M A I Z E - ZEA MAYS

Many forms of maize are used for food, sometimes classified as various subspecies:

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 multi-variable classifications based on ever more data. Agronomic data was 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 has 10 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 prove 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.

There is a stock center of maize mutants, 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. 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.

In 2005, the U.S. National Science Foundation (NSF), Department of Agriculture (USDA) and the Department of Energy (DOE) formed a consortium to sequence the maize genome. The resulting DNA sequence data will be deposited immediately into GenBank, a public repository for genome-sequence data. Sequencing the corn genome has been considered difficult because of its large size and complex genetic arrangements. The genome has 50,000–60,000 genes scattered among the 2.5 billion bases — molecules that form DNA — that make up its 10 chromosomes. (By comparison, the human genome contains about 2.9 billion bases and 26,000 genes.)

On February 26, 2008, researchers announced that they had sequenced the entire genome of maize.