Comparative  genomic    hybridization   (CGH)   is  a molecular  cytogenetic  method  for  analysing copy number variations (CNVs) relative to ploidy  level  in the DNA of a test sample compared to  a   reference sample, without the need for   culturing   cells.   The aim of this technique is to   quickly   and   efficiently compare  two  genomic  DNA  samples  arising from two sources, which are most  often  closely  related, because     it   is    suspected      that    they   contain differences in terms of either  gains   or   losses    of either  whole   chromosomes   or   subchromosomal regions     (a portion of a whole chromosome).   This technique   was   originally      developed    for     the evaluation    of     the    differences     between    the chromosomal complements of    solid   tumor     and normal tissue,[1] and has an improved resolution  of 5–10 megabases compared to the more    traditional cytogenetic analysis techniques of  giemsa banding and fluorescence in situ hybridization  (FISH)  which are limited by the resolution    of    the    microscope utilized.