Identify the disorder when a single gene in the heterozygous state is capable of producing a phenotype?

Appeared in: DSSSB - 29 August 2019 (Shift-1)

Explanation

Autosomal dominant disorders are defined by the expression of a phenotype in the heterozygous state, meaning only one copy of the mutated gene is needed.
The term 'dominant' signifies that this single allele's effect masks the corresponding 'recessive' allele on the other chromosome.
This matches the question's description of a single gene in a heterozygous state producing a phenotype.
In this pattern, an affected person has at least one affected parent, and there is a 50% probability of passing the gene to each child.

Option A: Multifactorial disorders are caused by the interaction of multiple genes and environmental factors, not a single gene as stated in the question.
Option C: Autosomal recessive disorders require two copies of the mutated gene (homozygous state) to express the phenotype. A heterozygous individual is a carrier but does not show the trait.
Option D: X-linked disorders are specifically related to genes on the X chromosome. While some can be dominant, 'autosomal dominant' is the broader, more precise term for the general principle described, which applies to non-sex chromosomes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Genetic Inheritance Patterns as background academic context rather than a clinical decision trigger.
Understanding inheritance patterns is crucial for patient education and genetic counseling. Nurses often take detailed family histories to identify potential genetic risks.
For autosomal dominant disorders, it's important to counsel patients that each child has a 50% chance of inheriting the condition, which can influence family planning decisions.
Predictive genetic testing may be available for individuals with a family history of a dominant disorder, allowing for early detection and management.

How to Approach the Question

First, identify the key terms in the question: 'single gene', 'heterozygous state', and 'phenotype'.
Define each term. 'Heterozygous' means having one copy of the mutated allele and one normal allele.
Review the definitions of the different inheritance patterns provided in the options.
An 'autosomal dominant' disorder is one where a single copy of a mutated gene is enough to cause the disease (express the phenotype).
An 'autosomal recessive' disorder requires two copies of the mutated gene.
Match the definition from the question to the correct inheritance pattern. The question's description directly defines an autosomal dominant disorder.

Concept Tested & Keywords

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed pp. 151-153, 152-154

Practise the full DSSSB - 29 August 2019 (Shift-1)

Attempt every question from this paper in a timed mock, then review the full solution for each one.