Introduction to Sexual Sporulation
- Life cycle of a primitive unicellular organism:
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- 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:
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- 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:
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- 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):
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- 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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