(1) A phase of development of an organism, characterized by a double, or diploid, set of chromosomes. In higher organisms the diplophase embraces a large part of the life cycle—from the formation of the zygote to the beginning of meiosis, when the gametes are formed and there is a reduction in the number of chromosomes to a single (haploid) set, which is characteristic of the haplophase. In many species (for example, in mosses and algae) the diplophase is represented only by the zygote, in which meiosis occurs and, consequently, transition to the haplophase.

(2) A little-used synonym for diplotene, one of the prophase stages in the first meiotic division.