Evolutionary Processes and Population Genetics, Exams of Biology

Download Evolutionary Processes and Population Genetics and more Exams Biology in PDF only on Docsity! Bio 171 Exam 2 Learning Objectives Final Exam Questions with Answers Explain how directional, stabilizing, and disruptive selection can be applied to sexual selection. - Correct answer Directional: when an extreme phenotype is favored over other phenotypes causing the allele frequency to shift over time to that phenotype. This could happen during intersexual selection, if the females choose the male with the orange spots, and therefore that trait gets passed down. Stabilizing: When the population means stabilizes on a particular non-extreme trait value. When the population measures select against the two extreme sides of the trait, to a more central one. Can happen if the female prefers the median trait as opposed to any other extreme form. Disruptive: When two of the extreme phenotypes are selected for, this can happen if males engage in intersexual selection and males fight off other males because of their extreme phenotypes, are eventually selected for by the females and have a higher chance of passing on these traits. Define sexual selection and describe how it differs from natural selection. - Correct answer Sexual selection: individuals with certain heritable traits are more successful at attracting and keeping mates and therefore, reproduce at a higher rate • Different from other types of selection: female chooses male mate Distinguish between intersexual and intersexual selection. - Correct answer 1. Intersexual selection: focuses on interaction between males and females example: male peacock's colorful tale, evolution driven by female preference 2. Intersexual Selection: Focuses on individual's interactions between one sexes. Traits evolve from competition ex: larger more powerful males win fights-->so develop horns Explain the causes and consequences of stronger sexual selection in males than females. - Correct answer *Males usually compete more intensely for mates than do females and females are choosier than males* 1. Sexually selected traits are more common in males. Males often have exaggerated traits they use in fighting or courtship 2. Causes: An isogamy: gametes of different sizes. Female make fewer larger eggs-- >more invested in process--> choosier with mates; Fundamental asymmetry of sex 3. Consequence: Fitness more variable among males Explain how an isogamy leads to the "fundamental asymmetry of sex" and how this influences male and female mating behaviors. - Correct answer an isogamy is defined as having gametes of different sizes. Males have many, many small gametes, while females have few large gametes. This means that females are choosier about who they mate and males must compete intensely among other males because females are more invested and require more energy for a female to make an egg, since they have fewer eggs to spare and are more protective towards who they use them with. This contributes to the "fundamental asymmetry of sex, which influences evolution of traits. Compare and contrast mutation, migration, genetic drift, natural selection, and sexual selection in terms of their effects on genetic variation and allele frequencies. - Correct answer Mutation: Introduces new alleles into a population; increases the amount of genetic variation within a population/species. They are the primary source of genetic diversity. Genetic drift: Can change allele frequencies by CHANCE alone. Decreases genetic variation because the alleles either become fixed (homozygous) or lost over time. Migration (gene flow): Results in alleles entering and/or leaving a population. Can increase or decrease genetic variation, but makes connected populations have more similar allele frequencies. Natural selection: An increase of selection for specific alleles which aid in survival, selection against deleterious alleles cause a decrease in allele frequency. Can increase genetic diversity (speciation) or decrease genetic diversity (extinction) Explain how natural and sexual selection can cause fitness trade-offs. - Correct answer if there are camouflaged males favored by predator avoidance (natural selection), and brightly colored/patterned males favored by females (sexual selection), then there is a trade-off between mate attraction and predator avoidance. Give the frequency at which an allele is considered "fixed" within a population and the frequency at which an allele is considered "lost" or "eliminated" from a population. - Correct answer Fixed: allele frequency is 1 (since 1 means 100% of the population is homozygous for the particular trait) Lost: allele frequency is 0 Define mutation, gene flow (resulting from migration), and genetic drift, and explain how genetic drift and gene flow differ from one another. - Correct answer Mutation: a random error in gene replication that leads to a change and generates new alleles Gene flow: The movement of