Pachytene Chromosome Knobs of the Genus Zea: a Lifelong Research Project.

The story about my participation on the chromosome research on the genus Zea (maize and teosinte) began when I was hired in a new and unique project, coordinated by Dr. Barbara McClintock, for working out races from the whole American Continent, in the winter of 1959-1960.  The aim of this project was to get chromosome knob data from as many as possible plants of different maize and teosinte populations for gaining knowledge about the origin of maize and its genetic diversity. The methodology used was the concept of racial and geographic distribution patterns of chromosome knobs based on McClintock's experience on her studies of the controlling elements in maize, now known as transposons. The methodology became very effective: 1) maize was originated and domesticated from Mexican annual teosintes in Mesoamerica and it occurred multicentrically; 2) migrations and interactions among these original germplasms developed further special areas of new racial diversification indicating maize in Mexico has been genetically diverse since the time of its domestication; 3) analysis of the knob patterns also gave evidence about how and from where in Mesoamerica maize migrated to and/or introduced into other regions of the American Continent. This point of the project was reached in about 22 years. Among the data so far obtained there were some suggesting that maize and teosinte are genetically isolated; so, a further study was carried out comparing knob constitutions of Zea diploperennis and maize populations surrounding this teosinte; the results strongly support the preliminary conclusions. This has taxonomic implications and possibly there is a need to make some changes in the Zea classification. Chromosome knob analysis seems to be also efficient for elucidating individual race origin and its variability. At present, I am trying this with three races: Chalqueño, Cónico and Cónico Norteño. The work is still in process.