A chromosomal disjoining and rejoining technique was developed to permit a balanced lethal system (Figure 1). Using this technique, line 394, which is regulated by a balanced lethal system (Salerno, MNL 58:52), was crossed with a normal line (without lethals). This resulted in disjoining of the lethal chromosome pair. Then, the F1 plants were self-pollinated. The F2 generation grown in the greenhouse segregated two 3:1 heterozygotes to one normal, to one lethal.

The two heterozygous progenies of the F2 generation were planted in the field. At maturity, they were intercrossed. The progenies of this intercrossing, grown in the greenhouse, segregated 1:1 lethal to normal, in a balanced lethal system again. These progenies also segregated two 3:1 heterozygotes to one normal.

Figure 2 shows what happens when a cross is made between two balanced lethal systems. This technique would permit increasing the variability of these lines through the use of such a balanced lethal system.

Figure 1. Disjoining and rejoining of a balanced lethal system.

Figure 2: Cross between balanced lethal systems.

Juan C. Salerno

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