The B-A translocations of maize provide the most efficient method for locating the recessive genes (mei-genes especially) to the proper chromosome arm (Roman, Genetics 32:391, 1947; Roman, Ullstrup, Agr. J. 43:450, 1952; Beckett, J. Hered. 69:27, 1978). The cytogenetical data for mapping the mei-gene ms43, which induced abnormal chromosome segregation at the anaphase I of meiosis and male sterility, have been presented here.
For this aim the female plants homozygous for Ms43 were crossed by 18 stocks with B-A translocations kindly provided by G. B. Fletcher (Coop. Stock Center, USA). The F1 progenies from 15 cross combinations were studied cytologically. Thirty seeds from each cross combination were planted in a greenhouse. The pattern of meiosis and number of chromosomes at diakinesis-metaphase I have been analysed in each F1 plant.
Based upon cytological examination of F1 plants, the conclusion was made that ms43 gene is uncovered by TB-8La. Among the progeny from the ms43/ms43 x TB-8La cross, a total of 27 plants were examined. Twenty-two plants with normal meiosis composed the hyperploid class: 9 plants had 21 chromosomes and 13 had 22 chromosomes. Four plants were hypoploids, one of them appeared to be ms43 phenotype (Figure 1, Table 1).
The cytological data from cross combination with TB-10Sc were excluded from the total data, because all of the 14 F1 plants studied had 10 bivalents at diakinesis-metaphase I of meiosis. This could mean that the individual male plant used in the cross with the ms43 homozygote had no BA chromosomes.
A total of 238 F1 plants from the 13 remaining cross combinations were analysed. No mutant plant with ms43 spindle phenotype was found. Forty-four plants had 10 bivalents at diakinesis-metaphase I of meiosis and composed the hypoploid class. The hyperploid class contained 65 plants with 11 bivalents at diakinesis-metaphase 1, and 27 plants with 10 bivalents and 1 univalent.
Based upon cytological data the ms43 gene is placed on the long arm of chromosome 8.
The ms43 gene is the 15th gene which has been localized in chromosome 8 (Coe et al., 1983, MNL 57:175; Curtis, 1983, MNL 57:32). It is very interesting that the genes ms43, el and ms8 are placed on the same chromosome.
The preferential or "directed" fertilization of the eggs by hyperploid sperms is clear from the cytological data (Table, right part). However, the TB-A stocks used in the experiment differed significantly from one another for this characteristic. The directed fertilization is strongly marked in the TB-8La and TB-9S, and is obvious in the TB-3La, 3Sb, 10La. The TB-6Sa has an opposite tendency. The chance to fertilize the eggs with hypoploid and hyperploid sperms is nearly equal in the TB-9La.
Figure and Table.
I.N. Golubovskaya and E.E. Distanova
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