Textbook Question
George Udny Yule was wrong in suggesting that an autosomal dominant trait like brachydactyly will increase in frequency in populations. Explain why Yule was incorrect.
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Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
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Sanders 3rd EditionCh. 20 - Population Genetics and Evolution at the Population, Species, and Molecular LevelsProblem 10c
Sanders 3rd EditionCh. 20 - Population Genetics and Evolution at the Population, Species, and Molecular LevelsProblem 10cChapter 20, Problem 10c
The ability to taste the bitter compound phenylthiocarbamide (PTC) is an autosomal dominant trait. The inability to taste PTC is a recessive condition. In a sample of 500 people, 360 have the ability to taste PTC and 140 do not. Calculate the frequency of each genotype.
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Step 1: Define the alleles and genotypes. Let 'T' represent the dominant allele for the ability to taste PTC, and 't' represent the recessive allele for the inability to taste PTC. The genotypes are TT (homozygous dominant), Tt (heterozygous), and tt (homozygous recessive).
Step 2: Use the Hardy-Weinberg principle to model the population. The Hardy-Weinberg equation is p² + 2pq + q² = 1, where p is the frequency of the dominant allele (T), q is the frequency of the recessive allele (t), p² represents the frequency of TT, 2pq represents the frequency of Tt, and q² represents the frequency of tt.
Step 3: Calculate q², the frequency of the homozygous recessive genotype (tt). Since 140 out of 500 people cannot taste PTC, the frequency of the recessive phenotype is 140/500 = 0.28. This is equal to q².
Step 4: Solve for q, the frequency of the recessive allele. Take the square root of q² to find q. Use the equation q = √(q²).
Step 5: Calculate p, the frequency of the dominant allele. Use the relationship p + q = 1 to solve for p. Then, calculate the frequencies of each genotype: p² for TT, 2pq for Tt, and q² for tt. These represent the proportions of the population with each genotype.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Autosomal Dominance and Recessiveness
In genetics, traits can be classified as dominant or recessive based on how they are expressed in an organism. An autosomal dominant trait, like the ability to taste PTC, requires only one copy of the dominant allele for expression, while a recessive trait requires two copies of the recessive allele. This distinction is crucial for understanding inheritance patterns and predicting genotype frequencies in a population.
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Variations on Dominance
Hardy-Weinberg Principle
The Hardy-Weinberg Principle provides a mathematical framework for understanding genetic variation in a population at equilibrium. It states that allele and genotype frequencies will remain constant from generation to generation in the absence of evolutionary influences. This principle is essential for calculating genotype frequencies based on observed phenotypic ratios, as it allows for predictions about genetic diversity.
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Genotype Frequency Calculation
Genotype frequency refers to the proportion of different genotypes in a population. To calculate these frequencies, one can use the observed phenotypic data along with the principles of inheritance. For the PTC tasting trait, knowing the number of tasters and non-tasters allows for the application of the Hardy-Weinberg equations to derive the frequencies of the homozygous dominant, heterozygous, and homozygous recessive genotypes.
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Related Practice
Textbook Question
The ability to taste the bitter compound phenylthiocarbamide (PTC) is an autosomal dominant trait. The inability to taste PTC is a recessive condition. In a sample of 500 people, 360 have the ability to taste PTC and 140 do not. Calculate the frequency of the recessive allele.
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Textbook Question
The ability to taste the bitter compound phenylthiocarbamide (PTC) is an autosomal dominant trait. The inability to taste PTC is a recessive condition. In a sample of 500 people, 360 have the ability to taste PTC and 140 do not. Calculate the frequency of the dominant allele.
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Textbook Question
The figure illustrates the effect of an ethanol-rich and an ethanol-free environment on the frequency of the Drosophila AdhF allele in four populations in a 50-generation laboratory experiment. Population 1 and population 2 were reared for 50 generations in a high-ethanol environment, while control 1 and control 2 populations were reared for 50 generations in a zero-ethanol environment. Describe the effect of each environment on the populations, and state any conclusions you can reach about the role of any of the evolutionary processes in producing these effects.
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Textbook Question
Biologists have proposed that the use of antibiotics to treat human infectious disease has played a role in the evolution of widespread antibiotic resistance in several bacterial species, including Staphylococcus aureus and the bacteria causing gonorrhea, tuberculosis, and other infectious diseases. Explain how the evolutionary mechanisms mutation and natural selection may have contributed to the development of antibiotic resistance.
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Textbook Question
Two populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland. If you compared the allele frequencies in the two populations, what would you expect to find?
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