/ /2N-1 CHROMOSOMAL CHIMERA IN MAIZE BarBparaA McCiintock Botany Department, Cornell University HILE investigating the chromo- \ \ / some numbers in an Fy genera- tion of a cross of triploid maize (Zea mays) by diploid maize, an individual appeared whose micro- sporocytes showed a 2n-—1 chromo- some complement. The diploid chro- mosome number in maize is 20. Sporo- cytes of such plants normally show 10 bivalents at metaphase of the first meiotic division. ‘The presence of sporocytes showing only nine bivalents and one univalent (see Figure 20) in the first aceto-car- mine smears led to a ‘further investi- gation of the chromosome comple- ment in other parts of the tassel. The plant was very small and the tas- sel poorly developed, but approximately 150 clear figures were obtained from several different regions of the tassel. In all cases the sporocytes showed clearly 19 chromosomes, usually in the form of nine bivalents and one uni- valent. In anaphase the components of the nine bivalents disjoined and passed regularly to the two poles. The uni- valent usually lagged at the equator after the bivalents had disjoined, or lagged and split, the halves very fre- quently being eliminated from the re- organizing telophase nuclei. Several root tips were examined and all clear figures showed 20 chromo- somes. Such evidence points to the fact that early in the ontogeny of the upper part of this plant a chromosome must have been lost. Such occurrences are prob- ably not rare, but their detection is, since there are so few. cases men- tioned in the literature*. Unfortu- nately, for some undetermined reason, the plant gradually died before matur- ing pollen. *BrakesLee. A. F., and ‘BetuinG, J. Science, 55:19-20. LACKING A CHROMOSOME Figure 29 Photomicrograph from an eight months’ old permanently mcunted aceto - carmine smear showing a late metaphase figure with nine bivalents and one univalent. Made with the aid of a Leitz “Makam” camera, a periplanatic ocular, 18 mm. N, A. 1.25 Spencer achromatic objective, and a Wratten green filter No. 56. Magnification approxi- mately 650%. Chromoscmal chimeras in the Jimson weed. 218