Biology · Biological Classification · NEET
A dikaryon is NEITHER truly haploid nor diploid — it is a special stage called dikaryotic. It has two SEPARATE haploid nuclei (n and n) inside one cell. The total DNA amount looks like 2n, but the two nuclei have NOT fused, so it is written n+n, not 2n. A real 2n (diploid) cell has ONE nucleus made by fusing both. NEET loves testing this exact difference.
Because the two haploid nuclei stay separate. In 2n, the two sets of chromosomes are inside ONE nucleus after karyogamy (nuclear fusion). In n+n, they are still in TWO different nuclei sitting side by side. The '+' sign means 'together but not merged'. Remember: n+n = two nuclei, 2n = one fused nucleus.
It comes AFTER plasmogamy but BEFORE karyogamy. Order: (1) Plasmogamy = cytoplasms fuse, so two nuclei now share one cell → this makes the dikaryon (n+n). (2) The dikaryophase can last a long time. (3) Karyogamy = the two nuclei finally fuse → now the cell is diploid (2n). So dikaryon is the 'waiting stage' between the two fusions.
Mainly Ascomycetes (sac fungi like Aspergillus, Penicillium, Neurospora) and Basidiomycetes (club fungi like Agaricus, Puccinia, Ustilago). In many other fungi (like Phycomycetes), the two haploid cells fuse and the nuclei fuse IMMEDIATELY, so there is no long dikaryon stage. NCERT names these two classes directly — expect a question on it.
Dikaryon is the CELL or structure that contains the two separate nuclei (n+n). Dikaryophase is the PHASE (period of time) in the fungus life cycle when this dikaryotic condition exists. Simply: dikaryon = the thing, dikaryophase = the stage. Both come from the same event (plasmogamy without immediate karyogamy).
In Ascomycetes and Basidiomycetes the dikaryon can last a LONG time — the fungus can even grow a whole mycelium and fruiting body in the n+n condition. Only later, inside the ascus or basidium, does karyogamy happen. This delay is exactly why these fungi are famous for their dikaryophase.
Match List-I with List-II: List-I: A. Fusion of protoplasms between gametes B. Fusion of two nuclei C. Generation of haploid spores List-II: I. Meiosis II. Plasmogamy III. Karyogamy Choose the correct answer:
After karyogamy followed by meiosis, spores are produced exogenously in
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A fungal cell that has two separate haploid nuclei (n+n) living together but not yet fused into one.
Neither — it is dikaryotic. Two haploid nuclei stay separate, so we write n+n, not 2n. It becomes diploid only after karyogamy.
Mainly in Ascomycetes and Basidiomycetes. In these classes an intervening n+n dikaryon stage occurs before nuclear fusion.
Plasmogamy is fusion of cytoplasm (makes the dikaryon n+n). Karyogamy is fusion of the two nuclei (makes it diploid 2n).
NEET tests the sequence plasmogamy → dikaryon (n+n) → karyogamy → meiosis, and the fact that n+n is not the same as 2n.
