The pedigree above shows the inheritance of a rare human...

Name: Problem 77, Chapter 2: Introduction to Genetic Analysis
Uploaded: 2020-07-10T19:05:10-08:00
Duration: 2 min 38 s
Channel: John Barone
Description: The pedigree above shows the inheritance of a rare human disease. Is the pattern best explained as being caused by an X-linked recessive allele or by an autosomal dominant allele with expression limited to males? (Pedigree data from J. F. Crow, Genetics Notes, 6th ed. Copyright 1967 by Burgess Publishing Co., Minneapolis.)

The pedigree above shows the inheritance of a rare human disease. Is the pattern best explained as being caused by an X-linked recessive allele or by an autosomal dominant allele with expression limited to males? (Pedigree data from J. F. Crow, Genetics Notes, 6th ed. Copyright 1967 by Burgess Publishing Co., Minneapolis.)

Key Concepts

Sex-Limited Expression

Sex-limited expression describes a situation where a genetic trait appears only in one sex, despite being present in both. This phenomenon occurs when the trait is expressed due to differences in hormonal or developmental factors, even though the genetic variant is autosomal. It is important to distinguish this type of expression from true sex-linked inheritance.

X-linked Recessive Inheritance

X-linked recessive inheritance refers to a mode of genetic transmission where the mutant allele is located on the X chromosome. In this pattern, males are typically more affected because they have only one X chromosome, while females may be unaffected carriers if they possess one normal allele. This results in a higher prevalence of the trait in males when the disease allele is recessive.

Pedigree Analysis

Pedigree analysis is the study of family trees to determine the pattern of inheritance of specific traits or disorders across generations. By evaluating the occurrence of a disease in family members and identifying how traits are passed down, researchers can infer whether the inheritance follows a dominant, recessive, autosomal, or sex-linked pattern.

Autosomal Dominant Inheritance

Autosomal dominant inheritance involves traits where a single copy of the mutant allele on one of the autosomes is sufficient for an individual to express the phenotype. This pattern generally affects both sexes equally, leading to a vertical pattern in pedigrees, where the trait is passed from one generation to the next without skipping generations.

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