Vegetative cells usually are haploid, and reproduce asexually by division into two, or some small multiple of two, progeny cells. Under certain conditions, usually involving induction of vegetative cell growth under nitrogen limitation, vegetative cells divide to form gametes. Gametes look like vegetative cells, but have differentiated mating structures near their apices. Cysts are usually diploid, form by fusion of gametes. Meiosis in the cysts usually yields four vegetative cells. This cycle is easy to manipulate under controlled culture conditions. Morphological species frequently can be crossed in the laboratory.
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