A Dihybrid Cross uses mutants with different phenotypes to demonstrate dominant and recessive gene expression. By making all possible crosses of these strains in both mating types, we get a graphic demonstration of the dominant and recessive relationships of the red color vs cream color, and adenine-dependence vs adenine independence. This cross also illustrates a development in genetics that was essential for understanding the nature of the gene at the molecular level. This is a genetic test for allelism. It demonstrates that the two mutations ade1 and ade2 are not allelic in spite of having the same phenotype.
Geneticists get tired of writing the same symbols repeatedly and use a simple shorthand.
The two different media, YED and MV, allow you to distinguish the mutant phenotype from the normal phenotype, but does not let you distinguish among the different mutant strains. Tape the mating grid to the bottom of a YED plate. Use the grid as a guide. Incubate the plate overnight. Using sterile toothpicks transfer and mix the haploid strains in all possible combinations at the intersections of the grid.