IntroductionIn the early years of scientific research in the field of heredity, the methods used to obtain data were considered genetic but once the physical basis of genetic conditions was recognised, different studies were performed using both cytological and genetic methods, using data collected through genetic procedures together with observations made using cytological techniques. This dual approach to the problems of heredity has been coined the term cytogenetics. Cytogenetics has provided insight into the genetic basis of disease as well as a powerful tool for diagnosing genetic conditions. Some of the traditional cytogenetic techniques are chromosome banding and fluorescence in situ hybridization (FISH). In chromosome banding the chromosomes are treated with different chemicals to color them and the coloring methods of the chromosomes are interpreted, based on the dyes used it could be G banding, Q banding, C banding or R banding. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original assayIn FISH, a nucleic acid probe is conjugated with a fluorescent dye, this is then used to detect complementary sequences on metaphase chromosomes or in interphase nuclei. After hybridization, the position of the bound probes is detected and analyzed using fluorescence microscopy and digital imaging technology. The traditional techniques mentioned above are powerful tools and on which the foundations have been laid, but they have their limitations, for example, chromosome banding is not able to detect deletions smaller than 5mb, i.e. microdeletions and in FISH it is necessary to select the probes appropriate to identify chromosomal aberrations. To overcome the shortcomings there have been several advances in the field, and these technological advances have helped improve our ability to investigate and define cellular processes at the molecular level, benefiting both scientists and clinicians. Some of the new FISH-based technologies are inverse FISH, multiplex FISH (M-FISH), spectral karyotyping (SKY), comparative genomic hybridization analysis (CGH), and array or microarray – CGH (M-CGH ). Instead of discussing all modern cytogenetic methods and their impact on disease basis identification and clinical diagnostic services, in this essay the focus will be on comparative genomic hybridization and its implications. Cytogenetic technologies have had an important impact in the field of medicine and in particular reproductive medicine and oncology, they have allowed us to understand and analyze the frequencies with which chromosomal aberrations occur during gametogenesis, embryonic development and developmental of the tumor. We are now able to better understand and detect genetic abnormalities associated with tumor origin, tumor progression, miscarriages, and congenital anomalies. CGH technology allows us to identify and map genomic regions for any chromosomal loss or gain in a single experiment without even having any knowledge of the chromosomal abnormality in question. CGH can produce a map of DNA sequence copy number changes as a function of chromosomal position across the entire genome. There are two ways to perform CGH, using the direct method or the indirect method, for the direct method we use fluorochromes while for the indirect method we use haptens, the use of haptens might be more advantageous in some cases as they are both convenient and more flexible. In case a standard ofreference for data analysis, CGH is performed with differently labeled normal DNA. To perform more detailed analysis, CGH is coupled with a sensitive monochrome cooled charge-coupled device (CCD) camera and automated image analysis software. The regions of DNA gain or loss will be represented as ratios between the intensity of the two fluorochromes on the chromosome being studied; in the case of chromosomal duplication or gene amplification in tumor DNA there would be increased green-red ratios while in chromosomal deletions there would be it would be a diminished ratio. Microarray-based comparative genomic hybridization (array CGH) is able to combine the advantages of molecular diagnostics together with traditional cytogenetic techniques and advancement in the field of cytogenetics. Studies conducted on individuals with developmental delay and dysmorphic features have demonstrated that array CGH has the ability to cause chromosomal aberrations such as duplications, deletions, amplifications, and aneuploidies. In case of individuals with normal results before cytogenetic testing, the detection rate of chromosomal aberrations was 5-17%, copy number variants (CNVs) can also be identified. Array CGH is a powerful tool with the potential to be a diagnostic tool for identifying visible, submicroscopic chromosomal abnormalities in mental retardation and other developmental disabilities. Tumor Genetics Cancer can aptly be described as a disease resulting from genomic instability, and given that CGH is designed to identify segmental genomic alterations, it is an appropriate tool for studying the genetic basis of cancer and its associated chromosomal abnormalities. Advances in array CGH technologies have made it possible to examine chromosomal regions in extraordinary detail and have revolutionized our understanding