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 20.4, Problem 3R
Summary Introduction
To review:
The examples of extreme
Introduction:
The directional selection is the type of natural selection in which an extreme phenotypic character or trait is promoted due to the changes in the environment. This causes the changes in the allele frequency and the shifting of the phenotype in a fixed direction.
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Figure 19-9 shows the trait distributions before and aftera cycle of artificial selection. Does the variance of thetrait appear to have changed as a result of selection?Explain.
Is it likely that the selection coefficient (s) is similar in value for the three populations shown? Is it important to know if the amount of genetic variation for the trait under selection is approximately equal in all three populations in the graph? Why or why not?
Is each of the following examples due to directional, disruptive, balancing, or stabilizing selection?
A. Polymorphisms in snail color and banding pattern as described.
B. Thick fur among mammals exposed to cold climates
C. Birth weight in humans
D. Sturdy stems and leaves among plants exposed to windy climates
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Life: The Science of Biology
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- What are considered significant factors in maintaining the surprisinglyhigh levels of genetic variation in natural populations ?arrow_forwardWhat are two reasons why a selection limit is reached in which artificial selection no longer has an effect?arrow_forwardPlease answer questions below. How do the allelic frequencies of generations 9 to 11 compare with those in generations 1, 2, and 3? How do the allelic frequencies of generations 9 to 11 compare with each other? Cite instances in the natural setting where the phenomenon of genetic drift occurs.arrow_forward
- Which type of selection is represented in a population of birds where a wing span of 2ft rather than 1ft or 3ft is more beneficial? Directional Disruptive Stabalizingarrow_forwardIn a population that meets the Hardy–Weinberg equilibrium assumptions, 81% of the individuals are homozygous for a recessive allele. What percentage of the individuals would be expected to be heterozygous for this locus in the next generation?arrow_forwardWhat historical, social, religious, cultural, and economic factors promote genetic drift in humans? Can you think of some specific human groups in which genetic drift is likely to have occurred?arrow_forward
- In a certain breeding population , it is known for certain that only 7.8% of the individuals are "true breeding" for the dominant phenotype. What would be the predicted frequency of individuals that are "true-breeding" for the recessive phenotype?arrow_forwardIn a population at genetic equilibrium, the frequency of the homozygous recessive genotype (tt) is 0.16. What are the allele frequencies of T and t, and what are the expected frequencies of the TT and Tt genotypes?arrow_forwardUnder what scenaries is genetic drift most potent as an evolutionary process? how do factors like population size and initial allele frequences affect likelihood of an allele being lost from a population (or becoming fixed)?arrow_forward
- In a certain breeding population, it is known for certain that only 9.8% of the individuals are "true-breeding" for the dominant phenotype. What would be the predicted frequency of individuals that are "true-breeding" for the recessive phenotype?arrow_forwardIn a population at genetic equilibrium, the frequency of the dominant phenotype is 0.96. What are the frequencies of the dominant (A) and recessive (a) alleles, and what are the expected frequencies of the AA, Aa, and aa genotypes?arrow_forwardThis type of experiment, where members of an outbred populations are introduced to an inbred population as mating partners, is sometimes called a “genetic rescue”. How might measuring the average heterozygosity at a number of loci in the Swedish snake population allow you to test whether the introduced snakes had actually bred successfully with the inbred Swedish snakes?arrow_forward
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