What term describes an organism or cell having only one complete set of chromosomes?

The term that describes an organism or cell having only one complete set of chromosomes is haploid. In a haploid cell, there is a single set of chromosomes, which means that it contains one representative of each chromosome pair found in diploid organisms. This is typical of gametes, such as sperm and egg cells in animals, where they contribute to genetic diversity when they unite during fertilization.

In contrast, diploid refers to cells that contain two complete sets of chromosomes, one inherited from each parent, which is the most common state for somatic cells in many organisms. Triploid cells, which have three complete sets of chromosomes, and tetraploid cells, which have four, are less common and typically arise through specific processes such as failed cell division or hybridization between different species. Understanding the different ploidy levels is essential in genetics and evolutionary biology, as they play significant roles in reproduction and inheritance.