Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
Publisher: W. H. Freeman
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Chapter 20.5, Problem 3R
Summary Introduction
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The presence of variations at the genetic level in a population, which may elevate the chances that certain members of the population might survive unpredictable environment change, but there is no guarantee that this would be the case.
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Why is a balancedfrequency of different allelesof a gene in a population moreuseful for the survival of thatpopulation facingenvironmental changes?
Two populations of snakes are separated by a river. The snakescross the river only on rare occasions. The snakes in the two populationslook very similar to each other, except that the members ofthe population on the eastern bank of the river have a yellow spoton the top of their head, whereas the members of the western populationhave an orange spot on the top of their head. Discuss twoexperimental methods that you might use to determine whether thetwo populations are members of the same species or members ofdifferent ones.
The original source of new alleles, upon which selection operates,is mutation, a random event that occurs without regard to selectionalvalue in the organism. Although many model organismshave been used to study mutational events in populations, someinvestigators have developed abiotic molecular models. Soll et al.(2006. Genetics 175:267–275) examined one such model to studythe relationship between both deleterious and advantageousmutations and population size in a ligase molecule composed ofRNA (a ribozyme). Soll found that the smaller the population ofmolecules, the more likely it was that not only deleterious mutationsbut also advantageous mutations would disappear. Whywould population size influence the survival of both types ofmutations (deleterious and advantageous) in populations?
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Life: The Science of Biology
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- Pikas are small mammals that live at high elevations on the talus slopesof mountains. Most populations located on mountaintops in Coloradoand Montana in North America are isolated from one another: the pikasdon’t occupy the low-elevation habitats that separate the mountaintopsand don’t venture far from the talus slopes. Thus, there is little gene flowbetween populations. Furthermore, each population is small in size andwas founded by a small number of pikas.A group of population geneticists proposes to study the amount ofgenetic variation in a series of pika populations and to compare theallelic frequencies in different populations. On the basis of the biologyand distribution of pikas, predict what the population geneticists willfind concerning the within- and between-population genetic variation.arrow_forwardConsider the first copy of an allele for insecticideresistance that arises by mutation in a populationof insects exposed to an insecticide. Is this mutation an adaptation? If, after some generations,we find that most of the population is resistant,is the resistance an adaptation? If we discovergenetic variation for insecticide resistance in apopulation that has had no experience of insecticides, is the variation an adaptation? If an insectpopulation is polymorphic for two alleles, eachof which confers resistance against one of twopesticides that are alternately applied, is thevariation an adaptation? Or is each of the tworesistance traits an adaptation?arrow_forwardMicroevolution is defined as a change inallele frequencies in a population over generations. Please explainwhat an allele is, in genetic terms. Name the three major factorsinvolved in allele frequency changes in populations. Describe, indetail, how natural selection works on individuals, while evolutionoccurs in populations. Include a real or hypothetical example ofthe process of natural selection in your answer other thaninsects and insecticide! Identify the specific natural selectionpressure and the specific trait being selected for in yourexample.arrow_forward
- Imagine that you are asked to manage a population of wolves that have taken upresidence on an island off the coast of Alaska. Because prey resources are limited, theisland will support only about 50 wolves at any one time. What steps would you take toprevent inbreeding and genetic drift in the population in the future?arrow_forwardNatural selection tends to work toward genetic unity;the genotypes that are most fit produce the mostoffspring and increase the frequency of adaptive allelesin the population. Yet there remains a great deal ofvariability within the populations of species. Describethe factors that contribute to this genetic variability. Provide the link of referencesarrow_forwardEntomologists at the New York State Department of Agriculture are interested in determiningthe connection between pest insects infesting crop plants with populations of the same insectinfesting native plants in natural habitats. Long term trapping and monitoring studies haveestimated that on average 3% of the populations move between habitats (farm to natural and visversa) each generation. A new insecticide resistance allele (∆K) has begun to increase infrequency in the agricultural populations. A genotyping survey at this locus of 50 individuals ineach population has revealed the following genotype counts: K/K K/∆K ∆K/∆K Agricultural field 32 16 2 Forest 48 2 0 4a. Based on the effects of migration alone, what will the frequency of ∆K be in the forestpopulation in the next generation? 4b. If migration was acting in here without selection, what would the frequency of ΔK be in theagricultural population in the next generation? 4c. If the natural forest population was…arrow_forward
- For a locus with two alleles (B and b) in a population at riskfrom an infectious neurodegenerative disease, 16 individualshave the genotype BB, 92 individuals have Bb and 12individuals have bb. Use the Hardy-Weinberg equation todetermine whether this population appears to be evolving.arrow_forwardCana a change in the physical enviroment of a population result in evolution by natural slection?(hint: remember the peppered moth's camouflage and color changes of tree bark due to pollution)arrow_forward(b) Suppose that we want to model the evolution of the population of a cer- tain type of organisms. Observations indicate that if the population drops below a survival level of 10° individuals, it goes extinct. Moreover, the population growth is limited: the available resources of space and food can sustain at most 106 individuals. We treat the population size P(t) as a continuous function of time. (i) Explain briefly how the following model incorporates the above ob- servations: dP — К(А- Р)(Р — В), k>0, dt where P(t) denotes the population size at time t and B 0. dt Find the equilibrium values and determine their stability. [6]arrow_forward
- In a population of lizards, color is genetically determined. The current population has two two phenotypes: blue and yellow. Which of the following scenarios could result in evolution by migration? O A disease indiscriminately reduces the population by 90%. Birds are better able to see and therefor prey on blue lizards The population is joined by individuals from a nearby population that has an allele for a red phenotype. Females preferentially mate with individuals exhibiting the blue phenotype.arrow_forwardThree basic predictions underlie genetic drift in populations: (1) As long as the population size is finite,some level of genetic drift will occur; thus, withoutnew mutations, all variation will drift either to fixationor to loss. (2) Drift happens faster in small populationsthan in large populations. (3) The probability that anallele is fixed (goes to a frequency of 1.0) is equal toits initial frequency (p) in the population, while itsprobability of loss from the population due to drift isequal to 1 − p. Given these three predictions:a. What is the allele frequency of a new autosomalmutation immediately after it occurs in a diploidpopulation of size N = 100,000?b. What is the allele frequency of a new autosomalmutation immediately after it occurs in a diploidpopulation of size N = 10?c. In which population does the new mutation have ahigher probability of going to fixation by chancewith genetic drift?arrow_forwardtell whether the curves for the different cohorts are different from one another.If so, what might have caused the differences? In addition, did you notice any difference in the curves for males and females? If so, what might havecaused the differences?Speculate about the future if: 1) health care costs continues to increase, and 2) medical advances continueand most diseases and infant mortality are eliminated.How can this method be used to understand or manage natural populations?arrow_forward
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