Low Deficiency Rate in Embryo vs. Endosperm with UV. In both UV progenies the frequency of plants with segregating defective pollen was about 20 per cent. There is reason to believe that many of these are due to causes other than deficiency (notably to mutations producing subnormal pollen). But even if all were due to deficiency, their frequency is far lower than would be anticipated from the endosperm deficiency rates. The seeds planted showed endosperm deficiencies amounting to about 36 per cent for the marker genes A, Pr, and Su; these could represent only a small fraction of the deficiencies present in the entire ten chromosomes of the treated gamete. With equal deficiency frequency in the embryo, almost all of the F1 plants should have segregating defective pollen due to deficiency, and many should have several deficiencies.

At one marked locus, a direct comparison may be made. The seeds planted in the two UV progenies included 71 endosperm deficiencies for A; the F1 plants included no A deficiencies.

Although induced deficiencies are relatively rare in the F1 embryos, it is certain that they are not wholly absent. The treated pollen carried the dominant markers A B Pl Rr; the UV families included five genetically marked deficiencies and several unmarked deficiencies which were identified cytologically in defective plants. Only one deficiency (a monosomic for chromosome #6) was found in the much larger control population.