alleles from one population to another through interbreeding of some of their respective members. Genetic drift: A change in the allele frequency of a population as a result of chance events rather than natural selection. Calculate allele frequencies of a population. - Correct answer number of copies of a given allele/total number of alleles of gene Contrast the impact of genetic drift on genetic variation in large and small populations. - Correct answer More of an effect on small populations Give an example of species affected by a founder effect and a population bottleneck. - Correct answer Species effected by founder effect: Wolves from Canada cross an ice bridge in 1949 and establish a population on Isle Royale (founder effect) Describe at least two situations where the biological species concept cannot be used to define species. - Correct answer cannot be applied to asexual or fossil species Compare and contrast the biological species concept, the morph species concept, and the phylogenetic species concept. - Correct answer Biological: species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups Morph species: The idea that members of the same species usually look like each other more than like other species. Phylogenetic: The idea that members of a species all share a common ancestry and a common fate. (Species are defined by unique genetic history) Identify the difference between prezygotic and post zygotic isolating factors. - Correct answer Pre- Describes factors that prevent the mating or fertilization of an egg. No hybrid zygotes formed Post- Describes factors that cause the failure of the fertilized egg to develop into a fertile individual. Define and recognize the following types of prezygotic isolating barriers: behavioral, temporal, ecological, mechanical, and game tic isolation. - Correct answer Behavioral: Describes individuals that only mate with other individuals on the basis of specific courtship rituals, songs, and other behaviors Temporal: Pre-zygotic isolation between individuals that is reproductively active at different times. Ecological: Pre-zygotic isolation between individuals that specialize ecologically in different ways. Species live in the same area but use different habitats so rarely encounter each other Mechanical: Morphological (anatomical) differences prevent fertilization.Gametic: Incompatibility between the gametes of two different species. Define and recognize the following types of post zygotic isolating barriers: hybrid in viability and hybrid sterility. - Correct answer Hybrid in viability: A post zygotic barrier in which hybrid zygotes fail to develop or to reach sexual maturity Hybrid sterility: A post zygotic barrier in which hybrids fail to produce functional gametes (hybrids can't reproduce) Compare and contrast allopatric and sympatric speciation - Correct answer Allopatric: The formation of new species in populations that are geographically isolated from one another. Most common mode of speciation in animals Sympatric: The formation of new species in populations that live in the same geographic area. Speciation without geographic separation-Initial barrier to gene flow is biological (genetic, ecological, or behavioral) Explain how autopolyploid, natural selection, and sexual selection can lead to sympatric speciation. - Correct answer Autopolyploid: errors during meiosis = extra sets of chromosomes in gametes and offspring (3n or 4 n mutants are unable to breed with normal 2n individuals in population; they are "new species") Natural/sexual: ecological or behavioral factors Explain the roles that selection, genetic drift, gene flow and mutation may play in speciation. - Correct answer a barrier to gene flow begins the process. Then, genetic makeup changes through selection, genetic drift, and/or mutation. Finally, reproductive isolating mechanisms evolve Give examples of traits in Anoles lizards that are expected to be affected by natural selection and/or sexual selection. - Correct answer Short legs vs. long legs for difference habitats (natural selection) Dewlap color (sexual selection) Describe how the diverse species of anoles lizards found in the Caribbean evolved. - Correct answer those with long legs can run up and down tree trunks while those with short legs live on small twigs Describe the conditions that favor adaptive radiations. - Correct answer 1) a single ancestral species rapidly diversifies into many descendent species 2) The descendant species diverge into genetically different forms that occupy distinct habitats Explain what the "Cambrian explosion" represents, when it occurred, and how it is an example of an adaptive radiation. - Correct answer the rapid diversification of multicellular animal life around the beginning of the Cambrian Period, resulting in the appearance of almost all modern animal phyla. Explain how fossils form and the limitations of the fossil record; describe the two main types of fossils. - Correct answer most form when an