Why dikaryotic phase is found in fungi
Answers
Answer:
Sexual reproduction in Fungus involves the formation and the union of two gametes or their nuclei. Sexual reproduction is absent in the artificial group of fungi called Fungi imperfecti or Deuteromycetes. Depending upon the compatibility in sexual reproduction, fungi are of two types_ Homothallic and Heterothallic.
In Heterothallic forms sexual reproduction involves fusion between two genetically different mating types. In Homothallic forms fusion occurs between genetically similar types. Fusion involves the union of cytoplasms as well as nuclei. The former is called Plasmogamy while the latter is called Karyogamy.
In higher fungi, karyogamy is delayed and occurs just before meiosis. In the stage intervening between plasmogamy and karyogamy the cells often contain two nuclei or Dikaryons (n+n). Such cells are called dikaryotic cells. The phase is known as Dikaryophase which takes place in Ascomycetes and Basidiomycetes.
In such fungi life cycle is completed in three phases instead of two_ Haplophase, Dikaryophase and Diplophase (2n). Meiosis occurs in diplophase.
So the correct option is 'Ascomycetes and Basidiomycetes'.
Answer: In the life cycle of a sexually reproducing fungus, a haploid phase alternates with a diploid phase. The haploid phase ends with nuclear fusion, and the diploid phase begins with the formation of the zygote (the diploid cell resulting from fusion of two haploid sex cells). Meiosis (reduction division) restores the haploid number of chromosomes and initiates the haploid phase, which produces the gametes. In the majority of fungi, all structures are haploid except the zygote. Nuclear fusion takes place at the time of zygote formation, and meiosis follows immediately. Only in Allomyces and a few related genera and in some yeasts is alternation of a haploid thallus with a diploid thallus definitely known.
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