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In Ascomycetes and Basidiomycetes, plasmogamy may not be followed immediately by karyogamy. An intervening dikaryotic stage with two nuclei per cell, written as n + n, occurs and is called the dikaryophase.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Phycomycetes Ascomycetes Basidiomycetes
In typical fungal sexual cycle, plasmogamy brings haploid nuclei of compatible mating types into shared cytoplasm creating heterokaryotic or dikaryotic mycelium after hyphal anastomosis. Immediate next phase without nuclear fusion is proliferation of dikaryotic cells via synchronized division, often aided by clamp connections in basidiomycetes ensuring both nuclei segregate. This dikaryotic stage persists extended, with two nuclei dividing conjugately for long periods. Diploid stage only transient after karyogamy inside zygote, ascus or basidium before meiosis. Thus stage directly following plasmogamy is dikaryotic, not diploid, haploid or meiotic.
Ref: Campbell Biology 12th ed., Chapter 31: Fungal Sexual Reproduction Sequence Dikaryotic Stage; NCERT Class 11 Plasmogamy
Dikaryotic stage contains two genetically distinct haploid nuclei per cell, often from different mating types, coexisting without fusion dividing synchronously. Genetically represented as n + n to emphasize paired unfused nuclei versus diploid 2n where chromosomes share nucleus after karyogamy. In Ascomycota dikaryon confined to ascogenous hyphae and asci, in Basidiomycota extensively prolonged forming dominant mycelium producing basidiocarps and clamp connections. This notation clarifies nuclear condition, important for understanding life cycle dominance, heterosis and outcrossing advantages. Haploid denoted n, triploid 3n incorrect here.
Ref: Campbell Biology 12th ed., Chapter 31: Dikaryon n+n Notation; NCERT Class 11 Fungi Dikaryophase; NCBI: Dikaryotic Genetics
In some fungi, karyogamy (nuclear fusion) immediately follows plasmogamy. However, the NCERT textbook explicitly highlights that in Ascomycetes and Basidiomycetes, an extended intervening 'dikaryotic stage' occurs. In this fascinating phase, a single cell contains two distinct haploid nuclei (n + n), a condition termed a dikaryon. The parental nuclei fuse much later to eventually form a diploid cell before meiosis occurs.
Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.3 Kingdom Fungi
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