organism is quickly buried in sediments before decomposition occurs. Limitations: habitat bias, taxonomic bias, temporal bias, abundance bias 2 main types of fossils: body fossils: show us what the organism looked like; includes fossilized bones, shells, organisms preserved in other ways like ice, amber, petrified wood, or pollen trace fossils: footprints, coprolites (fossilized poop), burrows, tracks; indirect evidence of behavior Explain how paleontologists and geologists can estimate dates of important events in Earth's geological history using radioactive decay of different isotopes(such as 14C and 238U); be able to apply these principles to understand the age of a fossil if given information on radioisotopes and their decay rates. - Correct answer Archaeologists commonly uses the radioactive decay of the isotope carbon-14, or 14C, to date wood and bone. After death, the unstable 14C in these materials begins to break down, losing an electron to form 14N, a stable isotope of nitrogen. Laboratory measurements indicate that half of the 14C in a given sample will decay to nitrogen in 5730 years, a period called its half-life (Fig. 23.17). Armed with this information, scientists can measure the amount of 14C in an archaeological sample and, by comparing it to the amount of 14C in a sample of known age—annual rings in trees, for example, or yearly growth coral skeletons—determine the age of the sample. Describe the main events that occurred in the Hadean, Achaean, Proterozoic and Phanerozoic eons. - Correct answer Hadean(4-5-4 BYA): Formation of Earth Arcana(4-2.5 BYA): First evidence of life, photosynthesis Proterozoic(2.5-540 MYA): first evidence of an oxygen-rich environment, first eukaryotic microfossils, major diversification of eukaryotic microorganisms, first animal fossils Phanerozoic(540-present): colonization of land and fungi by plants, arthropods, tetrapod’s, K-T Describe the relative order and approximate timing of the following events: formation of Earth, first molecular & fossil evidence of cells, evolution of photosynthesis, development of oxygen-rich environments, first eukaryotic cells, first animals, Cambrian explosion, colonization of land by plants and fungi, colonization of land first by arthropods then vertebrates, End-Cretaceous extinction, diversification of birds & mammals. - Correct answer 1.formation of Earth (4.5 BYA, Hadean Eon), 2. First evidence of prokaryotic cells (~3.5 BYA, Arcana Eon), 3. Evolution of photosynthesis (3.5 BYA, Arcana Eon), 4. Development of oxygen-rich environments (2.4 BYA, Proterozoic Eon), 5. First eukaryotic cells (~1.8 BYA, Proterozoic Eon), 6. First animals (600 MYA, Proterozoic Eon), 7. Cambrian explosion (540 MYA, Phanerozoic Eon), 8. Colonization of land by plants (475 MYA, Paleozoic Era), 9. Colonization of land first by arthropods (420 MYA, Paleozoic Era) 10. And then tetrapod’s (365 MYA, Paleozoic Era), 11. First flowering plants (~125 MYA, Mesozoic Era), 12. First primates (~65 MYA, Cenozoic Era), 13. First hominines (~7 to 5 MYA, Cenozoic Era), 14. First Homo sapiens (Cenozoic Era, Neocene Period, 200,000 years ago) Explain how mass extinctions differ from background extinctions and how they provide opportunities for adaptive radiations to occur. - Correct answer Adaptive radiations occur when a single ancestral species rapidly diversifies into a large number of descendant species; these descendants are genetically diverse and have different morphologies that occupy distinct habitats. Adaptive radiations are a major pattern in the history of life and occur when new ecological opportunities arise and/or when new morphological innovations arise. In the fossil record, we often see adaptive radiations following mass extinction events because they provide new ecological opportunities, after resources become available. Describe when and why the oxygen catastrophe mass extinction occurred, and what kinds of organisms were affected. - Correct answer ?? Explain how genetic variation is distributed within and among human populations today and how these patterns in genetic variation are driven by patterns of migration. - Correct answer -human populations are not biologically distinct groups (most physical variation ~94% is within racial groups) -there is more variation within "racial" groups than between them -trait variation among humans is continuous (most traits are continuous, not discrete) -because traits are inherited independently, there's no reason to think that physical traits like skin color or hair texture correlate with any other trait Give evidence about the nature of variation in traits such as skin color and height, including whether it is continuous or discrete and the role of the environment. - Correct answer Continuous traits since most human variation is gradient. Environment plays a major role (ex: average height has increased over the years) Explain why what we know about trait variation and genetic variation within racial groups supports the statement