Three Cases of Deficiency in Chromosome 9 of Zea mays

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Abstract
Plants homozygous for the recessive allelomorphs of the genes yg 2, c, sh and v[image], and possessing a small knob on the end of a normal chromosome 9, were pollinated with X-rayed pollen from a plant homozygous for the dominant allelomorphs of the above genes, possessing a large terminal knob on a modified chromosome 9. Three exceptional F1 plants which were yellow-green, indicating a loss or an inactivation of the dominant Yg 2, were examined cytologically. One showed that a truly terminal portion of a chromosome can be deleted. The 2nd case was that of an internal deletion near the end of the chromosome. A comparison of the configurations observed in these 2 deletions demonstrated the necessity for care in distinguishing a terminal deletion from one occurring near the end of a chromosome, particularly in cases where the end of the chromosome is not visibly marked. The 3rd deletion included only a very small part of the chromosome. The [male] and [female] gametes possessing the deficiency were fully viable and functional in competition with normal gametes. Zygotes heterozygous for the deficiency gave plants indistinguishable from normal homozygous recessive plants in appearance and vigor Whether zygotes homozygous for the deficiency are viable has not been determined. From the 3 cases of deletion it is concluded that the gene yg 2 is located very-near the end of the short arm of chromosome 9.

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