Aneuploidy and polyploidy are both conditions involving abnormal chromosome numbers, but they differ significantly in the type of chromosomal change.
Understanding Chromosome Number Variations
Here's a breakdown of each condition, highlighting the key differences:
| Feature | Aneuploidy | Polyploidy |
|---|---|---|
| Definition | Presence of one or a few missing or extra individual chromosomes. | Presence of one or more extra complete sets of chromosomes. |
| Change Type | Partial change in chromosome number | Complete change in chromosome set number |
| Examples | Trisomy 21 (Down syndrome), Turner syndrome | Triploidy, Tetraploidy |
Aneuploidy
- Definition: Aneuploidy occurs when a cell has an abnormal number of individual chromosomes. This means there is either a loss (monosomy, where one chromosome is missing from a pair) or a gain (trisomy, where one extra chromosome is present) of one or a few chromosomes.
- Example: Trisomy 21, where an individual has three copies of chromosome 21 instead of the normal two, leading to Down Syndrome. Another example is Turner syndrome where a female has only one X chromosome instead of two.
- Cause: Aneuploidy is most often caused by errors during cell division, specifically during meiosis (the process that forms egg and sperm cells), called nondisjunction.
Polyploidy
- Definition: Polyploidy is characterized by the presence of extra full sets of chromosomes in a cell. Instead of just one extra chromosome, there are multiple copies of the entire chromosome set, exceeding the usual diploid state (two sets).
- Example: A diploid human cell has 2 sets of 23 chromosomes, for a total of 46. A triploid cell (3n) will have three copies of each chromosome set, for a total of 69 chromosomes. A tetraploid cell (4n) will have four sets of chromosomes, for a total of 92.
- Cause: Polyploidy arises from mistakes in cell division, such as the failure of chromosomes to separate during meiosis or mitosis, which can lead to cells containing more than two sets of chromosomes. It is relatively common in plants, leading to new species, but is rare and typically not viable in animals.
Key Differences Summarized
In essence, the key distinction lies in the scale of the chromosomal change:
- Aneuploidy deals with gains or losses of single chromosomes, creating an imbalance in a pair or group.
- Polyploidy results in gains of entire chromosome sets, where the balance within a set is maintained, although there are additional copies of the whole set.
Reference: Aneuploidy is the phenomenon in which a cell can have one or a couple of chromosomes missing or present in surplus. On the other hand, polyploidy refers to the presence of extra complete sets of chromosomes.