that "physical variations in the human species have no meaning except the social ones that humans put on them". - Correct answer there is more variation within "racial" groups than between them Use information about the requirements for natural selection to interpret evidence and scenarios related to evolution in modern humans - Correct answer Look at: -changes in allele frequency -DNA sequence data from specific genes -genome wide association studies using SNP's to detect selection Describe how birth, death, immigration, and emigration influence population growth rate and population size, and how absolute numbers of births, deaths, immigrants, and emigrants relate to birth, death, immigration, and emigration rates, respectively. - Correct answer Birth and immigration rates increase population size/rate Death and emigration rates decrease population size/rate Growth rate = (B + I) - (D + E) B = number of births (b) between times 0 and 1 (same applies for all vital rates) Define the geometric rate of increase, λ, and per capita growth rate, r, and describe how they can be used to understand how populations change over time. (NOTE: there are errors in the formulas in your textbook! Use the formulas from your lecture notes.) - Correct answer λ expresses a population's growth rate over a discrete interval of time (ex. 1 year) more useful for animals that breed at a certain time (mating season)r expresses the instantaneous per capita growth rate. More useful for animals that breed continuously (humans) Explain the relationship between lambda (λ)and r. - Correct answer λ = ear r = line r>0 and λ>1, increasing r=0 and λ=1 stable r<0 and λ<1 decreasing Apply the geometric (discrete), exponential, and logistic growth equations to predict population growth rate and population size in the future.(Note: we will give you equations on the exam, but you will have to recognize which is which and know how to apply them.) - Correct answer exponential: r doesn't change, density-independent logistic: r changes, density-dependent Recognize that population growth rate is constant under exponential growth, but that population growth rate slows as population size increases under logistic growth. - Correct answer Explain why populations do not grow exponentially forever. - Correct answer Populations doesn’t grow exponentially forever due to resource limitation. Possible limitations: food, space, nutrients, nesting sites, etc. (density-dependent factors) Identify exponential vs. logistic growth curves. - Correct answer Exponential grows forever, logistic starts exponential but stabilizes at carrying capacity (K) Explain the factors that influence the per capita growth rate(r)of populations undergoing logistic growth. - Correct answer abiotic factors: density-independent, natural disasters Biotic factors: density-dependent: predation, competition, parasitism, pathogens, mutualism doesn't regulate population Compare and contrast density-dependent and density-independent factors, recognize a factor as density-dependent or density-independent, and analyze a graph to determine if a density-dependent or density-independent factor is influencing population growth. - Correct answer DD: at low densities, resources like food do not limit growth as much but at higher densities, they exert more influence on population growth, spurring competition for available resources. Examples: food, space, nutrients, nesting sites, disease DID: Influence population size without regard for population's density. Example: severe drought, prolonged cold period, or other natural disasters. Define population regulation and summarize the factors that regulate population growth. - Correct answer both biotic and abiotic factors influence population size. Biotic factors include predation, competition, parasitism, mutualism, and disease, while abiotic factors include temperature, disturbance, precipitation, pollution, etc. Only biotic factors can "regulate" a population, and, of the biotic factors, only those that add a negative feedback (NOT mutualism). Compare and contrast herbivore, predation, and parasitism; also be able to compare these with mutualism, competition, commensalism and symbiosis (see next lecture), and understand what the general term "enemy-victim" means. - Correct answer Herbivore: +/-; consumption of plant tissues by an animal (herbivore); herbivores sometimes eat whole plant, but usually only consume a portion Predation: +/-; consumption of most or all of another individual by a predator; fatal to prey Parasitism: +/-; partially consume another individual, the host; differ from predators be typically much smaller than host, live on or in a single host individual for a long time, and parasitism is not necessarily fatal to the host Mutualism: +/+ Competition: -/- Commensalism: +/0 Enemy-victim: also defined as consumptive. Compare and contrast inducible and constitutive defenses; apply your knowledge of these defenses to specific examples, using that knowledge