Which is the mode of inheritance of cystic fibrosis?

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-2)

Explanation

Cystic Fibrosis (CF) is an autosomal recessive disorder, meaning an individual must inherit two defective copies of the gene to be affected.
The gene responsible is the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, located on chromosome 7.
A person who inherits only one defective gene is an asymptomatic carrier but can pass the gene to their offspring.
When two carriers have a child, there is a 25% chance the child will have CF, a 50% chance the child will be a carrier, and a 25% chance the child will be unaffected.

Option B: This is incorrect because CF follows a predictable Mendelian inheritance pattern (autosomal recessive).
Option C: This is incorrect because autosomal dominant inheritance requires only one copy of the mutated gene to cause the disease.
Option D: This is incorrect because the gene for CF is on an autosome (chromosome 7), not a sex chromosome.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mode of inheritance for Cystic Fibrosis as background academic context rather than a clinical decision trigger.
Understanding the autosomal recessive inheritance of CF is crucial for patient and family education, particularly regarding genetic counseling and family planning.
Nurses must be able to explain to at-risk couples (e.g., those with a family history of CF) their chances of having an affected child and the availability of carrier screening.
What if? If only one parent is a carrier of the CF gene and the other is not, there is a 0% chance their child will have CF. However, there is a 50% chance that each child will be a carrier, just like the carrier parent.

How to Approach the Question

First, identify the core of the question, which is asking for the specific genetic inheritance pattern of Cystic Fibrosis.
This is a factual recall question. Access your knowledge base about common genetic disorders.
Recall that Cystic Fibrosis is one of the most well-known autosomal recessive diseases.
Evaluate the options: 'Autosomal recessive' directly matches your knowledge. 'Autosomal dominant' and 'X-linked' are different, incorrect patterns. 'Non-Mendelian' is a broad category that CF does not fall into.
Select the option that accurately describes the inheritance of CF.

Concept Tested & Keywords

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 472-474

E6 Medicine Davidson Principles Practice 24e p. 600-602

E6 Nursing Brunner Adult Health 3SA Vol 1 Part 2 p. 60-62

Practise the full RRB Nsg. Superintendent-20 July 2019 (Shift-2)

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