Chromosome Banding Techniques

Chromosome banding

refers to alternating light and dark regions along the length of a chromosome, produced after staining with a dye

band

part of a chromosome that is clearly distinguishable from its adjacent segments by appearing darker or lighter with the use of one or more banding techniques

1968

year when Torbjorn Caspersson worked with plants using the highly fluorescent quinacrine mustard which produced the first reported chromosome banding patterns

1971

year when band was defined in a Paris conference as a part of a chromosome which is clearly distinguishable from its adjacent segments by appearing darker or lighter with various banding methods

importance of chromosomal banding

* allows visualization of smaller pieces of the chromosome
* identification of smaller structural chromosome abnormalities not visible on a routine analysis

positive bands

bands that show strong staining

negative bands

weakly staining bands

replication banding

most widely used function-based banding method

R-band DNA

replicated earlier than G-bands

G-bands

correspond to the condensed chromomeres of meiotic chromosomes

R-bands

correspond to the interchromomeric regions

G- and R-banding

*most commonly used techniques for chromosome identification (karyotyping)
* or identifying abnormalities of chromosome number, trans- locations of material from one chromosome to another, and deletions, inversions or amplifications of chromosome

Two ways laboratories accomplish banding methods

* optimizing the banding and staining procedures
* choosing cells with longer, less condensed chromosomes during metaphase

metaphase

phase of mitosis when dye-based chromosome banding is done

methods of dye-based chromosome banding

* Giemsa
* Reverse
* Centromere
* Quinacrine

Giemsa Banding Technique

* most widely used routine banding method in the United States
* most commonly used stain in cytogenic analysis

G-banding

staining a metaphase chromosome with a Giemsa stain

G-banding

banding techniques that require pretrating

Reverse Banding Technique

banding technique that produce a banding pattern that is the opposite or reverse of the G-banding pattern

euchromatic regions

R-band-positive regions that are the more genetically active regions of the chromosomes

R-banding

involves pretreating cells with a hot salt solution that denatures DNA that is rich in adenine and thymine

Centromere Banding Technique

techniques that stain selective chromosome regions

Torbjorn Caspersson

cytologist that developed Q banding techniques

Nor Staining

This technique selectively stains the nucleolar organizer regions (NORs) located on the satellite stalks of the acrocentric chromosomes

chromosome painting

hybridization of fluorescently labeled chromosome-specific, composite probe pools to cytological preparations

meaning of FISH

Fluorescence In Situ Hybridization

Fluorescence In Situ Hybridization

introduced the ability to highlight inidividual genes