Evolutionary Processes and Genetic Variation, Exams of Biology

Download Evolutionary Processes and Genetic Variation and more Exams Biology in PDF only on Docsity! Biology 171 Exam 2 Learning Objectives Latest Questions with Correct 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 sex. 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 4.The population must be large<--prevents genetic drift 5.Individuals must mate at random.<---non-random mating effects allele frequency, no sexual selection or inbreeding Predict genotype frequencies from allele frequencies (and vice versa) for a population in HWE. - Correct answer Allele frequencies and genotype frequencies will remain constant in succeeding generations. Explain how and why HWE is used as a "baseline" for detecting evidence of evolution. - Correct answer If we find a population whose allele or genotype frequencies are not in Hardy-Weinberg equilibrium, we can infer that evolution has occurred. We can then consider, for the gene under study, whether the population is subject to selection, migration, mutation (unlikely because of its rarity), genetic drift, or non-random mating. These are the primary mechanisms of evolution. The Hardy-Weinberg equilibrium gives us a baseline from which to explore the evolutionary processes affecting populations Explain how each evolutionary process(selection, mutation, genetic drift, gene flow)affects levels of genetic variation within a population. - Correct answer Selection: increases variation for most fit traits Mutation: randomly changes genetic variation Genetic drift: genetic variation changes due to chance events Gene flow: can increase or decrease genetic variation depending on direction of flow/migration Define inbreeding and explain how it affects levels of genetic variation within a population. - Correct answer A selective breeding method in which two individuals with identical or similar sets of alleles is crossed. Over several generations inbreeding will increase proportion of homozygous offspring. Doesn't cause evolution since allele frequencies don't change Explain why the species is considered the fundamental evolutionary unit. - Correct answer The species, as an evolutionary unit, must by definition be fluid and capable of changing, giving rise through evolution to new species<--species are not fixed List (and describe) the three key steps in the speciation process. - Correct answer 1. an initial barrier to gene flow emerges 2. genetic makeup of each population changes through selection, genetic drift, and/or mutation 3. reproductive isolating mechanisms evolve Describe the key feature that defines two groups as different species using the biological species concept. - Correct answer species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other organisms 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 when and why the oxygen catastrophe mass extinction occurred, and what kinds of organisms were affected. - Correct answer ?? Describe the likely cause of the End-Cretaceous mass extinction and the evidence that supports that cause. - Correct answer -75% of all species alive went extinct -all non-avian (ornithischian) dinosaurs went extinct, but avian (saurischian) dinosaurs gave rise to birds -adaptive radiation of mammals and crocodiles Cause: asteroid impact 65.5 MYAEvidence: impact crater discovered in 1990s in Gulf of Mexico area thin layer of clay found on our earth is high in element iridium and is abundant in asteroids/meteors but very rare on Earth, so it's an anomaly to have it on Earth.asteroid struck sulfur-rich rock, which acidified the oceans Provide evidence that birds are dinosaurs, including their shared, derived traits. - Correct answer -birds share MRCA with tetrapod dinosaurs (sister taxa) -birds arise from saurischian (lizard-hipped) dinosaurs, not ornithischian (bird-hipped) -morphological bone structures-embryological evidence: knocked out genes that evolved later in a chicken and snout-like structure (like a crocodile) resulted -palate bones changed-shared derived traits for all therapies: hollow pneumatic bones (connect to the respiratory system), S-shaped neck, pterodactyl foot (3 forward facing toe bones and one backward facing), digitigrade posture (stood and walked on its toes), facula (wish bones/collar bones) -shared derived traits for all therapies: all above, keeled sternum, semi lunate carpal -rootlessness is just birds Trace the taxonomic hierarchy of modern humans back to Domain Eukaryote. - Correct answer Australopithecus sepia, homo erectus, homo nailed, homo sapiens (gibbon, orangutan, gorilla, human + bonobo and chimp) + Neanderthals and denisovans Describe the evidence supporting the phylogenetic hypothesis that humans and chimpanzees are more closely related than humans and gorillas. - Correct answer share a MRCA that is more recent and shared derived trait of delayed puberty Draw a phylogenetic tree showing the relationships among modern humans (Homo sapiens), Denisovans, Neanderthals(Homo neanderthalensis),Australopithecus, orangutan, chimpanzee, bonobo, gorilla, and gibbons. - Correct answer Describe the shared derived traits of animals, vertebrates, mammals, primates, and great apes. - Correct answer animals: multicellular eukaryotes without a cell wall; gastrula stage during development; collagen protein vertebrates: cranium and vertebrae mammals: mammary glands, hair primates: eyes on the front of the face (3D vision), 5 grasping fingers on all 4 limbs, flattened nails instead of claws on the fingers and toes great apes: no