Aneuploidy refers to a condition where there is an abnormal number of chromosomes in a cell. This means that instead of having the usual two copies of each chromosome (in diploid organisms), there's either an extra copy of a single chromosome (trisomy, like in Down syndrome with an extra copy of chromosome 21) or a missing copy of a single chromosome (monosomy).
Polyploidy, on the other hand, involves having one or more complete sets of chromosomes beyond the standard diploid number. For example, a triploid organism has three sets of chromosomes (3n), and a tetraploid organism has four sets (4n). Polyploidy is common in plants and can lead to larger size and other altered characteristics.
| Feature | Aneuploidy | Polyploidy |
|---|---|---|
| Definition | Presence of an abnormal number of individual chromosomes. | Presence of one or more complete extra sets of chromosomes. |
| Chromosome Number | $2n ± x$ (where x is the number of chromosomes gained or lost) | $3n, 4n, 5n,$ etc. (where n is the haploid number) |
| Examples | Down syndrome (Trisomy 21), Turner syndrome (Monosomy X) | Many crop plants (e.g., wheat, potatoes) |
| Viability | Often leads to developmental abnormalities or lethality, especially in animals. | More common and better tolerated in plants; can lead to increased size and vigor. |
| Cause | Nondisjunction during meiosis. | Errors in cell division, such as failure of cytokinesis after chromosome duplication. |
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