**Core Concept**
Trisomy refers to a genetic disorder caused by the presence of an extra copy of a chromosome, resulting in an abnormal number of chromosomes in an individual's cells. This condition can lead to various developmental and congenital abnormalities.

**Why the Correct Answer is Right**
Trisomy occurs when there is a non-disjunction event during meiosis, where the genetic material fails to separate properly, resulting in an extra copy of a chromosome. This can occur in any chromosome, but it is most commonly seen in chromosomes 21 (Down syndrome), 13 (Patau syndrome), 18 (Edwards syndrome), and 16 (Pallister-Killian syndrome). The presence of an extra chromosome can disrupt the balance of genetic material, leading to developmental abnormalities and increased risk of congenital defects.

**Why Each Wrong Option is Incorrect**
* **Option A:** Not a known association with trisomy.
* **Option B:** Not a recognized genetic disorder related to trisomy.
* **Option D:** Not a known association with trisomy.

**Clinical Pearl / High-Yield Fact**
Trisomy can be detected prenatally through amniocentesis or chorionic villus sampling, allowing for early diagnosis and informed decision-making regarding pregnancy continuation.

**Correct Answer: C. Trisomy 21 (Down syndrome) is the most common form of trisomy, accounting for approximately 50% of cases.**