FISH(Fluorescent in situ hybridization)

FISH(FLORESCENCE IN SITU HYBRIDIZATION)
  • Fluorescpresence and location of a region of DNA or RNA within morphologically preserved chromosoment in situ hybridization (FISH) is a molecular cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity.
  • Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes.
  • Used to identify the e preparations, fixed cells or tissue sections

FISH PROCEDURE:
  • Denature the chromosomes
  • Denature the probe
  • Hybridization
  • Fluorescence staining
  • Examine slides in the dark
DIAGNOSTIC APPLICATIONS OF FISH
  • Prenatal Diagnosis
  • Cancer Diagnosis
  • Gene Mapping
  • Molecular Cytogenetic of Birth defects and mental retardation.
  • Examples of diseases that are diagnosed using FISH include Prader-Willi syndrome, Angelman syndrome, 22q13 deletion syndrome, chronic myelogenous leukemia, acute lymphoblastic leukemia, Cri-du-chat, Velocardiofacial syndrome, and Down syndrome.
  • Identification of specific chromosomal abnormalities.
  • Study of 3D chromosome organization in interphase nuclei
  • Monitoring the sucess of bone marrow transplantation.
  • FISH on sperm cells is indicated for men with an abnormal somatic or meiotic karyotype as well as those with oligozoospermia, since approximately 50% of oligozoospermic men have an increased rate of sperm chromosome abnormalities.
TYPES OF PROBE USED IN FISH
  • Locus Specific probe:
  • Centromere probe
  • Telomere probe
  • Whole Chromosome probe.
ADVANTAGES AND LIMITATIONS OF FISH

Advantages:
  • FISH is able to detect many small deletions, duplications and rearrangements that are not visible with standard microscope analysis (Karyotype)
  • Chromosomes do not have to be in the metaphase stage for accurate diagnosis.Even though interphase and prophase chromosomes cannot be clearly visualised themselves,the number of hybridization signals can still be counted accurately.
Limitations:
  • FISH testing does not usually screen all chromosomes for changes. Most FISH probes are specific for one particular deletion or duplication within one band of one chromosome so it will only find what it is looking for.
  • FISH probes are only available for the most well characterised deletion and duplication syndromes.
Exam Question
  • Gene mapping,Study of 3D chromosome organization in interphase nuclei ,Monitoring the success of bone marrow transplantation ,etc are the applications of FISH.

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