Maize, commonly known as corn, is a large grain plant domesticated by indigenous peoples in Mexico in prehistoric times about 10,000 years ago. The six major types of corn are dent corn, flint corn, pod corn, popcorn, flour corn, and sweet corn.
The leafy stalk of the plant produces separate pollen and ovuliferous inflorescences or ears, which are fruits, yielding kernels (often erroneously called seeds). Maize kernels are often used in cooking as a starch.
Many forms of maize are used for food, sometimes classified as various subspecies related to the amount of starch each has:
Flour corn: Zea mays var. amylacea
Popcorn: Zea mays var. everta
Dent corn : Zea mays var. indentata
Flint corn: Zea mays var. indurata
Sweet corn: Zea mays var. saccharata and Zea mays var. rugosa
Waxy corn: Zea mays var. ceratina
Amylomaize: Zea mays
Pod corn: Zea mays var. tunicata Larrañaga ex A. St. Hil.
Striped maize: Zea mays var. japonica
This system has been replaced (though not entirely displaced) over the last 60 years by multivariable classifications based on ever more data. Agronomic data were supplemented by botanical traits for a robust initial classification, then genetic, cytological, protein and DNA evidence was added. Now, the categories are forms (little used), races, racial complexes, and recently branches.
Maize is a diploid with 20 chromosomes (n=10). The combined length of the chromosomes is 1500 cM. Some of the maize chromosomes have what are known as “chromosomal knobs”: highly repetitive heterochromatic domains that stain darkly. Individual knobs are polymorphic among strains of both maize and teosinte.
Barbara McClintock used these knob markers to validate her transposon theory of “jumping genes”, for which she won the 1983 Nobel Prize in Physiology or Medicine. Maize is still an important model organism for genetics and developmental biology today.
The Maize Genetics Cooperation Stock Center, funded by the USDA Agricultural Research Service and located in the Department of Crop Sciences at the University of Illinois at Urbana-Champaign, is a stock center of maize mutants. The total collection has nearly 80,000 samples. The bulk of the collection consists of several hundred named genes, plus additional gene combinations and other heritable variants. There are about 1000 chromosomal aberrations (e.g., translocations and inversions) and stocks with abnormal chromosome numbers (e.g., tetraploids). Genetic data describing the maize mutant stocks as well as myriad other data about maize genetics can be accessed at MaizeGDB, the Maize Genetics and Genomics Database.