Two factors, A/B (mostly basids)

1. Two factors, A/B (mostly basids) • Tetrapolar mating system  meiosis gives four types of segregants • Need different alleles at each mating locus • A1B1 :: A2B2A1B1, A1B2, A2B1, A2B2 • Schizophyllum has ~28,000 mating type combinations

2. Basidiomycete mating • Mating dikaryon formation  fruiting • Mating uses pheromones + receptors that signal through a kinase cascade fruit body for heterobasidiomycetes

3. A and B functions are distinct • in homobasids (.....?) • A controls pairing and synchronous division of nuclei, hook cell formation; • B controls septal dissolution and hook cell fusion (precise b-glucanase activity) and nuclear migration

4. Basidiomycete mating, part 1 Precise branch positioning and determinate growth Septum modification and nuclear migration Nuclear proliferation and hyphal invasion

5. Clamp connections in basidiomycete dikaryons

6. B: hyphal growth A: pathogenesis A and B functions are distinct • in heterobasids (....?) • A controls pathogenicity • B controls filamentous growth karyogamy, meiosis, sporulation

7. Using genetics to explore biology:mutants in experimental fungal systems • spontaneous mutations or mutagenesis (uv, chemicals) • each gene is named for 1st described mutation • Example: gene for pigmentation is called “white” because the mutant lacked colouration

8. Gene naming systems • Genes – generally, three-letters plus a letter or number – cdc2, CDC28, nimX (species specific) • Alleles – generally a numeral, e.g.nimX3 • Allele descriptors – nimX3 Y305H • Other descriptors – “+” wildtype, D dominant, ts temperature sensitive, D deletion • Gene product – p34cdc2, NIMX • Gene name + product identifier – nimXcdc2

9. Mating and progeny analysis in Aspergillus nidulans

10. The genetics of spore colour in A. nidulans • The ability to make pigment is controlled by the gene called white • The first mutant had white spores, wA • Wildtype green is WA (typically wildtype alleles are not written in the genotype) • WA and wA are allelic

11. Colour can be modified • If a strain is WA, then it has pigmented spores • Colour can be modified by other genes • Green pigment formation takes two steps, only the first of which is controlled by white

12. Mating white and green strains • Cross WA::wA (two alleles of the same gene locus) • Pattern of colour inheritance? • WA::wA  WA : wA = 1:1

13. Two steps for making green pigment • The yellow gene is required for making green pigment • Wildtype allele is YA; mutant is yA • If a strain has yellow spores, which allele is at the w/W locus? • YA::yA  progeny genotype, phenotype, proportions?

14. Mating a white and a yellow strain • wA::yA • Implications regarding w/W? • Since the yellow strain is yellow, it must be WA yA • The white strain is wA but unknown for yAvsYA • Epistasis

15. How do we find out? • Mate wA strain to yA • If wA, YA :: WA, yA white :: yellow • wA, YA; WA, yA; wA, yA; WA, YA • white yellow white green • If wA, yA :: WA, yA white :: yellow • wA, yA; WA, yA; wA, yA; WA, yA white, yellow, white, yellow