**Core Concept**
Chromosomal non-disjunction is a fundamental concept in genetics that refers to the failure of chromosome pairs to separate properly during cell division, resulting in an abnormal number of chromosomes in the offspring cell. This can lead to various genetic disorders and conditions.

**Why the Correct Answer is Right**
Chromosomal non-disjunction occurs due to errors in meiosis or mitosis, where the chromosomes fail to separate correctly, leading to aneuploidy. Aneuploidy can result in genetic disorders such as Down syndrome, Turner syndrome, and Klinefelter syndrome. Non-disjunction can occur in any chromosome, but it is more common in certain chromosomes, such as chromosome 21, which is involved in Down syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Down syndrome is a well-documented consequence of chromosomal non-disjunction, specifically involving an extra copy of chromosome 21. Therefore, this option is incorrect.
**Option B:** Turner syndrome is also caused by chromosomal non-disjunction, resulting in a missing X chromosome in females. Thus, this option is incorrect.
**Option C:** Klinefelter syndrome, characterized by an extra X chromosome in males, is another example of a genetic disorder resulting from chromosomal non-disjunction. Therefore, this option is incorrect.
**Option D:** This option is correct because chromosomal non-disjunction is not responsible for all genetic disorders. While it is a common mechanism, other mechanisms such as mutations, deletions, and duplications can also contribute to genetic disorders.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that chromosomal non-disjunction can occur in any cell type, not just gametes, and can result in various genetic disorders. This highlights the importance of genetic counseling and screening for individuals with a family history of genetic disorders.

**Correct Answer:** D.