The mode of inheritance of cystic fibrosis is:

ESIC Nursing Officer -2019 (Shift -1)

Pathology & Genetics

Easy

Appeared in: ESIC Nursing Officer -2019 (Shift -1)

Explanation

Cystic Fibrosis (CF) is inherited in an autosomal recessive pattern, a key fact in medical genetics.
This means an individual must inherit two copies of the defective CFTR gene, one from each parent, to develop the disease.
Parents of an affected child are typically obligate carriers, meaning they each have one copy of the mutated gene but do not show symptoms of the disease themselves.
For two carrier parents, the probability of having a child with CF is 25% for each pregnancy, as illustrated by a Punnett square.

Option A: X-linked diseases are caused by mutations on the X chromosome. Cystic fibrosis is caused by a mutation on chromosome 7, which is an autosome.
Option B: In autosomal dominant inheritance, only one copy of the mutated gene is needed to cause the disease, and it typically appears in every generation. CF requires two copies and can skip generations.
Option D: Cystic fibrosis follows a predictable pattern of inheritance first described by Gregor Mendel, making it a Mendelian disorder.

Visual 1: Punnett Square - A diagram showing two heterozygous carrier parents (e.g., Ff) and the resulting 1:2:1 genotypic ratio in their offspring (FF, Ff, ff), visually demonstrating the 25% chance of an affected child.
Visual 2: Pedigree Chart - A chart illustrating an autosomal recessive inheritance pattern. It would show the disease appearing in siblings of one generation but not in the previous generation, and affecting males and females equally.

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 that CF is autosomal recessive is crucial for genetic counseling. Couples who are carriers can be informed of their risk of having an affected child and discuss reproductive options.
Newborn screening for CF is standard in many countries. Early diagnosis allows for prompt intervention, which can significantly improve long-term health outcomes by managing symptoms and nutritional needs from birth.
What if? If a person with CF has a child with a non-carrier, all their children will be obligate carriers of the CF gene, but none will have the disease. If their partner is a carrier, each child has a 50% chance of having CF.

How to Approach the Question

First, identify the core concept of the question, which is the 'mode of inheritance' for a specific disease, 'cystic fibrosis'.
This is a factual recall question. Access your knowledge base of common genetic disorders.
Systematically evaluate the options. Recall the definitions of 'autosomal recessive', 'autosomal dominant', and 'X-linked'.
Eliminate 'X-linked' as CF affects males and females equally.
Differentiate between 'dominant' (one gene copy needed, appears in every generation) and 'recessive' (two copies needed, can skip generations). CF is known to be recessive.
Confirm that CF follows predictable genetic rules, thus eliminating 'Non-Mendelian'.

Concept Tested & Keywords

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