Identify the disorder following flow charts (NORCET-2023)

NORCET 2 -2021 (Shift-2)

Pathology & Genetics

Hard

Appeared in: NORCET 2 -2021 (Shift-2)

Explanation

The pedigree demonstrates an X-linked dominant inheritance pattern.
The key feature is the transmission from the affected father in Generation I to all of his daughters in Generation II, and none of his sons. This is a classic sign of X-linked dominant inheritance.
Fathers pass their single X chromosome to all their daughters, so if the gene for a dominant disorder is on the X chromosome, all daughters will be affected.
Fathers pass their Y chromosome to their sons, so there can be no father-to-son transmission of an X-linked trait.
The trait also appears in every generation, which is characteristic of dominant inheritance.

Option A: In autosomal dominant inheritance, an affected father would have a 50% chance of passing the trait to each child, regardless of sex. It is statistically unlikely he would pass it to both daughters and neither of his sons.
Option B: Autosomal recessive disorders typically skip generations, as affected individuals usually have unaffected (carrier) parents. This pedigree shows the trait in every generation.
Option C: X-linked recessive disorders also tend to skip generations and are much more common in males than females. Here, the trait is dominant (seen in every generation) and affects females.

Visual 1: Diagram - A simplified diagram illustrating how an affected father passes his X chromosome to all daughters and Y chromosome to all sons, explaining the X-linked dominant pattern.
Visual 2: Flowchart - A flowchart for pedigree analysis, starting with the question 'Does the trait skip generations?' to differentiate between dominant and recessive, followed by 'Does an affected father pass it to all daughters?' to differentiate between autosomal and X-linked dominant.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pedigree analysis and modes of genetic inheritance as background academic context rather than a clinical decision trigger.
Pedigree analysis is a fundamental tool in genetic counseling for assessing a family's risk of inheriting or passing on a genetic disorder.
Identifying the correct mode of inheritance allows nurses and genetic counselors to provide accurate information about recurrence risks, prognosis, and potential genetic testing options.
What if? If the affected father in Generation I had an affected son, X-linked inheritance would be ruled out, and Autosomal Dominant would become the correct answer, as this would demonstrate male-to-male transmission.

How to Approach the Question

Step 1: Analyze the pedigree for vertical vs. horizontal patterns. Observe if the trait appears in every generation. If yes, it is likely a dominant trait. If it skips generations, it is likely recessive. In this chart, the trait is in every generation, suggesting dominance.
Step 2: Rule out recessive options (Autosomal Recessive, X-linked Recessive) based on the dominant pattern.
Step 3: Differentiate between Autosomal Dominant and X-linked Dominant by checking the offspring of affected males.
Step 4: Look for the key pattern: Does an affected father pass the trait to his sons? If yes, it's Autosomal Dominant. If no, check his daughters. Does he pass it to ALL of his daughters?
Step 5: In this chart, the affected father passes the trait to ALL of his daughters and NONE of his sons. This is the definitive rule for X-linked Dominant inheritance.
Step 6: Select X-linked Dominant as the correct answer based on this conclusive evidence.

Concept Tested & Keywords

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