RECOVERY FOLLOWING GENETIC DEFICIENCY IN MAIZE

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Abstract
Deficiency is the loss or inactiva-tion of a section, or the whole, of a chromosome. Recovery is defined as the return to normal activity of genes previously deficient. Tassels of plants homozygous dominant for A R C Wx and Pr were treated to x-rays and the pollen used on plants of the genetic composition a R C pr. Among 3916 seeds produced 27 were colorless, indicating loss of A, and 9 were red, indicating loss of Pr. In addition, 18 seeds were colorless except for one or more small, colored spots, and 4 were red except for similar spots of, purple. The average area showing the dominant character was less than 1/100 of the endosperm surface. The same treated pollen used on plants of A R c wx produced 2374 seeds of which 27 were colorless (18 white waxy and 9 white horny). In addition there were 5 white waxy seeds with small spots of colored horny tissue. The fact that the recovery in every instance affected both characters simultaneously is held to preclude reverse mutations as an explanation. Reasons are given against explaining the occurrence of the small spots as extreme examples of chimera. Recovery was observed also in untreated material. In 700 examples of endosperm chimeras, there were several cases in which small spots occurred in the deficient sector and 11 seeds with the entire endosperm deficient except for one or more small spots. The frequency of deficient endosperm showing recovery was as high in the untreated as in the treated seed. One example of recovery in the sporophyte is reported,[long dash]a green plant deficient for A that developed narrow red stripes on the lower leaf sheaths. A suggested mechanism providing for recovery is that deficiency deprives the chromosome of its power to reproduce itself without destroying its other functions. If later the ability to divide is restored, the cell descendants would constitute an island of tissue showing the dominant character.

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