Ploïdie

Ploïdie refers to the number of complete sets of chromosomes in a cell. Organisms with two complete sets of chromosomes, one from each parent, are called diploid. Most animals and many plants are diploid. Organisms with only one complete set of chromosomes are called haploid. Gametes, such as sperm and egg cells, are typically haploid.

The term polyploidy describes the condition of having more than two complete sets of chromosomes. For example, a triploid organism has three sets, a tetraploid has four, and so on. Polyploidy is common in plants, where it can lead to larger fruits, flowers, or seeds, and can be a factor in plant speciation. Many staple crops, such as wheat, potatoes, and strawberries, are polyploid.

In animals, polyploidy is much rarer and is often associated with developmental abnormalities or lethality. However, some species, like certain flatworms and fish, are naturally polyploid. Ploïdie can arise through errors during cell division, such as the failure of chromosomes to separate properly during meiosis or mitosis. This can result in gametes with an abnormal number of chromosomes or somatic cells with altered ploidy levels. The study of ploidy is important in genetics, evolutionary biology, and agriculture.