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Veracity of tetrads was monitored through segregation of the
nuclear markers his and lys . All tetrads reported showed 2:2
segregation of these markers.
An unequivocally Mendelian pattern of segregation for GR was
shown by 4B2/133 (Table III) . Resistant segregants showed homogeneous
colony resistance which could be scored 24 hr after replica plating
on GGM. In contrast, all the other strains required the usual 3 days
on GGM before adequate growth was attained for scoring. Resistance in
segregants of these strains was of the microcolony type and did not
show Mendelian segregational patterns (Table III)
Stability of Cytoplasmic G
A decline of resistance over storage periods was suspected when
older cultures consistently showed low resistance. Cultures of GR6
and GR7 (YPD slopes) which had been utilized for vegetative segregational
analysis were retested after 4 months storage at 4°. The percentage
of vegetative segregants capable of producing some level of resistance
had been markedly reduced (Fig. 6)
Vegetative Segregation in a_ 4:0, r :s Ascus
Single spore isolates from a 4:0, resistant: sensitive ascus of
8/4BL were tested for vegetative segregation of resistance. The spore
lines designated 8J1, 8J2, 8J3 and 8J4 showed high levels of microcolony
resistance (Fig. 7) . Only 8J4 yielded sensitive isolates.