"This is why rice is still somewhat shattering, unlike maize," Olsen says. "If you have complete loss of shattering it makes threshing very difficult; so it's a compromise."
A second trait in the domestication syndrome is loss of seed dormancy. A wild plant all of whose seeds sprouted at the first shower or warm spell would risk disaster, so most wild species hedge their bets and stagger the germination of seeds. But in the more controlled agricultural environment, where the seeds are sown all at once and reaped all at once, there is strong selection against seeds with this trait.
However, in this case too, it is possible to overshoot the mark. "In rice, if you completely select against dormancy you can get a phenomenon called pre-harvest sprouting, where grains germinate while they're still on the stalk," Olsen says. "That's another case where selection has gone too far, and you're losing crop productivity."
More than one way to make a domestic plant
Any plant breeder can tell the difference between a weed and a crop plant, but figuring out the genetic differences between them is much harder. Searching for the relevant changes among all the genetic variation in a species is like groping in a fog, because most of the variation is neutral and not linked to significant variation in the plant's phenotype.
Quantitative Trait Locus (QTL) mapping is a statistical method that looks for strong associations between particular phenotypic traits and short DNA sequences that identify, or mark, particular locations in the genome. It is particularly useful for studying the inheritance of complex traits that are influenced by many genes and their interactions with the environment.
The main goal of QTL mapping is to understand whether a trait is controlled by a few genes of large effect or many genes of small effect. The assumption is that ph
|Contact: Diana Lutz|
Washington University in St. Louis