Human Heredity: Principles and Issues (MindTap Course List)
11th Edition
ISBN: 9781305251052
Author: Michael Cummings
Publisher: Cengage Learning
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Chapter 19, Problem 20QP
Natural Selection Affects the Frequency of Genetic Disorders
Will a recessive allele that is lethal in the homozygous condition ever be completely removed from a large population by natural selection?
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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?
The agouti gene determines coat colour in mice. Heterozygous mice have yellow coats, while homozygous dominant mice have black coats. However, having two copies of the recessive alleles is lethal. In a population of 2 000 mice, 1 082 mice have black coats.
a) Calculate the frequency of each allele. Show all your work and express your answer as a value between 0 and 1 rounded to two decimal places.
b) What percentage of the mouse population is expected to be carriers of the lethal allele? Show all your work and express your answer rounded to one decimal place.
c) How many mice will die during fetal development? Show all your work and round your answer to the closest whole number.
The eugenic movement was created in the early 20th century by Sir Francis Galton. Its aim was to improve the genetic pool of the human population by selective breeding. One idea was to discourage individuals with Mendelian autosomal recessive diseases to have children. However, the fallacy of this idea is shown by the fact that recessive lethal alleles (that are never found in homozygosity) can persist in populations for hundreds to thousands of generations. Which one of the following statements best explains the persistence of those alleles in populations?
There is heterozygote advantage in those populations.
Recessive alleles keep being produced by mutation.
Recessive alleles cannot be selected against when present in heterozygotes.
Genetic drift keeps recessive alleles at a relative high frequency in populations.
Consider the action of mutation and of genetic drift in a population. What do you expect genetic variation will be in a…
Chapter 19 Solutions
Human Heredity: Principles and Issues (MindTap Course List)
Ch. 19.8 - Why dont genetic markers on the Y chromosome...Ch. 19.8 - Prob. 2GRCh. 19 - If you suspected that heterozygous carriers of a...Ch. 19 - If allele frequencies in the hemoglobin gene are...Ch. 19 - Prob. 1QPCh. 19 - How Can We Measure Allele Frequencies in...Ch. 19 - How Can We Measure Allele Frequencies in...Ch. 19 - Prob. 4QPCh. 19 - Prob. 5QPCh. 19 - How Can We Measure Allele Frequencies in...
Ch. 19 - How Can We Measure Allele Frequencies in...Ch. 19 - How Can We Measure Allele Frequencies in...Ch. 19 - Using the HardyWeinberg Law in Human Genetics...Ch. 19 - Prob. 10QPCh. 19 - Using the HardyWeinberg Law in Human Genetics In a...Ch. 19 - Prob. 12QPCh. 19 - Measuring Genetic Diversity in Human Populations...Ch. 19 - Measuring Genetic Diversity in Human Populations...Ch. 19 - Prob. 15QPCh. 19 - Measuring Genetic Diversity in Human Populations...Ch. 19 - Prob. 17QPCh. 19 - Prob. 18QPCh. 19 - Measuring Genetic Diversity in Human Populations...Ch. 19 - Natural Selection Affects the Frequency of Genetic...Ch. 19 - Prob. 21QPCh. 19 - Prob. 22QPCh. 19 - The Evolutionary History and Spread of Our Species...Ch. 19 - Prob. 24QPCh. 19 - Genomics and Human Evolution The Denisovan genome...
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- The Galapagos Islands are home to a unique iguana species that dives for extended periods of time to feed on algae from the sea floor. This makes them the world's only marine lizard. Assume the scales of these iguanas exhibit two phenotypes controlled by a single gene with two alleles: dominant, brown (G) and recessive, green (g). After studying the population for many years, a group of scientists concluded that a mess of 10,000 iguanas was not evolving, and that this mess contained 30% brown alleles and 70% green alleles. a) What is the expected frequency of each genotype for scale color? b) What is the expected number of individuals with each phenotype? Much to the researchers' dismay, one year during an EI Niño cycle, food became scarce and the mess of iguanas was randomly reduced to 100 individuals: 75 brown and 25 green. The researchers then conducted a genetic study on these individuals and found that of the 75 brown individuals, 30 were heterozygous. c) What is the actual…arrow_forwardYou are studying an autosome trait. There are two alleles, one showing complete dominance over the other. In a population, 84% of the individuals show the dominant phenotype. Assuming that this population is under Hardy-Weinberg equilibrium, which of the following statement is TRUE? 36% of individuals have the homozygous dominant genotype. 40% of the alleles in the population is recessive. 16% of the alleles in the population is recessive. 60% of individuals have the dominant alleles.arrow_forwardWhy do recessive lethals persist in a population? Provide an example of a recessive lethal allele.arrow_forward
- Why is the elimination of a fully recessive deleteriousallele by natural selection difficult in a large populationand less so in a small population?arrow_forwardLets say there exists a gene in the United States that comes in two alleles, the dominant A and the recessive a. The allele frequency of the dominant allele is 60% and the allele frequency of the recessive allele is 40% The population in genotyped and its found in the United States there are 36% Homozygous Dominant folk, 48% Homozygous Recessive folk, and 16% Homozygous recessive folk. Do you think there is any fitness advantage to any of these genotypes? Why or why not? View keyboard shortcutsarrow_forwardThe delta-32 mutation, a recessive gene, gives humans protection from HIV infection. The allele frequency in a town in Sweden is 20%. What percent of the population have two copies of the gene and are therefore immune to HIV? What percent of the population are less susceptible to the disease since they are heterozygous?arrow_forward
- if the recessive allele r is lethal, what genotypes will natural selection benefits ?arrow_forwardNatural selection means that the environment favors survival of some genotypes. From where does diversity in genotypes come?arrow_forwardIs it easier for selection to remove a deleterious recessive allele from a randomly mating population or from a highly inbred population? Why?arrow_forward
- In Africa we find albinism in around 1 in every 5,000 individuals. This is puzzling, because albinism may reduce survival, for instance due to increased risk of skin cancer. What evolutionary mechanism (natural selection, mutation, genetic drift, or gene flow) is a viable explanation for the consistent observation of a few children born with albinism each generation and why?arrow_forwardA hypothetical population has two alleles for an "T" gene: T and t. In a random sample of 50 diploid zygotes (for a total of following genotypes were found: 15 TT, 25 Tt, and 10 tt. Let's say that natural selection acts against the t allele in the initial population sampled above, and all 10 individuals with tt genotype die off (leaving 0 tt individuals) and 10 of the individuals with Tt genotype die off (leaving 15 Tt individuals) before reaching maturity. (The number of surviving adults in the population is 30). Is this population at Hardy-Weinberg equilibrium? alleles), the O A. Yes O B. Noarrow_forwardNASA is planning on sending a colony of Snow Monkeys to mars to determine how evolution will progress outside of our planet. They have calculated the following for 226 individuals: Observed Genotype Frequencies (not in HWE) AA: 0.392 Aa: 0.445 aa: 0,163 If this population was in Hardy Weinberg Equilibrium, what would be the expected number of individuals for the homozygous recessive? Retain 1 decimal place.arrow_forward
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