Marker-assisted breeding using genetic markers
Domestication of crops began over 10,000 years ago but the domestication and breeding of trees is much more recent, beginning less than 100 years ago. Breeding of trees in recent years has been helped by the use of genetic DNA sequence variants that act as indirect markers of the trait being selected. This is known as marker assisted breeding. At first the type of variant was a restriction fragment length polymorphism (RFLP) – a sequence variant that could be detected by the ability (or inability) of a sequence-specific DNA-cutting enzyme (called a restriction enzyme). More recently, single nucleotide polymorphisms (SNPs) have been used for this purpose.
For a more detailed source of reference, please see the informative review published by Neale and Kremer (2011) in Nature Reviews Genetics.
Great British Trees - identification and genetics 