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BIO 182 EXAM 2 QUESTIONS AND ANSWERS
How many modes of selection are there? 3 What are the modes of selection? Stabilizing selection, directional selection, and disruptive selection Stabilizing Selection The mean of the trait remains similar over time but the standard deviation decreases Directional Selection The mean phenotype shifts in a particular direction Disruptive Selection The standard deviation of the trait increases as individuals with the mean value disappear. Stabilizing Selection Explained The stronger the selective pressure against extreme phenotypes, the narrower the distribution of phenotypes will be in future generations. In the end, the size of the standard deviation will reflect both the strength of selection against extremes and the frequency of mutations creating new variation. Thus, when we observe a wide range of
phenotypes in a population, we might infer weak selective pressure against the extremes. Directional Selection Explained The population's environment changes. The mean phenotype in the population may no longer be the phenotype that reproduces the most. Over time, we should expect the mean phenotype to shift higher or lower, depending on the direction of selective pressure. Once the mean phenotype catches up to the change in the environment, stabilizing selection will resume. The environment must change slowly enough for the population to persist. If the environment changes too quickly, no members of the population will be able to reproduce, leading to extinction. Disruptive Selection Explained A population can occupy an environment in which individuals with extreme phenotypes reproduce more than individuals with the mean phenotype. This mode of selection occurs when several distinct strategies confer greater reproductive success than other strategies do. Can produce new species when individuals choose to mate only with similar-looking individuals. This non-random mating prevents recombination from restoring intermediate phenotypes. Evolution by Natural Selection Heritable variation leads to differential reproductive success Selection and Fitness Directional Selection Equation y=bx+c y=relative fitness x= trait value b= strength of selection c=parameter True or False? If the slope of the relationship between the phenotype and fitness is positive, natural selection would decrease the phenotype over generations. False, it would increase the value of the trait over time Stabilizing Selection Equation
1. A snake with stripes would be more likely to survive by fleeing predators in a straight line. (T/F) True 2. Regardless of escape behavior, the color pattern of snakes will be influenced by directional selection. (T/F) True 3. Over many generations, the population of snakes should evolve toward striped snakes that flee by turning or checkered snakes that flee straight. (T/F) False 4. The strength of selection for a color pattern is greater in snakes that flee by turning than in snakes that flee straight. (T/F) True 5. Although the researcher estimated fitness by survival, he could have also used another proxy for fitness, such as mating success. (T/F) True Asexual Reproduction Directs cells to divide and develop into new tissues and organs. This process takes time and energy, but these resources go directly into the production of offspring. Only organisms that fertilize their own eggs can reproduce sexually without a mate; however, these organisms don't get the benefit of creating genetically diverse offspring. Sexual Reproduction An organism must spend much more time and energy than that required to build an offspring. The additional expense arises because sex requires a mate. Time and energy must be spent to find a suitable partner and convincing that individual to share the genetic benefits of sex. Hermaphrodites Sex can occur between any two individuals in a population, because every individual produces sperm and eggs. Hidden genetic cost of sex
Offspring from sexual reproduction contains only half the alleles of each parent. By contrast, an offspring from asexual reproduction carries a nearly identical set of alleles as its parent does. Therefore, sexual organisms must produce twice as many offspring to receive the same fitness as an asexual organism receives. Fertilization Union of two cells from different organisms Haploid An organism or cell having only one complete set of chromosomes. Diploid Cells containing 2 sets of chromosomes Ploidy level number of sets of chromosomes in a cell homologous chromosomes Nuclei contain two copies of each chromosome in diploid plants and animals. Contain the same genes arranged in an identical order. Diploid Organism Inherits one copy of each homologous chromosome from each parent, which combine to make a genetically unique diploid organism. Gametes Haploid cells, containing a single copy of each homologous chromosome, are found only within structures that give rise to gametes. All animals and most plants produce gametes called eggs and sperm. Meoisis Nuclear division that forms haploid cells The 2 parts of meiosis:
- Meiosis I - a cycle through which a diploid cell divides to create two haploid cells, each receiving one of the homologous chromosomes.
