Karyotype analysis: The detection of chromosomal alterations in the somatic karyotype of Zea mays L.

Mitotic analyses, directed at the problem of detection of chromosomal alterations in the somatic karyotype, were performed using six reciprocal interchanges of Zea mays L., all involving chromosome 9S. In addition, two normal stocks, a homozygous inbred and a commercial hybrid were examined. The minimum chromosome alteration in 9S detected in somatic metaphase was a decrement measured as 50% of the pachytene chromosome; an increment to 9S measured as 40% of the pachytene chromosome was not detected. However, a 10% meiotic increment to 5L was observed. Ascertainment in mitotic metaphase of chromosomal alterations in maize, of the type that change chromosome length and/or centromere position, appears to be dependent upon centromere position (metacentric, aerocentric) in addition to the nature of the alteration (increment or decrement). Relatively short alterations may be detected in metacentric, but not in the submetacentric or acrocentric chromosomes. A decrement rather than an addition segment in a non-metacentric chromosome appears more readily detectable in somatic metaphase.