Introduction to Sexual Sporulation

Life cycle of a primitive unicellular organism:
Life cycle of a primitive unicellular organism.
  • The basic life cycle of a primitive unicellular organism may have consisted of two phases - HAPLOID and DIPLOID.
  • Such an organism may have increased in complexity and evolved into a multicellular organism in either the haploid or the diploid phase.
Life cycle of higher plants and animals:
Life cycle of higher plants and animals.
  • In higher plants and animals (e.g. humans) the somatic multicellular organism is DIPLOID.
  • MEIOSIS is involved in the formation of HAPLOID GAMETES.
  • NUCLEAR FUSION following the union of two gametes returns us to the DIPLOID state.
Life cycle of fungi belonging to the Oomycota:
Life cycle of Oomycota fungi.
  • In species belonging to the Oomycota,  nuclei in the somatic (vegetative) hyphae are DIPLOID.
  • ASEXUAL SPORULATION, therefore, results in the formation of DIPLOID ZOOSPORES.
  • SEXUAL SPORULATION involves the formation of specialised reproductive structures in which MEIOSIS results in the fomation of HAPLOID GAMETES.
  • The FUSION of compatible gametes is a preliminary to the formation of DIPLOID OOSPORES which germinate and return us to the DIPLOID SOMATIC PHASE.
Life cycle of other fungi (excluding the Oomycota):
Life cycle of fungi (excluding Oomycota).
  • In fungi (excluding the Oomycota), the somatic hyphae are HAPLOID.
  • FUSION OF TWO HAPLOID GAMETES leads to formation of a DIPLOID ZYGOTE.
  • MEIOSIS returns us to the HAPLOID state.

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