to determine whether a defense is inducible or constitutive. - Correct answer Constitutive: always present a relatively constant level Inducible: synthesized or mobilized to a site upon injury from a natural enemy; either produced only when an organism is exposed to its natural enemy or produced in greater amounts when exposed to natural enemy Costs associated with both Explain how plant defenses can be co-opted by their herbivores. - Correct answer Herbivore influences plant population size, individual growth rate, plant evolution (constitutive and inducible defenses), and plant community structure (number of species present and abundance of each species) For example, the monarch butterfly feeds off of milkweed. Milkweed produce toxins and a quick setting glue. Monarch butterflies have evolved to be able to feed on milkweed despite their defenses. They also "steal" the plant's defenses are use them to defend themselves. Describe how predators and parasites can regulate prey/host population sizes. - Correct answer in the hare-lynx populations, predators drive the hare population cycles. A experiment was taken where hares were put in a plot with an electric fence (predator exclusion), extra food, and predator exclusion/extra food. The hare population was significantly higher in the plot with predator exclusion/extra food than it was in the food added and predator exclusion plot. Thus, food and predators drive the hare population. Explain how predators can change prey behavior and influence all vital rates, and how they can exert strong selection on prey. - Correct answer Increase emigration: prey leave habitats where predators are present Decrease immigration: prey do not immigrate into areas where predators are present Increase births: prey eat less when predators are around Decrease deaths: kill prey Prey under strong selection to avoid being eaten by predators. competition. - Correct answer if one species has a higher fitness than the other, eventually, they will drive the other out Co-occurring: character displacement (evolutionary change in species traits which allows co-occurring species to use different resources) and resource partitioning (evolutionary change in resource use by coexisting species) Describe and explain the setup, results and conclusions of Connell's field experiment on competition between two barnacle species. - Correct answer transplanted rocks containing different kinds of barnacles do different levels of competition - found that S competitively excludes CH Explain how mutualism increases organismal growth rates, survival, and fitness and/or population growth rates for both species involved. - Correct answer +/+: fitness increases for both species Explain how mutualisms between mycorrhizal fungi and land plants work and how the interaction improves fitness for both the fungal species and the plant species. - Correct answer Mycorrhizal fungi live in the plant roots and hip plants take up essential nutrients from the soil. Plants supply the mycorrhizal fungi with carbs in the form of sugars and provide them with sugar. Explain how mutualisms between Rhizobium bacteria and legumes work and how the interaction improves fitness for both the bacteria and the plant species. Be able to compare and contrast mycorrhizal fungi-plant and Rhizobium bacteria-legume mutualisms. - Correct answer Rhizobium bacteria live in nodules on plant roots. These bacteria can fix nitrogen (take it from the atmosphere as N2 and convert it into nitrate and ammonium). This gives plants with rhizobium a big advantage as nitrogen is often limiting in terrestrial ecosystems. In return, the bacteria get sugars and a "home" in the roots of the plants. Describe some of the organisms that can fix nitrogen. - Correct answer Rhizobia, some other bacteria and archaic, trichodesmium (sea straw) Describe the basics of plant reproduction and explain how plants and pollinators are adapted to each other as part of plant-pollinator mutualisms. - Correct answer Pollination: movement of pollen grasses from 1 flower to the stigma of another flower (of the same species) Wind or pollinators Fertilization: sperm fertilizes egg and plant embryo forms (seed) Explain how mutualisms between angiosperms and pollinators work and how the interaction improves fitness for both interacting species. - Correct answer the flower producing a nectar reward uses up valuable sugars; however, its fitness is greatly increased with attracting pollinators with nectar, and the benefits outweigh the costs. Explain how the nature of interactions between two interacting species can change(based on comparison of costs and benefits)as environmental conditions change(i.e., as density of one of the species changes). - Correct answer Mutualisms are dynamic and can become parasitism if environments change Describe how mutualisms are vulnerable to cheating, and be able to give an example of cheating in an actual mutualism. Characterize the relationships between ants, Acacia, and