Table 3

Segregation of tester chromosomes. Data are the percentage of tetrads per class and, in parentheses, the actual number scored. The assays for segregation errors were performed as described with yeast strains containing homologous and heterologous linear human YACs (pairs A and F) (8). Each YAC contains a specific centromere marker whose segregation can be monitored relative to the segregation of a centromere marker on chromosome VI. Circular centromere plasmids were pMCB248, a randomly cloned 8.1-kb Bam HI fragment from chromosome XIII in pRS314, and pMCB249, a random 6.8-kb Bam HI fragment from chromosome XIV in pRS316. Their segregation was assayed in the same strain background as for the linear YACs. The classes of segregation errors are (i) nondisjunction, both YACs or plasmids go to the same pole at the first division; (ii) PSS (precocious sister separation), sister chromatids of one YAC or plasmid segregate to opposite poles at meiosis I; (iii) PSS×2 (double precocious sister separation), sister chromatids from both YACs or plasmids separate prematurely; and (iv) abnormal meiosis II, chromosome loss or nondisjunction at the second division results in one pair of sister spores with normal segregation and the other pair with one member missing a YAC or plasmid. Significant effects (Gtest) of ndj1Δ were detected for the disjunction of heterologs [G = 9.97; 1 degree of freedom (df);P < 0.005], combined PSS and PSS×2 of homologs (G = 4.53; 1 df; P < 0.05), and meiosis II errors of homologs (G = 3.75; 1 df; P = 0.05).

Meiosis I* Disjunction100  (45)99  (106)89  (34)62  (43)80  (28)86  (55)
Nondisjunction0  (0)1  (1)11  (4)38  (26)20  (7)14  (9)
Meiosis INon-PSS100  (45)95  (107)83  (38)73  (69)75  (35)80  (64)
PSS0  (0)4  (5)15  (7)17  (16)23  (11)19  (15)
PSS×20  (0)1  (1)2  (1)10  (9)2  (1)1  (1)
Meiosis IINormal98  (44)89  (101)91  (42)89  (84)89  (42)85  (68)
Abnormal2  (1)11  (12)9  (4)11  (10)11  (5)15  (12)
Total tetrads4511346944780
  • * Excludes tetrads with PSS or PSS×2.