The parasexual cycle is defined as a cycle in which plasmogamy, karyogamy and meiosis take place but not at a specified time or at specified points in the life cycle of an organism. The members of class Deuteromycetes in which sexual cycle does not occur, exhibit parasexual cycle generally.
It was first discovered by Pontecarvo and Roper of University of Glasgow (1952) in Aspergillus nidulans, the imperfect stage of Embericella nidulans.
Steps :1. Formation of heterokaryotic mycelium
2. Karyogamy: Fusion between two nuclei
a) Fusion between like nuclei
b) Fusion between unlike nuclei
3. Multiplication of diploid nuclei
4. Occasional mitotic crossing over
5. Sorting out of diploid nuclei.
6. Occasional haploidisation of diploid nuclei
7. Sorting of new haploid strains
New and better strains of fungi(Deuteromycetes) are obtained by mutation through parasexual cycle.