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Ch. 9 - The Molecular Biology of Translation
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 9 - The Molecular Biology of TranslationProblem B.10
Chapter 9, Problem B.10

Suppose a man and a woman are each heterozygous carriers of a mutation causing a fatal hereditary disease not on the RUSP list. Prenatal genetic testing can identify the genotype of a fetus with regard to this disease and can identify fetuses with the disease. What do you think are the three or four most important factors this couple should consider in their decision making about having children?

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1
Understand the genetic basis of the disease: Since both parents are heterozygous carriers, the disease is likely inherited in an autosomal recessive manner. This means the child must inherit two copies of the mutated gene (one from each parent) to be affected.
Calculate the probability of different genotypes in the offspring: Use a Punnett square to determine the chances of the child being homozygous normal, heterozygous carrier, or homozygous affected. For two heterozygous parents, the probabilities are typically 25% affected, 50% carrier, and 25% unaffected non-carrier.
Consider the severity and prognosis of the disease: Since the disease is fatal and hereditary, the couple should evaluate the impact on quality of life, life expectancy, and available treatments or interventions for affected children.
Evaluate the options for prenatal testing and reproductive choices: Discuss the accuracy, timing, and implications of prenatal genetic testing, as well as alternative reproductive options such as preimplantation genetic diagnosis (PGD), adoption, or use of donor gametes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Autosomal Recessive Inheritance

This disease is likely inherited in an autosomal recessive pattern, meaning both parents carry one mutated allele but are unaffected. Each child has a 25% chance of inheriting two mutated alleles and being affected, a 50% chance of being a carrier, and a 25% chance of inheriting two normal alleles. Understanding this risk is crucial for informed reproductive decisions.
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Prenatal Genetic Testing and Diagnosis

Prenatal genetic testing can determine whether a fetus has inherited the disease-causing mutations. This allows parents to make informed choices about pregnancy continuation, preparation for a child with special needs, or considering alternative reproductive options. The accuracy, timing, and implications of testing are important factors.
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Ethical and Emotional Considerations in Reproductive Decision-Making

Deciding whether to have children when there is a risk of a fatal hereditary disease involves complex ethical and emotional factors. Parents must weigh the potential quality of life for the child, their own values, possible interventions, and psychological impacts. Counseling and support are essential to navigate these challenges.
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Related Practice
Textbook Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

On the pedigree, write the genotypes (GG, Gg, or gg) for each person who has been tested or for whom you can deduce a genotype. If a genotype cannot be determined completely, list the alleles you know or deduce must be present.

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Textbook Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

Explain why you are able to assign genotypes to the man's parents despite their not being tested.

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Textbook Question

If a man and a woman are each heterozygous carriers of a mutation causing a disease on the RUSP list, what do you think are the three or four most important factors they should consider in their decision making about having children?

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Textbook Question

If you were to look up Gaucher disease on the OMIM website, you would see that there are three major types, designated Type I (OMIM 230800), Type II (OMIM 230900), and Type III (OMIM 231000). All three types are mutations of the gene for acid-β-glucosidase, encoded on chromosome 1. Different mutations of this gene produce the three types of Gaucher disease that differ somewhat in their symptoms and disease severity.

For each mutation, speculate about whether the acid-β-glucosidase enzyme is merely reduced in function or whether its production is eliminated, and explain why.

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Textbook Question

If you were to look up Gaucher disease on the OMIM website, you would see that there are three major types, designated Type I (OMIM 230800), Type II (OMIM 230900), and Type III (OMIM 231000). All three types are mutations of the gene for acid-β-glucosidase, encoded on chromosome 1. Different mutations of this gene produce the three types of Gaucher disease that differ somewhat in their symptoms and disease severity.

Thinking about the production or function of the acid-β-glucosidase enzyme, why do you suppose different mutations of this gene produce differences in symptoms and disease severity?

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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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