Basic Genome Structure

Genetic Maps:

Many genetic maps of maize have been created. Though initially housed at MaizeDB, a comprehensive source of information on the genetics and molecular biology of maize found at the University of Missouri at Columbia, complete datasets from MaizeDB can now be accessed at MaizeGDB, home of the Maize Genetics and Genomics Database project.

Chromosomes:

Maize has 10 chromosomes (n=10, 2n=20). The total genetic length of these chromosomes is roughly 1500cM. Many maize chromosomes have chromosomal knobs, or highly repetitive heterchromatic regions which stain darkly on chromosome spreads (see figure below). Individual knobs are polymorphic among races of maize and the various teosinte. In fact, they make excellent cytogenetic markers, and as such were critical to Barbara McClintock's proof of chromosomal inheritance in maize.

Along with the standard complement of chromosomes, maize can also have several unusual chromosomes. There is a version of chromosome 10 known as Abnormal 10 (Ab10) that causes meiotic drive. Meiotic drive is a distortion of normal Mendelian segregation so that the Ab10 chromosome is preferentially passed on. This chromosome interacts with knobs, and thus the prevalence of knobs is likely the result of meiotic drive. Additional chromosomes known as B chromosomes also exist in maize. These are small chromosomes with few if any genes, but B chromosomes have a selfish mechanism that distorts sperm production and fertilization.

The figure below illustrates the 10 maize chromosomes, as well as Abnormal 10. A green square indicates the position of the centromere, while the red circles indicate the positions of chromosomal knobs. The size of each circle indicates the relative size and frequency of that knob position in Zea mays ssp. parviglumis and mexicana.

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