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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.6b
Chapter 9, Problem B.6b

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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Identify the alleles involved: G is the dominant normal allele, and g is the recessive mutant allele causing Gaucher disease. Individuals with genotype gg have the disease, Gg are carriers, and GG are unaffected non-carriers.
Start with the woman: she is homozygous dominant (GG), so both her alleles are G. This means she inherited one G allele from each parent.
Analyze the woman's family: her father, sister, and paternal grandmother are heterozygous carriers (Gg), so each has one G and one g allele. Her paternal grandfather, mother, and maternal grandparents are homozygous dominant (GG). Use this information to assign genotypes to these individuals.
Consider the man: he is heterozygous (Gg), so he carries one G and one g allele. Since he has a brother with Gaucher disease (gg), both parents must carry at least one g allele, even though they are not tested and do not have the disease themselves (implying they are likely Gg).
For any individuals without direct test results, use Mendelian inheritance rules and the known genotypes of their relatives to deduce possible genotypes or at least the alleles they must carry. If a genotype cannot be fully determined, list the alleles that must be present based on inheritance.

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Key Concepts

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

Mendelian Inheritance and Allele Dominance

Mendelian inheritance explains how alleles are transmitted from parents to offspring following dominant and recessive patterns. A dominant allele (G) masks the effect of a recessive allele (g) in heterozygotes. Understanding which alleles are dominant or recessive helps predict genotypes and phenotypes in pedigrees.
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Variations on Dominance

Carrier Status and Genotype Deduction

Carriers are individuals who possess one copy of a recessive mutant allele (g) but do not show disease symptoms due to the presence of a dominant normal allele (G). By analyzing family relationships and known genotypes, one can deduce unknown genotypes based on inheritance patterns and the presence or absence of disease.
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Gamete Genotypes

Pedigree Analysis and Genotype Assignment

Pedigree analysis involves mapping family relationships and phenotypes to infer genotypes. Using information about affected individuals and carriers, genotypes can be assigned or partially deduced for relatives. This method is essential for understanding genetic risks and inheritance in families.
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Pedigree Flowchart
Related Practice
Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

Why do you think eating a low-methionine diet is critical to controlling homocystinuria?

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Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

The low-methionine diet must be maintained throughout life to manage homocystinuria. Why do you think this is the case?

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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.

Draw a pedigree of this family, including the woman, the man, their siblings, parents, and grandparents.

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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

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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