Editing Comparative genomic hybridization (section)

===Isolation of DNA from test tissue and reference tissue===

Standard [[phenol extraction]] is used to obtain DNA from test or reference (karyotypically normal individual) tissue, which involves the combination of [[Tris]]-[[Ethylenediaminetetraacetic acid]] and [[phenol]] with [[aqueous solution|aqueous]]  DNA in equal amounts. This is followed by separation by agitation and centrifugation, after which the [[aqueous solution|aqueous]] layer is removed and further treated using [[diethyl ether|ether]] and finally [[ethanol precipitation]] is used to concentrate the DNA.<ref name="Weiss,Hermsen,Meijer,VanGrieken,Baak,Kuipers,VanDiest" />

May be completed using DNA isolation kits available commercially which are based on [[Affinity chromatography|affinity columns]].<ref name="Weiss,Hermsen,Meijer,VanGrieken,Baak,Kuipers,VanDiest" />

Preferentially, DNA should be extracted from fresh or frozen tissue as this will be of the highest quality, though it is now possible to use archival material which is formalin fixed or paraffin wax embedded, provided the appropriate procedures are followed. 0.5-1&nbsp;μg of DNA is sufficient for the CGH experiment, though if the desired amount is not obtained DOP-PCR may be applied to amplify the DNA, however it in this case it is important to apply DOP-PCR to both the test and reference DNA samples to improve reliability.<ref name="Weiss,Hermsen,Meijer,VanGrieken,Baak,Kuipers,VanDiest" />