Frequency of appearance of Ura+His+ papillae in strains carrying a modified chromosome. Haploid strains were grown to log phase in raffinose-containing medium, exposed to galactose (dark bars) or not (light bars), then plated to glucose-containing medium lacking uracil and histidine. Papillae were scored after 3 days. Bars represent the mean frequencies ± standard deviations from at least 2 independent trials. (A) Strains carrying modified chromosome III were KAY418 and KAY419; modified IV, KAY614 and KAY619; modified VI, KAY539 and KAY568. (B) Strains carrying modified chromosome VI were KAY591 and KAY628 that harboured vectors pRS425 (2-micron) or pRS315 (CEN), or TUB1 plasmids pRB327 (2-micron) or pKA55 (CEN). The frequencies in strains treated with no galactose (light bars) are not statistically different from each other, with one exception. Strains with modified VI that carry pTUB1 plasmids exhibited higher spontaneous frequencies than did VI strains without pTUB1 (Tukey-Kramer test, p < 0.05).