Principles of Genetics and Breeding

7.1.4.2 Fish

7.1.4.2 FISH –(Fluorescent In Situ Hybridization)

• Hybridization of specific nucleic acid sequences to chromosomes as a means of physically locating the position of genes and other markers.
• FISH is highly effective and rapid technique for use in gene mapping. First radio–isotope labeled probes were used. But it has limitations (strict regulations, long exposure time).
• Alternative method is non-radioactive labeling.
• Probes are labeled with fluorochrome dyes which fluoresce in different colours when excited by UV–light.
• Location of the probes can be visualized under Epifluoresence microscope.
• Commonly used fluro chrome are Fluroresce in isothiocyanate which fluoresces green. Rhodamine and Texas red fluoresces red and 7–amino–4- methyl cocemarin –3- acetic acid fluoresces blue.
• Through FISH technique three dimensional architecture of chromatin in interphase nuclei can be investigated. Gene expression and chromosome aberration can be studied.

Chromosome Painting is one of the application of FISH techniques.

• This technique is used to improve the accuracy of cytogenetic studies and closing the gap between cytogenetic and molecular analysis.
• A set of DNA probes derived from a single chromosome type is used for FISH.
• The direct visualization of specific chromosomes by fluorescent detection by hybridized labeled whole chromosome probes is called ‘Chromosomes painting’.
• Whole chromosomes specific probes are called ‘paints’.
• Species specific chromosomes can be identified among somatic cell hybrids.
• Chromosomal rearrangements or abnormalities can be detected for which no locus– specific probes are available.