MAIZE

Maize ( /ˈmeɪz/ mayz; Zea mays L, from Spanish: maíz after Taíno mahiz), known in many English-speaking countries as corn, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable or starch. The Olmec and Mayans cultivated it in numerous varieties throughout Mesoamerica, cooked, ground or processed through nixtamalization. Beginning about 2500 BCE, the crop spread through much of the Americas.The region developed a trade network based on surplus and varieties of maize crops. After European contact with the Americas in the late 15th and early 16th centuries, explorers and traders carried maize back to Europe and introduced it to other countries. Maize spread to the rest of the world due to its ability to grow in diverse climates. Sugar-rich varieties called sweet corn are usually grown for human consumption, while field corn varieties are used for animal feed and as chemical feedstocks.
Maize is the most widely grown grain crop in the Americas, with 332 million metric tons grown annually in the United States alone. Approximately 40% of the crop — 130 million tons — is used for corn ethanol. Transgenic maize (genetically modified corn) made up 85% of the maize planted in the United States in 2009.While some natural strains of maize can grow 12 metres (39 ft) tall, most commercially grown maize has been bred for a standardized height of 2.5 metres (8.2 ft). Sweet corn is usually shorter than field corn varieties.
Genetics
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 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 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.