phloem-feeding insects. - Correct answer ex. orchids- 50% practice deceit pollination (don't reward pollinator with nectar) Ex. cheating ants: usually ant plants receive protection from herbivores in exchange for giving ants nectar, but some ants raise insects like cattle, and these insects can be negative for the ant plant Given data regarding two interacting species, be able to identify the interaction as competition, commensalism, mutualism, parasitism, or predation (or as one in which there is not sufficient information to determine the type of interaction) - Correct answer competition: -/- , A grass and a wildflower: each species loses the water, nutrients, and access to sunlight that the other takes Commensalism: +/0, Egrets and cattle: Egrets benefit from insects stirred up by cattle; cattle are unaffected by egrets Mutualism: +/+, Flowers and bees: flowers gain pollination; bees gain nectar and some pollen Parasitism: -/+, Tapeworms and humans: tapeworms benefit from absorbing nutrients in human intestine; humans lose nutrients Predation: -/+, Arctic foxes and lemmings: foxes benefit from eating lemmings; lemmings lost opportunities to reproduce Explain the evidence for the theory of endosymbiosis, which explains the origin of chloroplasts and mitochondria in eukaryotes - Correct answer Mitochondria and chloroplasts are the same size as alpha-Proteobacteria and cyanobacteria, respectively. Mitochondria and chloroplasts contain their own genome located in a circular DNA molecule, just as alpha-Proteobacteria and cyanobacteria do. Mitochondria and chloroplasts also divide by binary fission like bacteria do. Mitochondria and chloroplasts also have 2 or more membranes, which is consistent with an engulfing mechanism. Most convincing: When biologists sequenced the genomes of mitochondria and chloroplasts, the molecular phylogenies clearly showed that the DNA from mitochondria nested with the alpha-Proteobacteria group and the DNA from chloroplasts nested with the cyanobacteria group. Explain what the arrows represent in food chains and food webs and why the arrows go from the organism being consumed to the consumer - Correct answer Arrows represent the flow of energy through the food web, so they should go from the organism being eaten to the organism eating it Define how ecologists use the term "omnivory"and be able to identify primary producers, primary consumers, secondary consumers, and omnivores in any food web - Correct answer broader sense of the word: organism that feeds on two or more trophic levels. Ex. a tertiary consumer that feeds on both primary consumers and secondary consumers Explain what trophic pyramids represent - Correct answer These diagrams have a pyramidal shape because the biomass of primary producers generally much larger than the biomass of primary consumers, and the biomass of primary consumers is, in turn, much greater than that of secondary consumers, and so on. The reason for this is that energy transfer from level to level is inefficient. Because of wastes, work, and heat dissipation, only about 10% to 15% of the energy available in biomass at one level gets incorporated into biomass at the next level. Like food webs, trophic pyramids relate community structure to the fundamental biological processes at work in the carbon cycle. Explain how interactions among species can generate indirect effects - Correct answer trophic cascade Distinguish among keystone species, dominant species, and ecosystem engineers - Correct answer Keystone: have an effect on communities that is disproportionate to their abundance or biomass Dominant: very common, so as a result, have a large effect on the community composition ex. maple trees are dominant and have a large effect, but aren't keystone Ecosystem engineer: organism that creates, maintains, or destroys, or in some other way substantially alters a habitat. Ex: beavers create dams Explain how keystone species impact community structure and composition - Correct answer have large indirect effects on communities (do not interact directly but through the chains of species) ex: arctic foxes have an indirect positive effect on grass be direct negative effect on geese and lemmings, which consume grass Explain how trophic cascades can affect community composition - Correct answer when a top predator influences the density of species at all trophic levels below it Can influence energy flow at multiple trophic levels as well as population sizes of many trophic levels and thus can have big impacts on community compositions If omnivore is present, strength of direct AND indirect effects needed to predict the effects on community dynamics Explain how omnivore complicates our ability to make predictions about the effects of consumer removal on food web dynamics - Correct answer Omnivore complicates our ability to make predictions about the effects of consumer removal on food web dynamics because when species start eating other trophic levels then there will be