Editing Gene pool (section)

== Gene pool concept in crop breeding ==
Harlan and de Wet (1971) proposed classifying each crop and its related species by gene pools rather than by formal taxonomy.<ref name= "Harlan&DeWet1971">{{cite journal|author1=Harlan, J.R. |author2=Wet, J.M.J.d. |year=1971|title=Toward a Rational Classification of Cultivated Plants|journal=Taxon|volume=20|issue=4|pages=509–517|jstor=1218252|doi=10.2307/1218252}}</ref>
#Primary gene pool (GP-1): Members of this gene pool are probably in the same "[[species]]" (in conventional biological usage) and can intermate freely. Harlan and de Wet wrote, "Among forms of this gene pool, crossing is easy; [[Hybrid (biology)|hybrids]] are generally fertile with good chromosome pairing; gene segregation is approximately normal and [[Horizontal gene transfer|gene transfer]] is generally easy.".<ref name= "Harlan&DeWet1971" /> They also advised subdividing each crop gene pool in two:
#*Subspecies A: Cultivated races
#*Subspecies B: Spontaneous races (wild or weedy)
#Secondary gene pool (GP-2): Members of this pool are probably normally classified as different species than the crop species under consideration (the primary gene pool). However, these species are closely related and can cross and produce at least some fertile hybrids. As would be expected by members of different species, there are some reproductive barriers between members of the primary and secondary gene pools:
#*hybrids may be weak
#*hybrids may be partially sterile
#*[[chromosomes]] may pair poorly or not at all
#*recovery of desired [[phenotype]]s may be difficult in subsequent generations
#*However, "The gene pool is available to be utilized, however, if the plant breeder or geneticist is willing to put out the effort required."<ref name= "Harlan&DeWet1971" />
#Tertiary gene pool (GP-3): Members of this gene pool are more distantly related to the members of the primary gene pool. The primary and tertiary gene pools can be intermated, but [[gene]] transfer between them is impossible without the use of "rather extreme or radical measures" <ref name= "Harlan&DeWet1971" /> such as:
#*embryo rescue (or embryo culture, a form of plant [[organ culture]])
#*induced [[polyploidy]] (chromosome doubling)
#*bridging crosses (e.g., with members of the secondary gene pool).