gene Flow: Implications for Crop Diversity and Wild Relatives

Chapter 2Overview of Vertical Gene Transfer(Gene Flow)2.1 What is gene flow?Gene flow is the movement of genes from one population toanother, conferring new traits – the biophysical characteristics ofthe organism – to individuals of the recipient population. Thishappens by cross-pollination (also called hybridisation), that is, thepollination of members of one population or genetic pool withthat of another. The outcrossing of genes is said to be ‘vertical’as the genetic information is passed ‘down’ from parents tooffspring. This is contrasted with horizontal gene transfer, wherethe acquisition of genes is passed over, i.e. ‘horizontally’, fromone organism to another by means other than inheritance.Vertical gene flow often results in introgression, the establishmentof alleles (gene variants), or wholly new genes (as is the casewith transgenes) in the recipient population.Therefore, vertical gene flow is restricted to organisms that canmate with one another and make offspring. In the case of cropplants, which are domesticated forms of wild plants, a highdegree of compatibility can therefore exist between the cropand wild and weedy relatives. Gene flow can be from crop tocrop (or landrace), from crop to wild relative, and even fromwild relative to crop plant. Gene flow has been a natural, andin some cases desirable, part of evolution and speciation inflowering plants (Anderson 1961; Reiseberg & Wendel 1993;3