Ch. 3 - Mendelian Genetics

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of GeneticsISBN: 9780135564776당신이 사용하는 게 아니라요?교과서 변경

Klug 12th Edition

Ch. 3 - Mendelian Genetics

문제 23

3장, 문제 23

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.

검증된 단계별 안내

Identify the two patterns of inheritance described in the problem: one where the condition appears in every generation and another where it skips generations.

For the pattern where the condition appears in every generation, consider autosomal dominant inheritance, where a single copy of the mutant allele can cause the condition.

For the pattern where the condition skips generations, consider autosomal recessive inheritance, where two copies of the mutant allele are necessary for the condition to manifest.

In the autosomal dominant scenario, affected individuals have a 50% chance of passing the mutant allele to their offspring, leading to the condition appearing in every generation.

In the autosomal recessive scenario, carriers (heterozygous individuals) do not show symptoms, but if two carriers have children, there is a 25% chance for each child to be affected, explaining the skipping of generations.

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주요 개념

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Autosomal Dominant and Recessive Inheritance

Autosomal dominant inheritance occurs when a single copy of a mutated gene from one parent can cause a trait or disorder, leading to affected individuals in every generation. In contrast, autosomal recessive inheritance requires two copies of the mutated gene, often resulting in affected individuals appearing sporadically in a pedigree, typically when both parents are carriers. Understanding these patterns helps explain the differing occurrences of auditory neuropathy in families.

Penetrance and Expressivity

Penetrance refers to the proportion of individuals with a specific genotype that actually express the associated phenotype, while expressivity describes the degree to which a genotype is expressed in an individual. In the context of auditory neuropathy, variable penetrance could explain why some family members with the same genetic mutation may have normal hearing, while others are affected, indicating that not all individuals with the mutation will exhibit the disorder.

Mitochondrial Inheritance

Mitochondrial inheritance involves genes located in the mitochondria, which are passed exclusively from mother to offspring. This type of inheritance can lead to conditions that affect multiple family members across generations, particularly if the mother carries a mutation. In cases of auditory neuropathy, if the condition is linked to mitochondrial DNA, it could explain the presence of deafness in some family members while others remain unaffected.

관련 실천

교과서 질문

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

614

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교과서 질문

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

878

views

교과서 질문

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

1094

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교과서 질문

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. Calculate the probability that both the male and female are carriers for TSD.

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. Draw a pedigree of the families of this couple, showing the relevant individuals.

722

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