Which term refers to organisms possessing four sets of chromosomes?

The term that refers to organisms possessing four sets of chromosomes is tetraploid. Tetraploidy specifically indicates that the organism has four complete sets of chromosomes, which is often represented as 4n, where n denotes the number of sets of chromosomes in a haploid organism. In many plants and some animal species, tetraploidy can occur due to various processes such as errors in cell division or hybridization events that lead to a doubling of the chromosome sets.

Diploidy refers to organisms with two sets of chromosomes, which is common in many animals, including humans. Euploidy is a broader term that encompasses any organism with a complete set of chromosomes, including diploids and polyploids, but does not specify the exact number of sets. Polyploid, while also indicating organisms with more than two sets of chromosomes, can refer to any number greater than two (like triploid or hexaploid) and thus is not limited to tetraploid organisms specifically. Therefore, tetraploid is the most precise term for organisms with four sets of chromosomes.