Ploidy

Ploidy is the number of complete chromosome sets in a cell or organism. It distinguishes states such as haploidy and diploidy, regardless of the number of chromosomes within each set.

Chromosome: A DNA molecule, together with associated proteins, that carries genetic information in a cell. Ploidy counts complete sets of these structures.
Mitosis: Cell division that usually produces two daughter cells with the same chromosome-set number as the parent. It generally preserves ploidy across ordinary cell divisions.
Polyploidy: The condition of having more than two complete chromosome sets. It is a widespread ploidy state in plants and a tool in crop improvement.
Chromosome number: The count of individual chromosomes in a cell or organism. A chromosome count can vary without changing the number of complete sets.
Human chromosome number: The standard human somatic-cell complement of 46 chromosomes, arranged in 23 pairs. It illustrates diploidy as two sets of 23 chromosomes.
Homologous chromosome: One of a pair of chromosomes with corresponding genes, typically inherited one from each parent. Homologous pairs are the defining feature of diploid cells.
Fertilization: The fusion of gametes to form a zygote. Fusion of haploid gametes usually restores diploidy.
Aneuploidy: An abnormal number of individual chromosomes, rather than a change in complete chromosome sets. It contrasts with ploidy changes, which concern whole sets.
Genome size: The amount of DNA in a haploid genome, often measured in base pairs or mass. Genome size measures DNA quantity, not the number of chromosome sets.
Haplodiploidy: A sex-determination system in which males develop from unfertilized haploid eggs and females from fertilized diploid eggs. It links ploidy directly to sex determination in some insects.

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