Two factors, A/B (mostly basids)Tetrapolar mating system meiosis gives four types of segregantsNeed different alleles at each mating locus A1B1 :: A2B2 A1B1, A1B2, A2B1, A2B2Schizophyllum has ~28,000 mating type combinations

Basidiomycete matingMating dikaryon formation fruiting Mating uses pheromones + receptors that signal through a kinase cascade

for heterobasidiomycetesfruit body

A and B functions are distinctin 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

Basidiomycete mating, part 1Precise branch positioning and determinate growth

Septum modification and nuclear migration

Nuclear proliferation and hyphal invasion

Clamp connections in basidiomycete dikaryons

A and B functions are distinctin heterobasids (....?) A controls pathogenicity B controls filamentous growthkaryogamy, meiosis, sporulation

Using genetics to explore biology:mutants in experimental fungal systemsspontaneous mutations or mutagenesis (uv, chemicals)each gene is named for 1st described mutationExample: gene for pigmentation is called white because the mutant lacked colouration

Gene naming systemsGenes generally, three-letters plus a letter or number cdc2, CDC28, nimX (species specific)Alleles generally a numeral, e.g. nimX3 Allele descriptors nimX3 Y305HOther descriptors + wildtype, D dominant, ts temperature sensitive, D deletionGene product p34cdc2, NIMXGene name + product identifier nimXcdc2

Mating and progeny analysis in Aspergillus nidulans

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

Colour can be modifiedIf a strain is WA, then it has pigmented sporesColour can be modified by other genesGreen pigment formation takes two steps, only the first of which is controlled by white

Mating white and green strainsCross WA::wA (two alleles of the same gene locus)Pattern of colour inheritance? WA::wA WA : wA = 1:1

Two steps for making green pigmentThe yellow gene is required for making green pigmentWildtype allele is YA; mutant is yAIf a strain has yellow spores, which allele is at the w/W locus?YA::yA progeny genotype, phenotype, proportions?

Mating a white and a yellow strainwA::yAImplications regarding w/W?Since the yellow strain is yellow, it must be WA yAThe white strain is wA but unknown for yA vs YAEpistasis

How do we find out?Mate wA strain to yAIf wA, YA :: WA, yA white :: yellowwA, YA; WA, yA; wA, yA; WA, YAwhite yellow white greenIf wA, yA :: WA, yA white :: yellowwA, yA; WA, yA; wA, yA; WA, yAwhite, yellow, white, yellow