Identify the following disorder in pedigree flowchart?

NORCET 5 mains

Pathology & Genetics

Medium

Appeared in: NORCET 5 mains

Explanation

The pedigree displays the classic hallmark of X-linked dominant inheritance.
The affected father in Generation I passes the trait to all of his daughters in Generation II.
The affected father does not pass the trait to any of his sons, as they inherit his Y chromosome, not his X chromosome.
In X-linked dominant traits, a single copy of the mutated gene on the X chromosome is sufficient to cause the disorder.

Option A: In autosomal dominant inheritance, an affected father would have a 50% chance of passing the trait to each child, regardless of their sex. It would not selectively affect all daughters and no sons.
Option B: Autosomal recessive disorders typically skip generations, and affected individuals are often born to unaffected carrier parents. Here, the father is affected, and the trait appears in consecutive generations.
Option C: In X-linked recessive inheritance, an affected father would pass the recessive allele to all his daughters, making them obligate carriers but phenotypically unaffected (assuming the mother is not a carrier). The pedigree shows the daughters are affected.

Visual 1: Diagram - A Punnett square illustrating X-linked dominant inheritance from an affected father (X'Y) and an unaffected mother (XX), showing that 100% of female offspring (X'X) are affected and 100% of male offspring (XY) are unaffected.
Visual 2: Flowchart - A flowchart detailing the steps to analyze a pedigree: 1. Check for mitochondrial inheritance (maternal line only). 2. Check if it skips generations (suggests recessive). 3. Check for sex bias (suggests X-linked). 4. Confirm with specific parent-child transmissions (e.g., father-to-son rules out X-linked).

Clinical Relevance

Nursing practice connection: Knowing Pedigree Analysis and Modes of Inheritance helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding pedigree analysis is crucial for nurses in genetic counseling, risk assessment, and patient education.
Identifying the mode of inheritance helps predict the risk of recurrence in future pregnancies and for other family members.
Examples of X-linked dominant disorders include Fragile X syndrome, Rett syndrome, and Alport syndrome.

How to Approach the Question

First, observe the overall pattern in the pedigree. Note if the trait appears in every generation (suggesting a dominant trait) or skips generations (suggesting a recessive trait). In this case, it is in every generation.
Next, check for sex-specific patterns. See if the trait affects males and females equally or if there is a clear bias.
Focus on key transmissions. The most telling clue here is the affected father in Generation I. Trace the inheritance to his children.
Analyze the father's offspring: All his daughters are affected, and all his sons are unaffected.
Test this observation against the rules of inheritance. The rule 'affected father passes the trait to all daughters and no sons' uniquely identifies X-linked dominant inheritance.
Eliminate other options based on this key finding. For example, the absence of father-to-son transmission rules out autosomal inheritance as the sole explanation for this specific pattern.

Concept Tested & Keywords

Concept Tested: Pedigree Analysis and Modes of Inheritance
Stem keywords: pedigree flowchart, disorder, inheritance
Lead-in keywords: Identify
Clinical cues: Affected father with all daughters affected and all sons unaffected is a key clinical cue.

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