Editing Evolutionary developmental biology (section)

===Gene toolkit===
{{Main|Evo-devo gene toolkit}}
{{Further|Plant evolutionary developmental biology}}

[[File:Hoxgenesoffruitfly.svg|thumb|upright=1.25|Expression of [[Hox gene|homeobox (Hox) genes]] in the fruit fly]]

A small fraction of the genes in an organism's genome control the organism's development. These genes are called the developmental-genetic toolkit. They are highly conserved among [[Phylum|phyla]], meaning that they are ancient and very similar in widely separated groups of animals. Differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. Most toolkit genes are parts of [[signalling pathway]]s: they encode [[transcription factor]]s, [[cell adhesion]] proteins, cell surface [[receptor (biochemistry)|receptor]] proteins and signalling [[Ligand (biochemistry)|ligands]] that bind to them, and secreted [[morphogens]] that diffuse through the embryo. All of these help to define the fate of undifferentiated cells in the embryo. Together, they generate the patterns in time and space which shape the embryo, and ultimately form the [[body plan]] of the organism. Among the most important toolkit genes are the [[Hox gene|''Hox'' genes]]. These transcription factors contain the [[homeobox]] protein-binding DNA motif, also found in other toolkit genes, and create the basic pattern of the body along its front-to-back axis.<ref name=Carroll_2008/>
Hox genes determine where repeating parts, such as the many [[vertebra]]e of [[snake]]s, will grow in a developing embryo or larva.<ref name=CarrollNatHist/> ''Pax-6'', already mentioned, is a classic toolkit gene.<ref>{{Cite journal |last=Xu, P.X. |last2=Woo, I. |last3=Her, H. |last4=Beier, D. R. |last5=Maas, R. L. |year=1997 |title=Mouse Eya homologues of the Drosophila eyes absent gene require Pax6 for expression in lens and nasal placode |journal=Development |volume=124 |issue=1 |pages=219–231 |doi=10.1242/dev.124.1.219 |pmid=9006082}}</ref> Although other toolkit genes are involved in establishing the plant [[bodyplan]],<ref>{{Cite journal |last=Quint |first=Marcel |last2=Drost |first2=Hajk-Georg |last3=Gabel |first3=Alexander |last4=Ullrich |first4=Kristian Karsten |last5=Bönn |first5=Markus |last6=Grosse |first6=Ivo |date=2012-10-04 |title=A transcriptomic hourglass in plant embryogenesis |journal=Nature |volume=490 |issue=7418 |pages=98–101 |bibcode=2012Natur.490...98Q |doi=10.1038/nature11394 |issn=0028-0836 |pmid=22951968 |s2cid=4404460}}</ref> [[homeobox]] genes are also found in plants, implying they are common to all [[eukaryote]]s.<ref name="pmid19734295">{{Cite journal |last=Mukherjee |first=K. |last2=Brocchieri, L. |last3=Bürglin, T.R. |date=December 2009 |title=A comprehensive classification and evolutionary analysis of plant homeobox genes |journal=Molecular Biology and Evolution |volume=26 |issue=12 |pages=2775–94 |doi=10.1093/molbev/msp201 |pmc=2775110 |pmid=19734295}}</ref><ref name="pmid9336443">{{Cite journal |last=Bürglin, T.R. |date=November 1997 |title=Analysis of TALE superclass homeobox genes (MEIS, PBC, KNOX, Iroquois, TGIF) reveals a novel domain conserved between plants and animals |journal=Nucleic Acids Research |volume=25 |issue=21 |pages=4173–80 |doi=10.1093/nar/25.21.4173 |pmc=147054 |pmid=9336443}}</ref><ref name="pmid17501745">{{Cite journal |last=Derelle |first=R. |last2=Lopez, P. |last3=Le Guyader, H. |last4=Manuel, M. |year=2007 |title=Homeodomain proteins belong to the ancestral molecular toolkit of eukaryotes |journal=Evolution & Development |volume=9 |issue=3 |pages=212–9 |doi=10.1111/j.1525-142X.2007.00153.x |pmid=17501745 |s2cid=9530210}}</ref>