Recently, Genomic or expression microarray technology become a common tool for genome and gene investigation in research and development and clinical diagnostic. For genome profiling and hight resolution molecular karyotyping, array comparative genome hybridisation ( array CGH) methods appear to be far better as they do not suffer from dependence on having metaphase preparations and have much higher sensitivity and specificity for subtle genomic changes Clinical applications of array CGH were made possible by developments in the human genome project and associated technologies. Such developments now allow for identification of sequences mapped to specific regions, arraying them on a slide, and using this array for comparing test and control DNA. This made high-resolution analysis feasible as a diagnostic tool for the comprehensive analysis of detailed chromosomal alterations of DNA copy numbers. Further, unlike classic CGH, array CGH is more amenable to automation and thus significant cost cutting. In prenatal diagnosis, the analysis of first trimester abortion by microarray suggest that classic cytogenetics of spontaneous abortion may yield normal karyotypes or selected abnormal karyotypes that permit cell proliferation in vitro while Array CGH detects other abnormalities. In Prenatal medicine, array CGH is becoming an important clinical assay for unbalanced chromosome abnormalities whether cells grow in culture or not and in cases of analysis on one or few cells. In postnatal diagnosis the one mega base molecular karyotyping, is giving a grate information for malformatives and microdeletions syndrome identification, also for genome investigation for infertile couple undergoing IVF for better comprehesion of chromosome disorders contribution in reproductive pathology. For the next few years, array based CGH will become routinely used in clinical and molecular genetics in areas ranging from preimplantation genetic diagnosis to fetal losses to cancer and beyond for chromosome or mutation analysis.