The Role of Genes in Modern Bread Wheat

The growth characteristics of wheat are controlled by the genes within the cells of the plants. These are linked into long chains, the chromosomes, that together form the cell genome. Wheat has a large genome of 42 chromosomes, created during the evolution from the three wild species.

Wheat was originally a very tall plant, as seen in "The Corn Harvest" painted by Pieter Bruegel the Elder in 1565. This shows wheat growing up to the heads of the men harvesting it with scythes.
After the discovery of shorter landraces in Japan, wheat breeders transferred selected Reduced-height (Rht) genes from different landraces to create the shorter but higher yielding wheat varieties more suited to modern farming. Most modern combines are unable to harvest tall cereals with long straw due to blockage problems.
The picture shows the wheat variety "Mercia" with a control and four lines with different Rht genes.
Rht-0, with no reduced-height gene, is used as the control for height comparison.
Rht-1 and Rht-2 typically produce semi-dwarf plants, two-thirds the height of the control.
Rht-3 and Rht-12 typically produce dwarf plants, one-third the height of the control.

Plants with the Rht-12 gene also have awns on the ears, the awn and Rht genes occurring close together on the same chromosome. Almost all modern varieties of wheat now include height reducing genes, often Rht-1 or Rht-2, occasionally Rht-3 or other Rht genes to control the final height of the plants.

The information displayed on the role of genes display board is available as a 'pdf' file.