Triploids

Triploids are organisms that possess three complete sets of chromosomes, or 3n. They arise when two haploid gametes fuse with an unreduced gamete (2n) or when a diploid and a tetraploid parent contribute, or through hybridization between species with different ploidy levels. Triploidy is a form of polyploidy and can be autopolyploid (from the same species) or allopolyploid (from different species).

In plants, triploidy is relatively common and often results in sterility due to problems during meiosis when three homologous chromosomes cannot pair evenly. This sterility is advantageous in agriculture for producing seedless fruits. Seedless watermelon, some triploid citrus varieties, and various seedless grapes are cultivated examples. Triploids can exhibit vigor or larger cell size, but may have reduced fertility and altered growth traits relative to diploids.

In animals, triploidy is rarer and many triploid individuals are sterile. In aquaculture, triploidy is intentionally induced to produce sterile fish or shellfish, reducing the risk of interbreeding with wild populations and controlling reproduction. Common methods include inducing triploidy in fertilized eggs through heat or pressure shocks to disrupt normal meiosis.

Genetically, triploidy disrupts balanced chromosomal pairing, yielding unbalanced gametes and reduced fertility. Some triploids can reproduce asexually or produce limited, mostly nonviable offspring. Detection and confirmation of triploidy are achieved through cytogenetic analysis or DNA-based genome size measurements.