EBK LIFE: THE SCIENCE OF BIOLOGY
11th Edition
ISBN: 8220103935432
Author: Sadava
Publisher: MAC HIGHER
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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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Why do we have to consider the mean fitness across all environments when evaluating whether evolving a phenotypically plastic genotype will be favored over a non-plastic genotype?
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Mutations of small effect are more likely to be advantageous than mutations of large effect.
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At least one of the discoverers of this genetic equilibrium (Hardy) developed this HW equation to show that the dominant allele will not always take over the population just because that allele has a dominant effect on the phenotype. What additional factor would have to be present to cause a dominant allele to increase to a frequency of 100%? Why is this factor essential for the dominant allele to “take over” the gene pool?
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EBK LIFE: THE SCIENCE OF BIOLOGY
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- Explain how natural selection might be responsible for the PTC taster polymorphism.Why might some populations have a higher frequency of the taster allele than others?arrow_forwardWhat are two reasons why a selection limit is reached in which artificial selection no longer has an effect?arrow_forwardHow does the concept of artificial selection is applied in the creation and domestication of chihuahuas out of wolves? Explain in an explicit way.arrow_forward
- The effect(s) of the environment on the variation seen in phenotypes include: influencing the heritability of the phenotype influencing the phenotype's response to selection allowing continuous phenotypic variance from a discrete genetic basis all of the above a) and b) only O a) and c) only b) and c) onlyarrow_forwardWhat are considered significant factors in maintaining the surprisinglyhigh levels of genetic variation in natural populations ?arrow_forwardLet’s suppose that pigmentation in a species of insect is controlledby a single gene that exists as two alleles, D for dark and d for light.The heterozygote, Dd, is intermediate in color. In a heterogeneousenvironment, the allele frequencies are D = 0.7 and d = 0.3. Thispolymorphism is maintained because the environment has somedimly lit forested areas and some sunny fields. During a hurricane,a group of 1000 insects is blown to a completely sunny area. In thisenvironment, the relative fitness values are DD = 0.3, Dd = 0.7, anddd = 1.0. What are the predicted allele frequencies in thenext generation?arrow_forward
- Consider 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_forwardWhich microevolutionary force typically changes genotype frequencies without changing allele frequencies? Explain.arrow_forwardIn New Zealand you begin to study the relationship between snails and their trematode parasites. You found that the parasites cause cyclical patterns of selection on the snail populations, and vice a versa, such that snails with rare genotypes typically survive better compared to those that have more common genotypes. In the ten years you’ve been sampling, you notice that the two alleles cycle between being rare and common from year to year. What pattern of selection did you observe? a. selection against the dominant allele b. selection against the recessive allele c. frequency-dependent selection d. overdominancearrow_forward
- The forward mutation rate for piebald spotting in guinea pigs is 8 × 10-5;the reverse mutation rate is 2 × 10-6. If no other evolutionary forces areassumed to be acting, what is the expected frequency of the allele forpiebald spotting in a population that is in mutational equilibrium?arrow_forwardIs 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?arrow_forwardAsaparrow_forward
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