations living in different regions. -

Arrival or departure of alleles can increase, decrease, or have no effect on average fitness, depending on the situation BUT movement of alleles between populations tends to reduce their genetic differences

K. Understand how non-random mating can influence genotype frequencies, and be able to illustrate graphically why non-random mating alone will not change allele frequencies

Non-random mating: - E.g. Assortative mating (sexual selection → natural selection) - Positive: seek out similar genotype - Negative: seek out very different genotype, chosen via phenotypic expression of particular genotype - E.g. Inbreeding L. Predict how inbreeding will change genotype frequencies, and be able to graphically illustrate why non-random mating will not by itself change allele frequencies. Inbreeding - Increases homozygosity, decreases heterozygosity - Does not cause evolution, because, although genotype frequencies change, allele frequencies do not change in the population as a whole - Increases the rate at which natural selection eliminates recessive deleterious alleles from a population=→ exposing rare allele to selection - Consequence → Inbreeding depression: decline in average fitness M. Justify why inbreeding does not cause evolution directly, yet can speed the rate of evolutionary change. (above) N. Justify why ALL natural populations will evolve, making reference to assumptions made under the Hardy-Weinberg Principle. ALL natural populations will evolve because... For reference, here are the 5 conditions required to be in HW equilibrium: Large breeding population Random mating No change in allele frequency due to mutation No immigration/emigration No natural selection #1: some populations are large, some are small. Hardy-Weinberg assumes that an interbreeding population is indefinite because it is not evolving. But, even evolution occurs in large breeding populations because... #2: assortative mating is much more likely than random mating. Individuals usually choose their mates, not just spontaneously breed (ex. female choice and male-male competition) #3: Changes in allele frequency is inevitable. Genetic drift is the result of random changes in allele frequency. Mutations are random and spontaneous that cannot be prevented #4: It is possible to isolate a population, which then leads to speciation, but, sometimes, that is

not the case #5: Environmental pressures WILL favor certain genotypes over the other. 22. How do biotic and abiotic interactions lead to adaptations? A. List the four postulates of natural selection 1. Individuals in population have to vary in traits they possess (e.g. human population and its pre-existing phenotypic variation) 2. Variation in population has to be heritable (due to alleles) → genetic - Natural selection doesn’t create alleles; can only work if variation is already present, all it does is pick out certain traits 3. Differential survival → reproduction - Not all animals live up to reproductive age - Even those who do, differ in no. of offspring produced 4. Differential survival has to be due to specific traits → and they have to be the traits that vary in population B. Discuss the consequences of differential survival and reproduction for variation in a population. (Why is “Survival of the fittest” not capturing the whole story?) You have to be able to survive to produce offspring You have to be able to acquire a mate and mate with that organism Fitness The reproductive success of an individual with respect to other individuals in the same population While it is beneficial to be strong, fast, and healthy in order to survive for the longest amount of time, what really matters is one's ability to reproduce. A person with more offspring will have a higher fitness than that of someone with no offspring. C. Compare and relate the roles of reproduction and survival in natural selection. Natural selection is the process by which traits that confer higher reproductive success in a particular environmental setting become more common in the next generation If an offspring receives a trait that is environmentally favorable, they are more likely to survive and reproduce in that same environment than an organism who did not receive said trait. D. Identify sexual selection as a sub-category of natural selection that increases reproductive success through mate acquisition. Sexual selection: ability to attract, acquire mate - female choice - traits that may lower survival rate, but increases the chances of attracting a mate, can be evolved by natural selection

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male-male competition - males compete for opportunity to mate (pattern, process)

E. Define fitness in the context of natural selection. “fitness” → differential reproductive success (due to intraspecific competition or reproductive success) F. Identify that evolution by natural selection results directly from intraspecific competition between individuals of different genotypes. Intraspecific competition: within the species there is competition. Cheetahs: faster ones will survive more because they can get more food than the slower ones G. Characterize how the biotic interactions of interspecific competition and predation and abiotic factors of an organism's environment result in selection pressures from that interaction can that affect intraspecific competition of individuals of different genotypes. -

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They are important because they are what’s causing the fitness differences between the traits. Interspecific- between species. All of these factors cause selection pressures, predation, desert hot dry. All of these cause intraspecific competition because they are the ones that are going to be selected for in the population. One allele makes you faster, selection pressure is competition between cheetahs, fast ones get to eat.

