Textbook Question
Answer the following questions for autosomal conditions such as PKU.
If both parents are heterozygous carriers of a mutant allele, what is the chance that their first child will be homozygous recessive for the mutation?
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Ch. 9 - The Molecular Biology of Translation
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
Chapter 9, Problem B.1b
Answer the following questions for autosomal conditions such as PKU.
Parents who are each heterozygous carriers for a recessive mutant allele have a child who does not have the condition. What is the chance this child is a heterozygous carrier of the condition?
Verified step by step guidance1
Identify the genotype of the parents: Since both parents are heterozygous carriers for a recessive mutant allele, their genotypes can be represented as , where is the normal allele and is the recessive mutant allele.
Determine the possible genotypes of their child using a Punnett square: The possible genotypes are (homozygous normal), (heterozygous carrier), and (affected with the condition). The expected genotypic ratio is 1 : 2 : 1 .
Since the child does not have the condition, exclude the genotype from consideration. This leaves the possible genotypes for the child as either or .
Calculate the conditional probability that the child is a heterozygous carrier () given that the child is not affected. Use the formula: .
Substitute the values from the Punnett square into the formula to find the chance that the child is a heterozygous carrier given they do not have the condition.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Autosomal Recessive Inheritance
Autosomal recessive inheritance means a condition manifests only when an individual inherits two copies of a mutant allele, one from each parent. Carriers have one normal and one mutant allele but typically do not show symptoms. Understanding this pattern helps predict the likelihood of offspring being affected or carriers.
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Autosomal Pedigrees
Genotype Probabilities in Carrier Parents
When both parents are heterozygous carriers, each child has a 25% chance of being affected (homozygous recessive), 50% chance of being a carrier (heterozygous), and 25% chance of being unaffected and not a carrier (homozygous dominant). These probabilities are derived from a Punnett square analysis.
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Conditional Probability Given Phenotype
If a child does not have the condition (is unaffected), the probability that the child is a carrier changes because the affected genotype is excluded. This requires calculating the conditional probability of being heterozygous given the child is not affected, adjusting the original genotype probabilities accordingly.
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Related Practice
Textbook Question
Answer the following questions for autosomal conditions such as PKU.
If the first child of parents who are both heterozygous carriers of a recessive mutant allele is homozygous recessive, what is the chance the second child of the couple will be homozygous recessive? What is the chance the second child will be a heterozygous carrier of the recessive mutation?
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Textbook Question
Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein. What is the amino acid sequence of the polypeptide produced from this sequence?
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