**Core Concept**
The question refers to a specific chromosomal abnormality that results from the duplication of a segment of a chromosome. This phenomenon occurs when there is a non-disjunction event during meiosis, leading to an extra copy of a particular chromosomal segment.

**Why the Correct Answer is Right**
The correct chromosomal abnormality is characterized by the presence of an extra copy of a segment of chromosome 21. This condition arises due to a translocation event where the long arm of chromosome 21 breaks off and attaches to another chromosome, typically chromosome 14. This abnormality leads to an increased risk of genetic disorders, including Down syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not describe a specific chromosomal abnormality resulting from a segment duplication.
* **Option B:** This option is incorrect because it refers to a different chromosomal abnormality, specifically a deletion of a segment of chromosome 5.
* **Option C:** This option is incorrect because it describes a different type of chromosomal abnormality, specifically a Robertsonian translocation.

**Clinical Pearl / High-Yield Fact**
The chromosomal abnormality in question is associated with a characteristic facial appearance, intellectual disability, and an increased risk of congenital heart defects. It is essential for clinicians to recognize the signs and symptoms of this condition to provide appropriate care and management.

**Correct Answer: D. Trisomy 21**