Genes involved in domestication

Scientists are interested in learning more about the specific genes that control traits that have been involved in domestication. Understanding these genes can tell us a lot about the history of early humans and how agriculture started as well as about selection, gene function and genetic diversity. “Knowledge of past successes should help to intelligently guide future crop improvement” said John Doebley, a leading scientist in this field (Doebley 2006 Science). These traits are usually quantitative (controlled by more than one gene), so they can be complicated to study.

An example of a domestication gene that has been quite thoroughly studied is teosinte glume architecture or tga1 (gene names are by convention italicized). Teosinte seed are covered in a hard protective casing, which consists of the glume & cupule.  Because of the tga1 mutation, in maize this casing has receded to form the cob, exposing the naked kernel.  So maize kernels are much easier to eat or to prepare for cooking. Teosinte seeds look and feel like little stones.  This was the most critical step in the domestication of maize, as maize became a more edible food, and it is caused by a small change in just one gene. The function of this gene has yet to be determined but it may regulate organ identity. According to the authors of this research, “Our results demonstrate that modest genetic changes in single genes can induce dramatic changes in phenotype during domestication and evolution.”

It is also interesting to wonder how our ancestors discovered that teosinte was edible at all – perhaps they ate it when it was young and tender, or ground it into flour? – and knew that they had to save (not eat) some seeds for planting the next season.

Definition:
Quantitative trait – a trait or characteristic that cannot be accounted for by only one gene but rather is governed by several or many genes working together. These are called Quantitative Trait Loci, or QTL. 


Resources:

Doebley J (2006) Unfallen grains: how ancient farmers turned weeds into crops. Science 312: 1318 – 1319
John F. Doebley, Brandon S. Gaut, and Bruce D. Smith (2006) The Molecular Genetics of Crop Domestication. Cell 127: 1309 – 1321
Wang H, Nussbaum-Wagler T, Li B, Zhao Q, Vigouroux Y, Faller M, Bomblies D, Lukens L, Doebley JF (2005) The origin of the naked grains of maize. Nature 436: 713-719. doi:10.1038/nature03863