NORCET 3 - 2022 (Shif…: In the following human pedigree, the filled symbols represent the affected individuals. Identify the type of…

NORCET 3 - 2022 (Shift-2)

Pathology & Genetics

Hard

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

Explanation

The trait skips generations (e.g., unaffected parents in generation I have an affected son), which is a hallmark of a recessive disorder.
All affected individuals are males, which strongly suggests an X-linked pattern of inheritance over an autosomal one.
There is no male-to-male transmission observed in the pedigree. Affected fathers cannot pass an X-linked trait to their sons.
The pattern is consistent with carrier females (who are phenotypically unaffected) passing the trait to their sons. For example, the female in generation I must be a carrier.

Option A: Autosomal dominant inheritance is incorrect because the trait skips generations. In dominant inheritance, the trait typically appears in every generation, and every affected person has an affected parent.
Option B: Autosomal recessive inheritance is incorrect because although the trait skips generations, it exclusively affects males in this pedigree. Autosomal traits are expected to affect both sexes with similar frequency.
Option D: X-linked dominant inheritance is incorrect because the trait is recessive (it skips generations). Also, in X-linked dominant patterns, an affected father would pass the trait to all of his daughters, which is not seen here (the affected male in generation II has an unaffected daughter).

Clinical Relevance

Nursing practice connection: Knowing Identification of inheritance patterns from a pedigree chart 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. It helps in identifying individuals and families at risk for genetic disorders.
Nurses can use this knowledge to explain inheritance patterns to families, helping them understand the probability of passing a condition to their children.
A nurse obtaining a family history must be systematic and use standardized symbols to create an accurate pedigree, which is a vital tool for diagnosis and management planning.

How to Approach the Question

First, observe the symbols: squares are males, circles are females, and filled symbols represent affected individuals.
Second, determine if the trait is dominant or recessive by checking if it skips generations. If unaffected parents have an affected child, the trait is recessive.
Third, determine if the trait is autosomal or X-linked. Check the sex distribution. If it affects one sex much more than the other (especially males), suspect X-linked inheritance.
Fourth, confirm X-linked inheritance by looking for male-to-male transmission. If an affected father has an unaffected son, it supports X-linked inheritance (and rules out Y-linked). If he has an affected son, it rules out X-linked inheritance.
Finally, synthesize these observations to select the correct inheritance pattern from the given options.

Concept Tested & Keywords

QlTwDKgRaVHWQ5tZVNrfhw

E6 Medicine Harrison 22e Part 2 p. 1695-1697

E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 671-673

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 779-781