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
for heterobasidiomycetes
fruit body

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
hyphal invasion

5. Clamp connections in basidiomycete dikaryons

6. A and B functions are distinct
in heterobasids (....?)
A controls pathogenicity
B controls filamentous growth
A: pathogenesis
B: hyphal 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 yA vs YA
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