Editing Directional selection (section)

===African cichlids===
[[File:Labeotropheus fuelleborni in Botanic garden in Teplice (2).JPG|thumb|''Labeotropheus fuelleborni'']]
[[File:Metriaclima zebra.jpg|thumb|''Metriaclima zebra'']]
[[Cichlid|African cichlids]] are known to be a diverse fish species, with evidence indicating that they evolved extremely quickly. These fish evolved within the same habitat, but have a variety of [[Morphology (biology)|morphologies]], especially pertaining to the mouth and jaw. Experiments pertaining the cichlid jaw phenotypes was done by Albertson and others in 2003 by crossing two species of African cichlids with very different mouth morphologies. The cross between ''[[Blue mbuna|Labeotropheus fuelleborni]]'' (subterminal mouth for biting algae off rocks) and ''[[Zebra mbuna|Metriaclima zebra]]'' (terminal mouth for suction feeding) allowed for mapping of QTLs affecting feeding morphology. Using the QTL sign test, definitive evidence was used to support the existence of directional selection in the oral jaw apparatus in African cichlids. However, this was not the case for the suspensorium or skull QTLs, suggesting genetic drift or stabilizing selection as mechanisms for the speciation.<ref>{{cite journal | last1=Albertson | first1=R. C. | last2=Streelman | first2=J. T. | last3=Kocher | first3=T. D. | title=Directional selection has shaped the oral jaws of Lake Malawi cichlid fishes | journal=Proceedings of the National Academy of Sciences | volume=100 | issue=9 | date=2003-04-18 | issn=0027-8424 | doi=10.1073/pnas.0930235100 | pages=5252–5257| pmid=12704237 | pmc=154331| bibcode=2003PNAS..100.5252A | doi-access=free }}</ref>