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.1c
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?
Verified step by step guidance1
Identify the genotype of the parents: Since both parents are heterozygous carriers of 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 children using a Punnett square: Cross (mother) with (father) to find the genotypic ratio of offspring. The possible genotypes are , , and .
Calculate the probability of the second child being homozygous recessive (): From the Punnett square, the chance of is 1 out of 4, or 25%. This probability is independent of the first child's genotype because each child's genotype is an independent event.
Calculate the probability of the second child being a heterozygous carrier (): From the Punnett square, the chance of is 2 out of 4, or 50%.
Summarize the results: The chance the second child is homozygous recessive is 25%, and the chance the second child is a heterozygous carrier is 50%, regardless of the first child's genotype.
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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 occurs when a trait is expressed only if 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. For two heterozygous carriers, each child has a 25% chance of being affected, 50% chance of being a carrier, and 25% chance of being unaffected.
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Autosomal Pedigrees
Independent Assortment and Probability in Genetics
Each child’s genotype is determined independently according to Mendelian genetics, meaning the outcome for one child does not affect the probabilities for the next. Thus, even if the first child is homozygous recessive, the chance for the second child to inherit the same genotype remains the same as the initial probability.
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Genotype Probabilities for Offspring of Carrier Parents
When both parents are heterozygous carriers, the possible genotypes for each child are: 25% homozygous recessive (affected), 50% heterozygous carrier (unaffected but carrier), and 25% homozygous dominant (unaffected, non-carrier). These probabilities apply independently to each child regardless of previous offspring’s genotype.
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Related Practice
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 term is used to identify a functional protein like this one formed when two identical polypeptides join together?
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?
Textbook Question
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?