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Lecture 13

BIO153 Lecture 13.pdf

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Christoph Richter

2009 BIO153: Lecture 13 Life Cthles in Fungi Mar 9 , 2009 Reproduction in Fungi can take many forms – both sexual and asexual. Asexual reproduction: ▯ budding, fission (in unicellular fungi i.e. yeasts) ▯ breakage or fragmentation of the mycelium (multicellular fungi) ▯ asexual sporulation (common in all multicellular fungiexcept Basidiomycota) Sexual reproduction: ▯ conjugation (unicellular fungi – yeasts) ▯ sexual sporulation Sporulation: both sexual and asexual Spores are the key to fungal success. They are light, small, and energetically cheap to produce (e.g. compared to seeds). They are the means by which the fungus disperses. ▯ spores are always haploid ▯ when fungal spores germinate, they divide mitotically to produce a haploid mycelium ▯ asexual spores are produced by mitosis; sexual spores are produced by meiosis ▯ spores are produced in huge numbers ▯ they are light, resistant to desiccation, & can remain dormant for years until conditions for germination are right ▯ the onset of sporulation (both sexual and asexual) is triggered by seasonal cues, nutrient levels, light, CO … 2 Life cycles in fungi: Chytridiomycota: ▯ basal group: have a different life cycle from other fungi ▯ true alternation of generations (multicellular diploid and haploid structures): Type III life cycle ▯ aquatic: motile gametes and spores (gametes fuse to produce a zygote which forms a multicellular sporophyte – just like a plant!) ▯ no dikaryon 1 Other than Chytridiomycota: A generalized fungal life cycle (a variation on the Type I life cycle): Most fungi have both a sexual and asexual part of the life cycle. 1. Asexual cycle: ▯ common in most fungi (except Basidiomycota) ▯ haploid spores (conidia) are formed by mitosis in haploid hyphae ▯ germination of asexual spores ▯ haploid hyphae ▯ conidia: asexual spores ▯ medically important: estimated that people inhale ~40 conidia per hour; can result in opportunistic fungal infections (e.g. in HIV+ patients) deuteromycota: fungi imperfecta ▯ imperfecta = no sexual cycle has been observed; only asexual sporulation ▯ not a true taxonomic group 2 2. Sexual cycle The sexual cycle in mo
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