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The fungal sexual cycle involves plasmogamy, the fusion of protoplasms; karyogamy, the fusion of nuclei; and meiosis in the zygote, which produces haploid spores.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Bacteria - Structure and Economic Importance
Most fungal life cycles are haplontic with predominant stage haploid performing growth, foraging and ecological functions. Vegetative mycelium, which performs nutrient absorption and colonization, carries haploid nuclei throughout except transient diploid zygote. Diploid phase restricted to fleeting zygote formed after karyogamy within ascus, basidium or zygosporangium, immediately undergoing meiosis to regenerate haploid spores ensuring genetic diversity. No alternation favoring diploid dominance as in animals or diplontic algae. Triploid and tetraploid uncommon except lab-induced heterokaryosis. Haploid dominance facilitates rapid expression of beneficial mutations and adaptation.
Ref: Campbell Biology 12th ed., Chapter 31: Fungal Life Cycle Haploid Dominant; NCERT Class 12 Genetics - Fungal Dominance; NCBI Haplontic Cycle
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
Fungal sexual cycle comprises orderly sequence: plasmogamy, karyogamy, meiosis precisely regulated by mating-type loci. Plasmogamy denotes fusion of cytoplasm from two compatible parental mycelia bringing haploid nuclei together in same cell without nuclear fusion. Occurs after anastomosis between hyphae of opposite mating types determined by MAT genes. Results in dikaryotic or heterokaryotic stage containing genetically distinct nuclei. Distinguished from karyogamy which fuses nuclei into diploid, meiosis reduces ploidy, mitosis produces clones. Plasmogamy therefore represents initial cytoplasmic union enabling subsequent recombination.
Ref: Campbell Biology 12th ed., Chapter 31: Fungal Life Cycles Plasmogamy; NCERT Class 11 Fungi - Sexual Reproduction Steps; NCBI Mycology
