**Core Concept**
Chromosomal non-disjunction is a fundamental concept in genetics where the normal process of chromosome separation during cell division fails, leading to an abnormal number of chromosomes in the daughter cells. This genetic anomaly can result in various conditions, including aneuploidy, which is a condition where an individual has an abnormal number of chromosomes.

**Why the Correct Answer is Right**
Chromosomal non-disjunction can occur during meiosis or mitosis, and it is responsible for several genetic disorders, including Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). These conditions are caused by the presence of an extra copy of a particular chromosome, leading to an imbalance in gene expression and protein production. The mechanism of chromosomal non-disjunction involves errors in the separation of chromosomes during cell division, which can be caused by various factors, including age, environmental exposures, and genetic mutations.

**Why Each Wrong Option is Incorrect**
* **Option A:** Chromosomal translocations, while related to genetic anomalies, are not caused by chromosomal non-disjunction. Chromosomal translocations involve the exchange of genetic material between non-homologous chromosomes.
* **Option B:** Mitochondrial disorders are not directly caused by chromosomal non-disjunction. Mitochondrial disorders result from mutations in mitochondrial DNA, which is separate from the nuclear DNA that is affected by chromosomal non-disjunction.
* **Option C:** Somatic mosaicism is a condition where some cells in the body have a chromosomal abnormality, while others do not. While somatic mosaicism can be caused by chromosomal non-disjunction, it is not the only possible cause.

**Clinical Pearl / High-Yield Fact**
Chromosomal non-disjunction is a common cause of genetic disorders in older mothers, and the risk of chromosomal abnormalities increases with maternal age.

**Correct Answer: D.**