Diploid

Diploid refers to cells or organisms that contain two complete sets of chromosomes (2n). In most eukaryotes, these are two homologous chromosome sets, one inherited from each parent. The two homologs carry the same genes in the same order, but may contain different alleles.

In animals and many plants, somatic cells are diploid, whereas gametes are haploid (n). Fertilization joins two haploid gametes to form a diploid zygote, restoring the 2n chromosome number.

The diploid state is maintained by mitotic cell division, in which a cell duplicates its chromosomes and then divides to yield two genetically identical diploid daughter cells.

Meiosis is a special diploid-reducing division that produces haploid gametes and increases genetic diversity through synapsis and crossing over.

Exceptions and variation: some somatic tissues are polyploid (having more than two chromosome sets), notably in plants and in liver or muscle of some animals; other organisms can be haploid throughout life or alternate ploidy during development.

Importance: ploidy level affects inheritance patterns, gene expression, and evolution; diploidy allows recessive alleles to persist hidden.