Dear community,

I did a tetrad dissection of yeast where I (hopefully) mated two markers into one stain. To be sure I selected real tetrads and to determine their mating type I did another mating with defined a and alpha strains that complement the URA3 deficiency of my new strains while the complements HIS and LYS deficiencies of the a and alpha test strains.

The results are shown in the picture below. None of the parental strains (marked blue) has grown on the selection medium and clone 1 has well grown after mating with a, so it should be alpha. However all mated areas have 2 to 4 colonies growing and clone 2 has grown quite well after mating with a and alpha.

My first theory was that all but clone 1 really are diploids which can't mate and grow but which can probably spontaneously sporulate on the selection medium and then mate and grow. This would explain the very few colonies for both mating types. This theory however can not explain that there are also a few colonies for clone 1 x alpha if it is haploid.

Did anyone have similar results or has an idea how to explain this?

Thank you for your help!

Best regards,

Felix