A haploid strain of Aspergillus nidulans carried an auxotrophic met-8 mutation conferring a requirement for methionine. Several million asexual spores were plated on minimal medium, and two prototrophic colonies grew and were isolated. These prototrophs were crossed sexually with two different strains, with the progeny shown in the body of the following table, where met+ means that methionine is not required for growth and met- means that methionine is required for growth.
crossed with Prototroph
a) Explain the origin of both of the original prototrophic colonies.
b) Explain the results of all four crosses, using clearly defined gene symbols.