Ch. 3 - Mendelian Genetics

Klug - Concepts of Genetics 12th Edition

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Klug 12th Edition

Ch. 3 - Mendelian Genetics

Problem 22c

Chapter 3, Problem 22c

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Step 1: Identify the affected individuals and their sex in the pedigree. Here, only one female (represented by a filled circle) is affected, while all other individuals are unaffected.

Step 2: Consider the pattern of inheritance by analyzing the distribution of the trait across generations and between sexes. Since only one female is affected and no males are affected, this suggests the trait might not be Y-linked.

Step 3: Evaluate whether the trait could be autosomal dominant or recessive. If it were autosomal dominant, typically one affected parent would pass the trait to offspring, but here neither parent is affected, which argues against autosomal dominant inheritance.

Step 4: Consider X-linked inheritance. Since only a female is affected and no males, and the trait appears in only one generation, it could be consistent with X-linked recessive or dominant inheritance, but the absence of affected males makes X-linked recessive less likely.

Step 5: Summarize conclusions: The trait is likely inherited in an autosomal recessive or possibly X-linked dominant manner, but more data would be needed to confirm. The single affected female with unaffected parents suggests recessive inheritance.

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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 tool used to study the inheritance patterns of traits through generations in a family. It uses standardized symbols to represent individuals and their traits, helping to identify whether a trait is dominant, recessive, autosomal, or sex-linked. Understanding how to interpret these symbols and relationships is essential for drawing conclusions about inheritance.

Modes of Inheritance

Modes of inheritance describe how genetic traits are transmitted from parents to offspring. Common modes include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Each mode has characteristic patterns in pedigrees, such as affected individuals in every generation for dominant traits or skipping generations for recessive traits.

Sex-Linked vs. Autosomal Traits

Sex-linked traits are associated with genes located on sex chromosomes, often showing different patterns in males and females, while autosomal traits are linked to non-sex chromosomes and typically affect both sexes equally. Recognizing whether a trait affects males and females differently or equally helps determine if the trait is sex-linked or autosomal.

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Textbook Question

For decades scientists have been perplexed by different circumstances surrounding families with rare, early-onset auditory neuropathy (deafness). In some families, parents and grandparents of the proband have normal hearing, while in other families, a number of affected (deaf) family members are scattered throughout the pedigree, appearing in every generation. Assuming a genetic cause for each case, offer a reasonable explanation for the genetic origin of such deafness in the two types of families.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

Consider the following pedigree.

Predict the mode of inheritance of the trait of interest and the most probable genotype of each individual. Assume that the alleles A and a control the expression.

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Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait.

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