In the following human pedigree, the filled symbols represent the affected individuals. Identify the type of given pedigree?

Appeared in: NORCET 3 - 2022 (Shift-2)

Explanation

The trait skips generations, as seen with unaffected parents in Generation I having an affected son in Generation II. This indicates a recessive pattern.
Only males are affected in the pedigree, which strongly suggests an X-linked mode of inheritance.
The trait is passed from unaffected (carrier) mothers to their sons, a classic feature of X-linked recessive inheritance.
There is no male-to-male transmission; the affected father in Generation II has an unaffected son, which is a hallmark of X-linked traits.

Option A: This pattern is incorrect because the trait skips generations. Dominant traits typically appear in every generation, and an affected individual must have at least one affected parent.
Option B: This pattern is less likely because only males are affected. Autosomal traits are not linked to sex chromosomes and usually affect both sexes with similar frequency.
Option D: This is incorrect because the trait skips generations. Also, in X-linked dominant inheritance, an affected father would pass the trait to all of his daughters, which is not observed here.

Visual 1: Flowchart - A flowchart guiding the step-by-step analysis of a pedigree chart. Steps would include: 1. Check for dominant vs. recessive pattern (skips generations?). 2. Check for autosomal vs. X-linked pattern (sex bias?). 3. Look for confirmatory evidence (e.g., male-to-male transmission).

Clinical Relevance

Nursing practice connection: Knowing Pedigree analysis and modes of genetic inheritance helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Pedigree analysis is a fundamental, non-invasive tool in genetic counseling to assess the risk of family members inheriting a genetic disorder.
Understanding the mode of inheritance helps in predicting recurrence risks for future offspring and informs decisions about genetic testing for carrier status.
Many well-known genetic conditions follow this X-linked recessive pattern, including Hemophilia A, Duchenne muscular dystrophy, and red-green color blindness.

How to Approach the Question

First, examine the pedigree to see if the trait appears in every generation or skips generations. In this chart, unaffected parents have affected children, which indicates the trait is recessive.
Next, observe the distribution of the trait between sexes. Here, only males are affected, which is a strong clue for X-linked inheritance.
Check for key exclusionary patterns. Look for male-to-male transmission. Since an affected father (Gen II) has an unaffected son, this is consistent with X-linked inheritance.
Synthesize the clues: The combination of a recessive pattern (skips generations) and a strong male bias (only males affected) points directly to X-linked recessive inheritance.

Concept Tested & Keywords

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