It used to be the case but there are powerful groups having good success in changing it (and making great profits as a result). See http://www.forbes.com/sites/alexmorrell/2014/03/26/can-this-... for one story.

Controlling the germplasm for staple crops like soybeans and corn is hugely profitable. As a percentage of crop inputs, the cost of quality seed has been rising at a crazy rate. Allowing patents of genes is one way of directing money to plant breeding. However, I think long term it is a bad policy, much like allowing extremely long copyright terms on creative works. Society will suffer when the available public domain material shrinks.