Diploid strains of asci, placed on suitable medium, sporulate and form four haploid spores/ascus, which may be arranged as tetrahedra, diamonds, or linearly. Strains forming linear arrays of spores in the ascus are rare, dissection of the asci with the micromanipulator is difficult, so the method is now little used. Hawthorne (1) used it extensively in his early studies of yeast genetics. Generally, the yeast spores are considered unordered, and the ascus walls are dissolved enzymatically and the spores separated with a micromanipulator and grown to form colonies, which may consist of haploid or diploid cells, depending on whether or not the strain is heterothallic. The segregation of auxotrophic or other markers can then be determined, and map distances, in centimorgans, estimated. Allelic relationships can also be investigated.