triploïd

Triploïd refers to an organism or cell with three complete sets of chromosomes (3n). In most sexually reproducing organisms, somatic cells are diploid (2n) and gametes are haploid (n). Triploidy arises when a triploid zygote is formed by fertilization involving an unreduced gamete (2n) and a normal haploid gamete, or by interspecific hybridization. Triploidy can result from errors in meiosis, from endoreduplication, or from crosses between different species, leading to genomes combining three chromosome sets. Two main genetic routes are autopolyploidy (three sets from the same species) and allopolyploidy (three sets from different species), although most real-world triploids involve a combination of these processes.

In plants, triploids are relatively common and are often sterile because the three homologous chromosome sets fail to pair evenly during meiosis, limiting seed production. This sterility is exploited commercially to produce seedless fruits such as some watermelons, bananas, and grapes. Triploids can still propagate vegetatively or through asexual means.

In animals and humans, triploidy is usually lethal. In humans, triploidy occurs in a small fraction of conceptions and most pregnancies end in miscarriage; rare partial or mosaic triploidy can be associated with severe developmental abnormalities in live births or neonatal death.

Detection and study of triploidy involve cytogenetic karyotyping, flow cytometry to assess DNA content, and molecular genetic methods. Triploidy illustrates how deviations from the normal diploid genome can influence development, fertility, and agricultural practices.