of the tumor genome. Several array-based technologies that are being developed to further improve CGH resolution will enable research to identify and analyze genomic regions responsible for cancer proliferation and facilitate rapid gene discovery. Take this case for example, the tumor suppressor gene p53 has been explored as a target for gene therapy in ovarian cancer, the idea is HER2/neu/erB2 for antibody-mediated therapy (Herceptin) and gene-mediated therapy by E1 A. In the study conducted by Kudoh et al. , were able to demonstrate that increased copy number presence in 1q21 and 13q13 correlated with lack of response to the chemotherapy regimen of doxorubicin, cisplatin, and cyclophosphamide, so it is possible to identify and characterize the genes driving the abnormalities of copy number using CGH which could lead to new therapeutic targets in ovarian cancer and possibly disturb tumor cell growth or even change sensitivity to chemotherapy. It is also possible to design microarrays that are specific to a single chromosome or chromosome arm. For example, using a chromosome 20 array with 22 cosmids, P1 phage artificial chromosome (PAC) and bacterial artificial chromosome (BAC) clones as interval markers spanning chromosome 20 at 3 Mb resolution, using this array to studying breast cancer detected SeGA in multiple regions suggest that by using a higher density array it would be possible to gain more insight into the complex chromosomal alterations in cancer genomes than previously thought. This is yet another case in which CGH has helped identify new techniques for understanding the basis of a genetic condition. Genome-wide approach CGH microarrays are usually used forregional and chromosomal anomalies that have provided us with a large amount of information, these studies are limited by the fact that they require knowledge of the regions of interest and the studies are isolated to specific regions of interest, therefore, to overcome this deficiency, arrays have been developed throughout the genome. Pollack et al. (1999) used a cDNA microarray that represented 3195 unique cDNA target clones distributed throughout the genome. This study was the first whole-genome profiling array for human cancer genomes highlighting regions of alterations in breast cancer. Genome-wide CGH using cDNA arrays has led to great strides in the field of cancer genomics. The purpose of CGH is not limited to studying the genetic basis of adverse phenotypes, for example cancer, comparative genomic hybridization has also proven useful in clinical diagnostic services. Using CGH it is possible to identify and characterize chromosomal deletions, duplications, chromosomal markers and unbalanced translocations in prenatal, postnatal and preimplantation samples. CGH has also been used to review incorrectly assigned karyotypes. CGH has the ability to precisely define chromosomal material containing unbalanced translocations and marker chromosomes, which helped to associate critical regions of the chromosome with their respective adverse phenotypic outcomes. This prognostic information is used for genetic counseling and has been shown to be helpful for couples to make a more informed pregnancy decision. Another area in which CGH has proven to be a noteworthy tool is the advancement of molecular cytogenetics for the assessment of mental retardation (Xu et al., 2002). ) as previously mentioned, CGH analysis is used to aid in the characterization of unbalanced translocations identified by band analysis and also screening for “hidden” chromosomal abnormalities in patients. Figure 2: Image of array CGH, FISH and G-banging. The image shows the application of molecular cytogenetic tools to detect chromosomal abnormalities in the case of a patient with severe mitral regurgitation, presenting with several dysmorphic facial features, prenatal growth failure, severe epilepsy, cleft palate, hirsutism, camptodactyly, and syndactyly. (With the image data above, a deletion comprising 12 clones with an estimated size of 10 Mb, located in chromosome band 2q24–31, was identified. Techniques and technologies for chromosome analysis have improved significantly over the years with the advent of modern cytogenetics, this has led to advances in clinical diagnostics, but has also provided researchers and clinicians with markers to assess prognosis and disease progression this assay is why CGH may be the most significant modern cytogenetic method to use have overcome most of the limitations of traditional cytogenetic methods addressed and even then the full potential of CGH has not been fully explored tool in detecting deletions, duplications and amplifications that contribute to neoplastic transformations as well as defining the chromosomal positions of oncogenes and tumor suppressor genes that are fundamental for the development and/or progression of tumors. At this point it is also important to note that there are limitations to CGH as well, just like any other cytogenetic methodology or technology. CGH cannot detect balanced chromosomal abnormalities such as point mutations, translocations or inversions, and it is not possible to evaluate telomeric, pericentromeric and heterochromatic regions (Knuutila et al., 2000). In order for him.