H. Explain why natural selection does not result in evolution of a trait because a population “needed it”, but can only operate on pre-existing variation in the population. Mutations themselves are random, and natural selection does not cause them. Natural selection operates where there is variation in a population. There is no natural selection simply because an environment needed it, it occurs when there is variation that is favorable over other sorts of variation. I. Defend the statement that selection is reactive, and not a directed process with foresight. - Natural selection only works on the immediate, with individuals sexually selecting for and natural selection favoring individuals with certain phenotypes, without regard to possible future events. E.g. in times of drought, a drought-resistant strain of a plant may become dominant, without regards to the possibility of rainy times coming. J. Justify why traits/behaviors for the "good of the species" (but at the cost of an individual's fitness) would not be favored by natural selection.

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"survival of the fittest" takes precedence over all Natural selection favors traits that allow for greater differential reproductive success in a population, and this comes at the cost of traits that could benefit the species

23. How does natural selection cause non-random changes in allele frequencies in a population? A. Discuss the causes of heritable variation and the consequences of differential survival and reproduction for variation in a population. -

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Heritable variation allows for possibly beneficial, negative, or even neutral mutations to get filtered during each generation by natural selection--weeding out negative mutations, passing on positive and neutral ones. Without heritable variation, species would quickly fall victim to parasites who take advantage of identical genetic material in a population and evolution would not occur.

B. Justify why mutation is a random process to introduce alleles, but evolution by natural selection is a nonrandom process that can alter allele frequencies in a population. Mutation happens spontaneously, but evolution is based off phenotype; a healthier phenotype that contributes to survival and higher fitness would be selected for. C. Compare and contrast expected changes in allele frequency in a population depending on if that allele is under selection vs. experiencing drift. Selection: based on the phenotype's effect on the organism's fitness/survival; This is not random Drift: completely random and due to chance D. Compare and contrast different modes of natural selection and relate them to differences in fitness of phenotypes and resulting changes in allele frequencies: (Directional, Stabilizing, Disruptive Selection) -

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Directional - an increase in a type of phenotype is always beneficial - Not found too often in populations - Happens in smaller populations before stopping Stabilizing - an increase in a type of phenotype is only beneficial for a certain amount (ex: beak size) but any bigger/"better" will lead to a lower fitness and so it goes back down - happens with bigger populations. Disruptive - Individuals of extreme phenotypes are favored, and any intermediate phenotypes

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are selected against U-shaped curve

E. Explain multiple ways in which a deleterious allele can persist in a population. -

the carrier does not show deleterious mutations so the carrier still survives the carrier can then pass the mutation down to the offspring which allows for the mutation to be maintained for long periods of time in a population almost impossible to eliminate recessive (deleterious) alleles from a population, since they can remain hidden in heterozygous individuals something really detrimental must occur to the heterozygous state in order to fully eliminate all heterozygotes (and hence any traces of the gene), which is very rare. Inbreeding also allows deleterious alleles to persists in a population

24. How do new species arise? A. Define a biological species Populations of interbreeding organisms, reproductively isolated from other such groups B. Define reproductive isolation and relate it to gene flow among populations Reproductive Isolation: when members of different populations are unable to mate and reproduce successfully Isolation occurs when a population has separated long enough, with the absence of gene flow, so that the original population has diverged to the point where descendents cannot reproduce successfully C. Explain why gene flow makes speciation by reproductive isolation less likely If a population were to split into two, but each new population still interacts with each other, it is less likely for those populations to truly speciate since they are not reproductively isolated (the defining characteristic of speciation) D. Compare and contrast forms of pre-zygotic and post-zygotic reproductive isolation and be able to give examples of each. Prezygotic isolation - prevents individuals of different species from conceiving an offspring successfully - Habitat (Wrong Place) - Temporal (Wrong Time) - Behavioral (Wrong Pick up line) - Mechanical (Doesn't fit) - Gametic Barrier (Gametes can't combine)

Postzygotic Isolation - zygotes (offspring) form, but do not either survive or else have low fitness - Hybrid Inviability: offspring has low fitness - Hybrid Infertility: infertile offspring E. Contrast allopatric and sympatric speciation. Allopatric Speciation - species that live in different geographic areas (mating is impossible) Parapatry Isolation: Populations that live in adjoining geographic areas (mating is possible in overlapping areas) Sympatric Speciation - populations that live in the same geographic area (live in same area, but do not mate) F. Define the concept of “divergence” with respect to two recently isolated populations Dispersal Geographic barrier between populations was already there Vicariance Geographic barrier splits a population that was already there Island-Ma...