Chromosome Painting | Zoology Optional Notes for UPSC PDF Download

Chromosome Painting Technique

Purpose of Chromosome Painting

1. Visualizing individual chromosomes in metaphase or interphase stages.
2. Identifying numerical and structural chromosomal aberrations with high sensitivity and specificity.
3. Color karyotyping, achieved through simultaneous hybridization of multiple chromosome painting probes, each tagged with a specific light-emitting fluorochrome.

Multicolor FISH (M-FISH)
Chromosome painting is sometimes referred to as M-FISH or multicolor FISH due to its ability to detect both simple and complex chromosomal rearrangements. It provides valuable insights that conventional cytogenetic banding techniques may not.

Historical Development
Chromosome painting was independently developed by research teams at Lawrence Livermore National Laboratories and Yale University. Initially, chromosome-specific phage libraries were used as probes, which had some limitations. Subsequently, plasmid libraries with improved insert-to-vector ratios enhanced the quality of chromosome painting.

Applications of Chromosome Painting

• Efficient screening for chromosome abnormalities.
• Testing chemicals for mutagenicity.
• Detecting rearrangements associated with tumors.
• Identifying the origin of marker chromosomes not identifiable through standard banding techniques.
• Comparative cytogenetics to understand chromosome changes during species evolution.

Comparative Cytogenetics
Chromosome painting aids in the identification of homologous chromosome segments in different species and mapping probes for chromosome rearrangements. This technique has been applied to the complete karyotyping of various mammals, shedding light on chromosome changes during species evolution.

Chromosome Painting Probes

• Supplied in liquid format in five-test kit.
• Provided with DAPI counter stain for microscopy.
• Rapid and simple protocol involving co-denaturation of FISH probe and target DNA.

Reverse Chromosome Painting
Reverse chromosome painting is a technique to verify the origin of marker chromosomes not identifiable by standard techniques. It involves micro-dissection, in vitro DNA amplification, and fluorescence in situ hybridization (FISH) with labelled PCR products.

How Chromosome Painting Works

1. Chromosomes sorted by flow cytometry.
2. DNA from one chromosome labeled with fluorescent dye through FISH.
3. Labeled DNA paints the chromosome and allows homologous regions in other species to be identified.
4. Homologous regions appear in the same color, aiding in the tracking of rearrangements during species divergence.

Detecting Chromosome Aberrations
Chromosome painting can detect reciprocal translocations, where two chromosomes exchange parts of their DNA, and is particularly useful for identifying such complex chromosomal abnormalities.

Commonalities Across Species
Patterns of linked chromosome regions in different mammalian species help identify genomic commonalities and understand chromosome evolution.

Chromosome Walking

Procedure
Chromosome walking involves a series of colony hybridizations, starting with a known cloned fragment within the region of interest. This fragment is used as a probe to identify adjacent sequences in overlapping clones. The identified clones are then used as probes to locate further adjacent sequences, allowing researchers to "walk" along the chromosome from the initial fragment.

Purpose
Chromosome walking is a powerful method for detecting translocations and identifying DNA sequences along a chromosome. It aids in understanding genetic rearrangements and structural variations.