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 has been recognized, several studies have been carried out using cytological and genetic methods, using data collected by genetic procedures as well as observations made using cytological techniques. This dual approach to heredity problems has been called cytogenetics. Cytogenetics has provided an understanding of the genetic basis of diseases as well as a powerful tool for diagnosing genetic diseases. Some traditional cytogenetic techniques are chromosome banding and fluorescent in situ hybridization (FISH). In chromosome banding, chromosomes are treated with different chemicals to color them and interpretations are made from how the chromosomes stain, depending on the dyes used it can be G bands, Q bands , C bands or R bands. Say no to plagiarism. Get a tailor-made essay on 'Why violent video games should not be banned'?Get the original essayIn FISH, a nucleic acid probe is conjugated to a fluorescent dye, which is then used to detect complementary sequences on chromosomes in metaphase or in nuclei in interphase. After hybridization, the location of bound probes is detected and analyzed using fluorescence microscopy and digital imaging technology. The traditional techniques mentioned above are powerful tools on which the foundations have been built, but they have their limitations, for example, chromosome bands are unable to detect deletions smaller than 5 Mb, i.e. microdeletions and in FISH, appropriate probes must be selected in order to identify chromosomal aberrations. To overcome these shortcomings, several advances have been made in the field and these technological advances have helped improve our ability to study and define cellular processes at the molecular level, which has benefited both scientists and clinicians. Few new FISH based technologies are Reverse FISH, Multiplex FISH (M-FISH), Spectral Karyotyping (SKY), Comparative Genomic Hybridization Analysis (CGH) and Matrix or Microarray Analysis – CGH (M- CGH). Instead of discussing all modern cytogenetic methods and their impact on identifying disease bases and clinical diagnostic services, this essay will focus on comparative genomic hybridization and its implications. Cytogenetic technologies have had a major impact on the field of medicine and in particular in reproductive medicine and oncology, they have made it possible to understand and analyze the frequencies at which chromosomal aberrations occur during gametogenesis, embryonic development and tumor development. We are now able to better understand and detect genetic abnormalities associated with tumor origins, tumor progression, spontaneous abortions and congenital anomalies. CGH technology allows us to identify and map genomic regions for any chromosomal loss or gain during 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 based on chromosomal location throughout the sequence. the entire genome. There are two ways to perform CGH, either using the direct method orusing the indirect method. For the direct method we use fluorochromes, while for the indirect method we use haptens. The use of haptens could be more beneficial in some cases as they are both cost effective. and more flexible. In case a reference standard is needed for data analysis, CGH is performed with a different labeled normal DNA. To perform more detailed analysis, CGH is coupled with a sensitive monochrome CCD (cooled charge coupled device) 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 which are being studied, in the case of chromosomal duplication or gene amplification in tumor DNA, there would be an increase in green/red ratios whereas in chromosomal deletions there would be a decrease. Microarray-based comparative genomic hybridization (array CGH) is capable of combining the advantages of molecular diagnostics as well as traditional cytogenetic techniques and the advancement of the field of cytogenetics. Studies performed on individuals with developmental delay and dysmorphic features have shown that array CGH is capable of causing chromosomal aberrations such as duplications, deletions, amplifications, and aneuploidies. In the case of individuals with normal results before cytogenetic testing, detection rates for chromosomal aberrations were 5-17%, copy number variants (CNVs) can also be identified. Array CGH is a powerful tool that has the potential to be a diagnostic tool for identifying visible and submicroscopic chromosomal abnormalities in mental retardation and other developmental disorders. Tumor Genetics Cancer can be aptly described as a disease resulting from genomic instability and given that CGH is designed to identify segmental genomic alterations, it is a suitable tool for studying the genetic basis of cancer and chromosomal abnormalities. which are associated with it. 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 being developed to further improve the resolution of CGH 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 to use HER2/neu/erB2 for antibody mediated therapy (Herceptin ) and gene therapy mediated by E1 A. In the study conducted by Kudoh et al. , they were able to show that the increased presence of copy number at 1q21 and 13q13 correlated with the lack of response to the chemotherapy regimen based on doxorubicin, cisplatin and cyclophosphamide. It is therefore possible to identify and characterize the genes causing copy number abnormalities using CGH which could lead to new therapeutic targets in ovarian cancer and possibly disrupt the growth of tumor cells or even modify sensitivity to chemotherapy. It is also possible to design microarrays specific to a single chromosome or a chromosome arm. For example, using a chromosome 20 array with 22 cosmid clones, phage P1 artificial chromosomes (PACs), and bacterial artificial chromosomes (BACs) as interval markers covering chromosome 20 at 3 MB resolution, in using this network tostudying breast cancer, he detected SeGAs in several regions suggesting that by using a higher density array it would be possible to obtain more information about the complex chromosomal alterations of cancer genomes than is possible. thought before. This is another example in which CGH has helped identify new techniques for understanding the basis of a genetic disease. Genome wide approach CGH microarrays are generally used for regional and chromosomal abnormalities which have provided us with a lot 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 gap, genome-wide arrays have been developed. Pollack et al. (1999) used a cDNA array representing 3,195 unique cDNA target clones distributed throughout the genome. This study was the first round of genome-wide profiling of human cancer genomes, highlighting regions of alterations in breast cancer. Genome-wide CGH using cDNA templates has enabled significant advances in the field of cancer genomics. The scope of CGH is not limited to the study of 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, marker chromosomes and unbalanced translocation in prenatal, postnatal and preimplantation samples. CGH has also been used to revise misassigned karyotypes. CGH has the ability to precisely define chromosomal material containing unbalanced translocations and marker chromosomes, which allowed critical regions of the chromosome to be associated with the respective adverse phenotypic outcomes. This prognostic information is used for genetic counseling and has been shown to be beneficial in allowing couples to make a more informed decision regarding pregnancy. Another area in which CGH has proven to be a remarkable tool is the advancement of molecular cytogenetics to assess mental retardation (Xu et al., 2002) as previously mentioned, CGH analysis is used to further characterize mental retardation. unbalanced translocations identified using banding analysis and also for screening for “hidden” chromosomal abnormalities in patients. Figure 2: Image of CGH, FISH and G-banging array. The image shows the application of molecular cytogenetic tools to detect chromosomal abnormalities in the case of a patient with severe MR, presenting with several dysmorphic facial features, prenatal growth deficiency, severe epilepsy, cleft palate, hirsutism, camptodactyly and syndactyly. (With the data in the image above, a deletion spanning 12 clones with an estimated size of 10 MB was identified, located on chromosome band 2q24-31. Chromosome analysis techniques and technologies have improved significantly Over the years with the advent of modern cytogenetics, this has led to advances in clinical diagnosis, but also provided researchers and clinicians with markers to assess prognosis and disease progression. which we discuss at length about comparative genomic hybridization in this essay is that CGH could probably be the most important modern cytogenetic method for diagnosis having overcome most of the limitations of traditional cytogenetic methods and even then the full potential. of CGH has not been fully explored. CGH has been shown to be..