- Meiosis II - a cycle through which the two haploid cells divide to form four haploid cells, which later develop into sperm or eggs. Meiosis Stages
1. If the researchers are correct, the X chromosomes likely cross over at the locus that controls normal or barred eyes. (T/F) True 2. After crossing over, both chromosomes will contain new alleles at the point of crossover. (T/F) True 3. If the chromosomes crossed over equally, the resulting gametes would likely have the same number of genes. (T/F) True 4. An allele at locus A is more likely than an allele at locus B to remain linked to the allele for barred eyes. (T/F) False 5. The allele at locus B is likely to be lethal when combined with the allele for barred eyes. (T/F) False 6. If the X chromosome crosses over with the Y chromosome, the resulting gametes are likely to generate healthy offspring. (T/F) False Genetic Drift Populations evolve randomly. By chance, some individuals have more offspring than others—not from an advantage conferred by alleles, but just because some individuals happened to be in the right place at the right time (e.g., when food was abundant). Or even because other individuals happened to be in the wrong place at the wrong time (e.g., when a predator was hunting). Genetic drift can eliminate an allele from a population. Genetic drift and population size Smaller populations evolve rapidly by genetic drift. Any event that randomly eliminates a large fraction of a population will magnify genetic drift Bottleneck Effect
Loss of genetic diversity following a sudden drop in a population. Founder Effect The loss of alleles that occurs when these individuals start a new, smaller population. stochastic process Random events cause an allele to increase or decrease in frequency. Even an allele that tends to increase or decrease an organism's fitness in a large population can decline because of genetic drift in a small population. Neutral allele One that confers no reproductive advantage or disadvantage Formula for the chance of an allele spreading If only 1 copy of the allele exists in the entire population, making the frequency 1/(2N) where N is the number of diploid individuals. The chance of this allele spreading to the entire population is 1/(2N), so the chance of the allele not spreading is 1 - (1/(2N)). The chance of a beneficial allele not spreading by natural selection Depends on its initial frequency and its fitness benefit. Rare and weakly beneficial alleles are most likely to disappear by genetic drift. At any moment, the frequency of an allele in a population depends on this selection-drift balance. Genetic drift occurs whenever a random event causes a genotype to reproduce more than others in a population. (T/F) True On average, genetic drift will increase the frequency of a deleterious allele. (T/F) False If a population doubles in size, a deleterious allele should become less likely to drift to a higher frequency. (T/F) True Genetic drift cannot occur in the same generation as natural selection. (T/F) False Genetic drift cannot eliminate a beneficial allele from a population. (T/F) False What causes genetic drift?
asexual organisms a species comprises all individuals with similar genomes binary fission a process similar to mitosis in sexual organisms conjugation a process where cells pass DNA through a temporary portal evolutionary species Groups defined by genetic similarity alone sexual organisms a species comprises all individuals that can mate with one another to produce fertile offspring biological species Groups defined by the potential to produce fertile offspring hybrid An animal carrying genes from two species. This hybrid would probably be infertile even if it grows to adulthood. The problem with hybrids arises from different genes whose products conflict during development or preproduction. Thus, even though hybrids occur, the gene pools remain separated because hybrids cannot reproduce. True or False? A herring gull and a black-backed gull are different biological species. False True or False? Two species mate but their offspring die before reaching adulthood. A more efficient way to prevent interbreeding would be to have incompatible genitals. True What isolates species? Pre-zygotic Use different habitats, active at different times, aren't sexually attracted, genitals don't match, and gametes cannot fuse What isolates species? Post-zygotic Hybrids die young and hybrids are sterile Allopatry populations that live in different areas
Sympatry occurs when populations are in the same geographic area When populations become geographically separated for a period and then come back into contact, they __________ become different species. sometimes Which of the following observations provides the best experimental evidence that populations diverge during allopatry? Hybrids of offspring cold-adapted and saline-adapted genotypes were less viable than purebred offspring. Speciation occurs more often between allopatric populations than it does between sympatric populations. (T/F) True The following 5 questions are based on this info: Seven populations of salamanders in the genus Ensatina occur throughout the western edge of the United States (see figure below). For years, these populations were considered separate species, because they look different from each other. However, biologists studying these populations discovered that most of these population interbreed to produce viable and fertile hybrids. The only two populations that cannot interbreed are the ones at the southern edge of the range, referred to as Ensantina klauberi and Ensatina eschscholtzii. Ensantina klauberi and Ensatina eschscholtzii could be considered different morphological species. (T/F) True Ensantina klauberi and Ensatinaesch scholtzii should be considered different biological species. (T/F) False The genes of Ensatina eschscholtzii should be more similar to the genes of Ensatina xanthoptica than they are to the genes of Ensantina klauberi. (T/F) True
True or False? An enzyme maintains a rigid structure while catalyzing a reaction. False Which type of chemical bond will stabilize an enzyme's structure the most? Covalent True or False? The enzymes of animals in old vents should be more flexible than those of animals in young vents. True Phosphoglycerate mutase An enzyme required for glycolysis. Can have different alleles that have mutated and do better at different temperatures. Why don't species evolve wider niches? Ability to perform at optimal temp isn't as good as if you had a more specialized/ narrower niche. You'd have to be a heterozygote to have a wider niche and make twice as many alleles, using more energy. Use this information and your knowledge of biology to answer the following questions: Scientists believe that when a species adapts to high temperatures it loses its ability to function at low temperatures. To test this hypothesis, researchers took populations of bacteria growing for years at 37° C and let them evolve at 42° C for 100 days. The nice thing about bacteria is that you can freeze them today and defrost them years from now and they will start to grow. Therefore, the researchers could freeze some bacteria at the start of their experiment and then compare these genotypes to the ones left at the end of their experiment.
