Trisomy 23, as a specific condition, does not exist in humans. Humans have 23 pairs of chromosomes, totaling 46. A trisomy, in general, refers to a condition where a person has an extra copy of a chromosome, resulting in 47 chromosomes instead of the usual 46. Therefore, while the question asks about "trisomy 23", it's not a defined medical term because trisomies are named for the specific chromosome that is present in three copies.
Here's what we know about trisomies in general:
- Chromosomes and Trisomy: Humans normally have 23 pairs of chromosomes, for a total of 46, with one set inherited from each parent. Trisomy refers to the presence of an additional chromosome, making a total of 47.
- The Reference's Definition: The reference text clearly states that a trisomy is "a chromosomal condition characterised by an additional chromosome." This results in individuals having 47 chromosomes instead of 46.
- Common Trisomies: The provided reference lists common trisomies including:
- Down syndrome (Trisomy 21)
- Edward syndrome (Trisomy 18)
- Patau syndrome (Trisomy 13)
It is important to understand that there isn't a specific chromosome designated as the 23rd in the sense that adding an extra copy is a known, viable human condition. The 23rd pair determines sex, either XX (female) or XY (male), and a change in these sex chromosomes can lead to different conditions but not typically a "trisomy 23". The term "trisomy" is used for the other 22 chromosome pairs (autosomes), not the 23rd pair (sex chromosomes).
Key points to consider
- No known human condition is designated "trisomy 23"; trisomies are usually defined by the specific autosome that is in triplicate, such as trisomy 21, 18, or 13.
- Trisomy, in general, involves an extra copy of any chromosome, resulting in 47 chromosomes.
- The 23rd chromosome pair are the sex chromosomes, changes in their number or structure lead to sex-chromosome disorders and are not referred to as classic trisomies.
In summary, while the term "trisomy" refers to the presence of an extra chromosome, trisomy 23 is not a recognized medical term for a human condition. Instead, the term trisomy is used with the numbered autosomes.
