BIOLOGY
BIOLOGY
12th Edition
ISBN: 9781260169614
Author: Raven
Publisher: RENT MCG
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Chapter 20, Problem 3S

Based on a consideration of how strong artificial selection has helped eliminate genetic variation for speed in thoroughbred horses, we are left with the question of why, for many traits like speed (continuous traits), there is usually abundant genetic variation. This is true even for traits we know are under strong selection. Where does genetic variation ultimately come from, and how does the rate of production compare with the strength of natural selection? What other mechanisms can maintain and increase genetic variation in natural populations?

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If gene A/a is not in Hardy-Weinberg equilibrium due to natural selection such that individuals with the genotype AA have a fitness value of 1.0, heterozygotes have only slightly reduced fitness at 0.9, and individuals with the genotype aa have a fitness value of 0.6, what kind of change in allele frequency would you expect to see over time assuming you start with equal frequencies of the 2 alleles?
Selection confers a reproductive advantage to individuals based on their adaptations, and therefore causes the alleles carried by those individuals to increase in the population. Selection can be simulated by having your partner remove any three individuals of a particular suit as you deal the cards into a pile. The fitness of that variant is therefore 0.77 (10/13 survive), while the fitness of the other three variants remains at 1.0 (13/13 survive). Recalculate allelic (suit) frequencies after selection. 1. What is the effect of selection on reproduction, allelic diversity, and frequency? 2. What would happen if similar selection continued over several generations?   Cite references.
Some genetic disorders are caused by autosomal recessive alleles. Many such alleles are recessive lethals, causing lethality very early in life (say, before the age of 20 yrs). Intuitively one might suggest that selection working on human population should completely remove such alleles from the population. Yet, there are many examples of such lethal genetic disorders occurring in low frequency in several human populations. Why is it almost impossible to completely remove these seemingly fitness-detrimental alleles from the population? Under what condition, extinction of such an allele from a population can be achieved?

Chapter 20 Solutions

BIOLOGY

Ch. 20.5 - Prob. 1LOCh. 20.5 - Prob. 2LOCh. 20.5 - Prob. 3LOCh. 20.6 - Define frequency-dependent selection, oscillating...Ch. 20.6 - Prob. 2LOCh. 20.7 - Define and contrast disruptive, directional, and...Ch. 20.7 - Prob. 2LOCh. 20.8 - Explain how experiments can be used to test...Ch. 20.9 - Prob. 1LOCh. 20.9 - Prob. 2LOCh. 20.10 - Prob. 2LOCh. 20 - If all white cats died, what proportion of the...Ch. 20 - Assuming that the values on the x-axis represent...Ch. 20 - Prob. 3DACh. 20 - Prob. 4DACh. 20 - Examine the index of copper tolerance on nonmine...Ch. 20 - Prob. 6DACh. 20 - Why are rare alleles particularly likely to be...Ch. 20 - Prob. 2IQCh. 20 - Prob. 3IQCh. 20 - Prob. 4IQCh. 20 - Prob. 5IQCh. 20 - Prob. 6IQCh. 20 - Prob. 7IQCh. 20 - Prob. 8IQCh. 20 - Prob. 9IQCh. 20 - Assortative mating a. affects genotype frequencies...Ch. 20 - When the environment changes from year to year and...Ch. 20 - Many factors can limit the ability of natural...Ch. 20 - Stabilizing selection differs from directional...Ch. 20 - Founder effects and bottlenecks are a. expected...Ch. 20 - Relative fitness a. refers to the survival rate of...Ch. 20 - For natural selection to result in evolutionary...Ch. 20 - Prob. 8UCh. 20 - In a population of red (dominant allele) or white...Ch. 20 - Genetic drift and natural selection can both lead...Ch. 20 - Prob. 3ACh. 20 - Prob. 4ACh. 20 - In Trinidadian guppies a combination of elegant...Ch. 20 - On large, black lava flows in the deserts of the...Ch. 20 - Based on a consideration of how strong artificial...
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