Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes

Problem 12

Chapter 17, Problem 12

What type or types of inheritance are consistent with the following pedigree?

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Examine the pedigree chart carefully. Note that affected individuals are represented by filled symbols (black circles or squares), while unaffected individuals are represented by unfilled symbols (white circles or squares).

Identify the inheritance pattern by observing how the trait is passed through generations. In this chart, affected individuals appear in both males and females, suggesting it is not sex-linked.

Notice that affected individuals in generation II (individuals 2, 3, and 4) have unaffected parents in generation I. This suggests that the trait could be recessive, as it skips a generation.

Check for any evidence of maternal inheritance. If the trait is passed exclusively through the maternal line (e.g., all offspring of an affected mother are affected), it could indicate mitochondrial inheritance. However, this pattern is not observed here.

Conclude that the inheritance pattern is most consistent with autosomal recessive inheritance, as the trait appears in both sexes and skips a generation, with affected individuals having unaffected parents.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance of traits through generations in a family. It helps identify patterns of inheritance, such as dominant or recessive traits, by analyzing the phenotypes of individuals and their relationships. Symbols in a pedigree chart represent individuals, with filled shapes indicating affected individuals and unfilled shapes indicating unaffected ones.

Autosomal Dominant Inheritance

Autosomal dominant inheritance occurs when a trait is expressed in individuals who have at least one copy of the dominant allele. This pattern typically shows affected individuals in every generation, with both males and females equally likely to inherit the trait. In a pedigree, this is indicated by the presence of affected individuals in successive generations, often with one affected parent.

Autosomal Recessive Inheritance

Autosomal recessive inheritance requires two copies of the recessive allele for the trait to be expressed. Affected individuals often have unaffected parents who are carriers. This pattern may skip generations, as carriers can pass the allele without showing the trait. In a pedigree, this is shown by affected individuals appearing in families where the trait is not present in every generation.

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Related Practice

Textbook Question

Consider the phylogenetic tree presented in the following figure (Figure 17.17). How were the origins of secondary endosymbiosis in the brown algae determined?

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Textbook Question

You are a genetic counselor, and several members of the family whose pedigree for an inherited disorder is depicted in Genetic Analysis 17.2 consult with you about the probability that their progeny may be afflicted. What advice would you give individuals III-1, III-2, III-4, III-6, III-8, and III-9?

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Textbook Question

You have isolated two petite mutants, pet1 and pet2, in Saccharomyces cerevisiae. When pet1 is mated with wild-type yeast, the haploid products following meiosis segregate 2:2 (wild type : petite). In contrast, when pet2 is mated with wild type, all haploid products following meiosis are wild type. To what class of petite mutations does each of these petite mutants belong? What types of progeny do you expect from a pet1 × pet2 mating?

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Textbook Question

Consider this human pedigree for a vision defect.

What is the most probable mode of inheritance of the disease? Identify any discrepancies between the pedigree and your proposed mode of transmission, and provide possible explanations for these exceptions.

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Textbook Question

A mutation in Arabidopsis immutans results in the necrosis (death) of tissues in a mosaic configuration. Examination of the mitochondrial DNA detects deletions of various regions of the mitochondrial genome in the tissues that are necrotic. When immutans plants are crossed with wild-type plants, the are wild type, and the are wild type and immutans in a 3:1 ratio. Explain the inheritance of the immutans mutation and a possible origin of the mitochondrial DNA deletions.

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Textbook Question

You have isolated (1) a streptomycin-resistant mutant (strᴿ) of Chlamydomonas that maps to the chloroplast genome and (2) a hygromycin-resistant mutant (hygᴿ) of Chlamydomonas that maps to the mitochondrial genome. What types of progeny do you expect from the following reciprocal crosses?

mt⁺ strᴿ hygˢ× mt⁻ strˢ hygᴿ

mt⁺ strˢ hygᴿ× mt⁻ strᴿ hygSˢ

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