1. To replicate this experiment, researchers only needed one population of bacteria, because bacterial populations contain millions of individuals. False 2. To control for stress, the researchers should have frozen some bacteria at the end of the experiment and defrosted these descendants along with their ancestors before comparing their thermal niches. True 3. If adaptation occurred, genotypes remaining at the end of the experiment should have had more rigid enzymes than their ancestors had. True
4. If adaptation occurred, genotypes remaining at the end of the experiment should outcompete their ancestors at 37°C and at 42°C. False 5. Assuming that the ancestral populations and the evolved populations were compared under the same environmental conditions, any difference in fitness at 42C would more likely resulted from adaptation than plasticity. True Phenotypic plasticity One genotype has multiple phenotypes. Environment triggers change UV light Bad: causes skin cancer. Good: helps make vitamin D Melanin skin pigment that protects against skin cancer in places that get a lot of sun. Not worried about getting enough vitamin D. What can also affect skin color? Certain diets- like fruits and veggies that are rich in carotenoids The primary cost of tanning is ______________________. the energy needed to produce melanin Which of the following environmental factors can affect the phenotypes expressed by a genotype? Atmospheric oxygen, Diet, Solar radiation, and humidity All individuals of a species express the same degree of plasticity. (T/F) False Plasticity is most adaptive when the environment changes __________ throughout an organism's life. slowly and predictably Acclimation Is one of the most important forms of plasticity True or False? Acclimation involves a change in the genotype triggered by a change in the environment. False, acclimation involves a change in the phenotype- no change in the genotype.
Flies from populations at fluctuating temperatures should have evolved the greatest capacity for acclimation. True Genotypes from populations at 16°C performed best when raised at 16°C and tested at 25°C. False Genotypes from all populations displayed the same degree of plasticity. False The sample size in this experiment is the number of flies in each treatment. False Flies would likely have benefitted less from acclimation if the temperature had changed several times per generation instead of once every generation. True homeostasis an organism can regulate the conditions inside its body to remain within the limits of its niche. Body continuously monitors its internal state negative feedback a mechanism that reverses a deviation from the set point. Maintains body parameters within their normal range. dynamic equilibrium body conditions fluctuate some but remain within a certain range. This range is bounded by set points. Thermoregulation Process of maintaining an internal temperature within a tolerable range even when outside temps fluctuate. Ectotherms
Can also regulate the amount of heat that they gain or lose to stay within their optimal range. Radiation Energy gained by the sun is a form of heat that raises your body temperature. Energy you radiate depends on how hot something is- this is why the sun radiates more heat than something like us. We would radiate more heat to our surroundings if we walk into somewhere cold because difference in radiation- we would be losing heat by radiation in this case. Conduction The direct transfer of heat from one substance to another substance that it is touching. Depends on the difference in temperatures- if a rock is hotter, the lizard sitting on it will gain heat. If the rock was colder it would lose heat to the rock. Convection The transfer of heat by the movement of a fluid over an object (air is a fluid). Depends on the shape of an organism. Evaporation Animal only loses heat by evaporation, never gain heat. Animal loses water, will only use sparingly and probably as a last resort. Increases as the relative humidity of the environment decreases. When an organism moves from sun to shade, it reduces heating by conduction True, reduces heat gained by radiation and by conduction (standing on the ground that is warmed or cool). Also convection, air in shade is cooler. True or False? On cloudy days, neither species thermoregulated, likely because solar radiation was absent. True Use this information and your knowledge of biology to answer the following questions. The figure below shows the body temperature of a lizard during a clear day in June. Arrows indicate times when the lizard emerged from its burrow, reached the surface of the ground, and retreated into the burrow at the end of the day.
Lower metabolism to drop body temperature True or False? An endotherm is more likely than an ectotherm to have a narrow thermal niche. True Foraging This behavior of moving from patch to patch in search of resources Optimal Strategy Maximizes the net benefit. Maximizes energy intake over time. True or False? To maximize its energy gain, the bird should remain on one tree. False What do optimality models do? Help biologists to understand phenotypes (behavior, physiology, or morphology) Catabolism Breaking down molecules from food Anabolism Supply energy for synthesizing molecules in the body Energy Budget accounts for the fraction of energy absorbed from food lost as heat through catabolism and transferred to tissues through anabolism. Catabolism fuels several cellular and physiological processes. Anabolism leads to growth and reproduction. An animal absorbs anywhere from 40% to 80% of the energy in its food, depending on its ability to digest large molecules into small ones. Of the energy absorbed: the majority passes from the covalent bonds of macromolecules to phosphate bonds of ATP through glycolysis and the electron transport chain. ATP enables cells to accomplish key functions needed to survive: Transport ions across membranes. Synthesize mRNA, proteins, and DNA. Contract and relax muscles. Digest and absorb food Generate heat for thermoregulation (in endotherms) Catabolism also generates:
Heat. Can quantify the heat produced by an organism to estimate how much catabolism occurs throughout its body. More commonly, however, biologists quantify the amount of oxygen consumed by an organism, which scales proportionally to its production of ATP and heat. Biomass: Only a small percentage of the energy from food will end up in new tissues. This energy contributes to the growth of an organism's mass. The vast majority of the energy from food will leave the body as heat. An organism that invests energy primarily in growth, likely lives in a safe environment Energy used for: Maintenance (about 50%), activity (about 30%), and growth (whatever is left) Homology any similarity between characters that is due to their shared ancestry Homoplasy occurs when characters are similar, but are not derived from a common ancestor.