tail Explain the difference between Family Homicide, Subfamily Hominine, and Tribe Hominine and know the shared derived trait that defines Tribe Hominine. - Correct answer Family Homicide: includes orangutans, gorillas, bonobos, chimpanzees, and human; shared derived trait is robust canine teeth Subfamily Hominine: includes gorillas, bonobos, chimpanzees, and human; shared derived trait is earlobes Tribe Hominine: bipedal African great apes Describe the evidence that there were multiple bipedal lineages of organisms in Tribe Hominine alive at the same time in Earth's history, as well as the evidence that there were multiple species of human (Homo) that coexisted on Earth; in both cases you should be able to give the approximate date for when they coexisted. - Correct answer Until about 200,000 years ago about 6 species of homo coexisted on Earth. Explain how we can infer whether a fossil organism in Tribe Hominine was bipedal. - Correct answer Skull- directly on top of the vertebral column since foramen magnum moved forward Pelvis: Upright posture longer legs under the whole body. Femur angled more Feet- Narrower foot, heel, and big toe (not grasping) Describe the genera Australopithecus and Homo, the relative order of their appearance in the fossil record, their relative ages, and the general features that distinguish the two genera. - Correct answer Australopithecus: -4 to 2 MYA -long arms and curved fingers adapted to climbing -small brain-small body with prominent ape like jaw -big teeth -fully bipedal Homo:-"Humans" (2 MYA) -fully bipedal; large brain; larger body, less prominent jaw -features that allow for manipulating objects, long distance terrestrial movement, teeth that allow for chewing a nutrient dense diet Give evidence for how Homo nailed has changed our views of human evolution - Correct answer Has a mix of primitive and modern features. It has a smaller brain than expected but showed complex behaviors Identify the continent on which Homo sapiens(modern humans) evolved and the accepted date of when they first appeared. Explain how new fossils are suggesting an 2older origin for modern humans. Describe the most recent spread of H. sapiens from Africa to the rest of the world and the general pattern of migration. - Correct answer Africa>Asia>Europe>North America and Australia>South America and Madagascar Explain how researchers know that introgression occurred betweenHomo sapiens, Neanderthals, and Denisovans, and what effects introgression has had on modern human genomes. - Correct answer the transfer of genetic information from one species to another as a result of hybridization between them and repeated backcrossing. (1-4% of non-African H. sapiens genome is derived from Neanderthals) 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 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. Give the timing of when plants, fungi, arthropods, and tetrapod have first arrived on land; explain why plants must have colonized land before animals. - Correct answer Fungi first (>500 MYA), plants came next (approx. 475 MYA), animals came last (400 MYA-arthropods/370 MYA- tetrapod’s). Plants supply biomass. Also, before plants colonized land, oxygen levels were low and carbon dioxide levels were high. Nowadays, due to photosynthesis oxygen levels are much higher on land and plants use carbon dioxide when performing photosynthesis. Also animals would need something to eat to survive. Primary producers needed for animals to survive Explain the distinction between obligate versus facultative parasites and describe the ways biologists categorize parasites. - Correct answer Obligate parasites need one or a few types of host in order to thrive, so if they are unable to reach this species their life cycle ends. Facultative parasites can survive in many different host species in order to complete its life cycle. Explain how parasites can change host behavior and influence host population size; also explain their importance in food webs and how they can dominate biomass in ecosystems. - Correct answer Parasites are very common: 50% of species are parasites. Even parasites get parasites, and host-parasite coevolution is very common. Parasites can account for a large part of biomass in food webs. Parasites can alter host behavior because it promotes transmission of the parasite. Explain how the nature of interactions between two species can change(i.e. From commensalism to parasitism)as environmental conditions change(i.e. Under different parasite densities). - Correct answer Mutualisms are dynamic and can become parasitism if environments change Describe the features that distinguish arthropods from other animals, the diversity of arthropods, and some drivers of arthropod diversity. - Correct answer Shared derived traits: exoskeleton (chitin) and jointed appendages Arthropods includes insects, crustaceans, and spiders Cuticle made of protein covering their bodies, providing them with flexible, lightweight protection Most diverse animal group Bilateral symmetry Driver of arthropod diversity: plant-pollinator and plant-herbivore coevolution Give defining characteristics of Hexapods (insects)and explain their importance in mutualistic and consumptive interactions. - Correct answer Shared derived traits: 3 part body: head, thorax (6 legs), and abdomen Biggest herbivore on planet Most abundant arthropod Three key adaptations: desiccation-resistant eggs, wings, and metamorphosis 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 outweighs 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