TABLE 3.

Spontaneous appearance of [URE3] in S. cerevisiae, S. paradoxus, and S. uvarum

Species	[Ade+] per 107 cells	[URE3] frequency
S. cerevisiae	710	6.8 × 10−6
S. paradoxus	220	<10−7
S. uvarum	830	4.2 × 10−5

After overnight growth in YPD rich medium, 10⁷ cells were plated onto SD medium without adenine. After 8 days of growth, the number of [Ade⁺] were counted. The [URE3] status of 200 [Ade⁺] clones was then monitored as described in the results (cure, dominance, segregation) except for S. paradoxus where all the [Ade⁺] clones were analyzed. All the [Ade⁺] clones that were cured by guanidine hydrochloride displayed a non-Mendelian segregation.