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Genetics of Fungi.docx

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Western University
Biology 4218A
Richard Gardiner

Genetics of Fungi Advantages of Fungi for genetics - Haploid  easy to get mutants and mutate (Oomycetes  diploid) - Convenience factors (size, cost, rapid life cycles) - Heterokaryons, Dikaryons and diploid stages available - Analysis of individual meiosis possible, easy to analyze mitotic recombination Sex and mating type - Wide range of gamete types (isogamy to anisogamy) - Homothallism: one strain sufficient for sexual development - Heterothallism: two strains needed for sexual development (opposite mates) - Secondary homothallism: separate mating types (sexual spores formed with both present) - Vegetative incompatibility groups (VCG) can prevent fusion of vegetative hyphae  block sexual reproduction Mating type systems 1. Bipolar: involves 1 locus with 2 to many alleles 2. Tetrapolar: involve 2 loci each with 2 to many alleles (distinct functions) Example: A2B3 can mate with A1B5 (must be different at both A and B for full mating) Analysis of a new fungus 1. Isolate mutants a. Mutagenize b. Select mutants (devise screen i.e. plate on drug containing medium for drug resistance) c. Identify mutant if necessary (i.e. what growth factor does nutritional mutant need?) Selecting and identifying mutants o Auxotrophs 2. Test for dominance: check by combining with wild type allele in diploid or Dikaryons a. If phenotype is mutant then mutant is dominant; if WT then recessive 3. Test for Allelism a. If have 10 mutants with similar phenotype, are all mutant in same gene? b. Biochemical test – check ability to grow when given precursors of growth factors c. Complementation test – check ability of 2 similar mutants to give WT when combined in diploid/Dikaryons - Start mapping genes. Can map via: o Sexual cycle – analysis of meiosis (random spore analysis + tetrad)  Random spore analysis  Tetrad analysis (Ascomycetes keep all products of one meiosis inside Ascus  can analyze them as a group)
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