Aneuploidy is an abnormality in the number of chromosomes in a cell due to loss or duplication.
Understanding Aneuploidy
In simple terms, aneuploidy refers to a genetic condition where a cell has too many or too few chromosomes compared to the normal count for that species.
The Normal Chromosome Count
Most human cells contain 46 chromosomes, organized into 23 pairs (22 pairs of autosomes and 1 pair of sex chromosomes). This is the standard or 'euploid' state.
How Aneuploidy Occurs
Aneuploidy arises when there is a problem during cell division, leading to chromosomes being lost or duplicated. This means the resulting cell does not have the usual, correct number of chromosomes.
As stated in the reference, in humans, aneuploidy would be any number of chromosomes other than the usual 46. This deviation from the standard count can have significant effects.
Common Examples of Aneuploidy
The most common forms of aneuploidy involve the gain or loss of a single chromosome:
- Trisomy: Having an extra copy of a chromosome (totaling 3 instead of the usual 2).
- Monosomy: Missing one copy of a chromosome (totaling 1 instead of the usual 2).
Some well-known examples of aneuploidy in humans include:
- Down syndrome (Trisomy 21 - an extra copy of chromosome 21)
- Edwards syndrome (Trisomy 18 - an extra copy of chromosome 18)
- Patau syndrome (Trisomy 13 - an extra copy of chromosome 13)
- Turner syndrome (Monosomy X - missing one X chromosome)
- Klinefelter syndrome (XXY - an extra X chromosome in males)
Types of Aneuploidy
Aneuploidy can involve any chromosome and can be classified based on the number of missing or extra copies.
| Type | Description | Chromosome Count (Human Example) |
|---|---|---|
| Nullisomy | Loss of both chromosomes | 44 |
| Monosomy | Loss of one chromosome | 45 |
| Trisomy | Gain of one chromosome | 47 |
| Tetrasomy | Gain of two chromosomes | 48 |
Understanding aneuploidy is crucial in genetics and medicine, particularly in the context of developmental disorders and reproductive health.
