User:Chamnessra/Molecular cytogenetics

(original article unedited - retrieved 3/4/20)

Molecular cytogenetics involves the combination of molecular biology and cytogenetics; using various reagents, molecular cytogenetics seeks to properly distinguish normal and cancer-causing cells. Molecular cytogenetics is a useful tool for the diagnosing and treatment of various malignancies such as brain tumors, haematological malignancies, etc. It includes a series of techniques referred to as fluorescence in situ hybridization, or FISH, in which DNA probes are labeled with different colored fluorescent tags to visualize one or more specific regions of the genome. FISH can either be performed as a direct approach to metaphase chromosomes or interphase nuclei. Alternatively, an indirect approach can be taken in which the entire genome can be assessed for copy number changes using virtual karyotyping. Virtual karyotypes are generated from arrays made of thousands to millions of probes, and computational tools are used to recreate the genome in silico.

Fluorescence in situ hybridization (FISH)[edit]
FISH images of chromosomes from dividing orangutan (left) and human (right) cells. Yellow probe shows 4 copies of a region in the orangutan genome and only 2 copies in human. Fluorescence In Situ Hybridization maps out single copy or repetitive DNA sequences through localization labeling of specific nucleic acids. The technique utilizes different DNA probes labeled with fluorescent tags that bind to one or more specific regions of the genome. Signals from the fluorescent tags can be seen with microscopy, and mutations can be seen by comparing these signals to healthy cells. FISH can be applied directly to chromosomes in actively dividing or non-dividing cells to observe changes in genetic composition at a molecular level.

FISH chromosome in-situ suppression hybridization allows the study cytogenetics in pre- and postnatal samples. This technique labels all individual chromosomes at every stage of cell division to display structural and numerical abnormalities that may arise throughout the cycle.

Alternatively, an indirect approach can be taken in which the entire genome is be assessed for copy number changes. This technique is referred to as virtual karyotyping. Virtual karyotypes are generated from arrays that hold thousands to millions of probes, and computational tools are used to analyze and assemble the genome in silico.

(Edited - 4/2/20)

Molecular cytogenetics combines two disciplines, molecular biology and genetics, and involves the analyzation of chromosome structure to help distinguish normal and cancer-causing cells. Human cytogenetics began in 1956 when it was discovered that normal human cells contain 46 chromosomes. However, the first microscopic observations of chromosomes were reported by Arnold, Flemming, and Hansemann in the late 1800's. Their work was ignored for decades until the actual chromosome number in humans was discovered as 46. In 1879, Arnold examined sarcoma and carcinoma cells having very large nuclei. Today, the study of molecular cytogenetics can be useful in diagnosing and treating various malignancies such as hematological malignancies, brain tumors, and other precursors of cancer. The field is overall focused on studying the evolution of chromosomes, more specifically the the number, structure, function, and origin of chromosome abnormalities.

Technological advances have also propelled this field. Cytogenetic analysis has improved drastically over the years and allows for many strategies for cytogenetic analysis to keep up with the growing field. This includes a series of techniques referred to as fluorescence in situ hybridization (FISH) which detects subtle alterations in chromosome composition. Introduced in the 1980's, FISH uses probes with complimentary base sequences to locate the presence or absence of the specific DNA regions you are looking for. This technique labels all individual chromosomes at every stage of cell division to display structural and numerical abnormalities that may arise throughout the cycle. This is done with a probe that can be locus specific, centromeric, telomeric, and whole-chromosomal. This technique is typically preformed on interphase cells and paraffin block tissues. FISH maps out single copy or repetitive DNA sequences through localization labeling of specific nucleic acids. The technique utilizes different DNA probes labeled with fluorescent tags that bind to one or more specific regions of the genome. Signals from the fluorescent tags can be seen with microscopy, and mutations can be seen by comparing these signals to healthy cells.For this to work, DNA must be denatured using heat or chemicals to break the hydrogen bonds; this allows hybridization to occur once two samples are mixed. The florescent probes create new hydrogen bonds, thus repairing DNA with their complimentary bases, which can be detected through microscopy. FISH allows one to visualize different parts of the chromosome at different stages of the cell cycle. FISH can either be performed as a direct approach to metaphase chromosomes or interphase nuclei. Alternatively, an indirect approach can be taken in which the entire genome can be assessed for copy number changes using virtual karyotyping. Virtual karyotypes are generated from microarrays made of thousands to millions of probes, and computational tools are used to recreate the genome in silico.

FISH chromosome in-situ hybridization allows the study cytogenetics in pre- and postnatal samples and is also widely used in cytogenetic testing for cancer. While cytogenetics is the study of chromosomes and their structure, cytogenetic testing involves the analysis of cells in the blood, tissue, bone marrow, or fluid to identify changes in chromosomes of an individual. This was often done through karyotyping, and is now done with FISH. This method is commonly used to detect chromosomal deletions or translocations often associated with cancer. FISH is also used for melanocytic lesions, distinguishing atypical melanocytic or malignant melanoma. Comparative genomic hybridization (CGH), derived from FISH, is an another example of molecular cytogenetic testing that detects chromosomal copy number variants. This method uses two genomes, a sample and a control, which are labeled fluorescently to distinguish them. They are denatured and then mixed together, and then hybridization of metaphase chromosomes can occur. This technique shows the loss or gain of genetic material of chromosomes as well as copy number variants. CGH differs because it does not require a specific target or previous knowledge of the genetic region being analyzed. CGH can also scan an entire genome relatively quickly for various chromosome imbalances, and this is helpful in patients with underlying genetic issues and when an official diagnosis is not known. This often occurs with hematological cancers.

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