Humans possess 24 distinct types of chromosomes.
Chromosome banding techniques are used to distinguish between different types of chromosomes. Different banding techniques are used to highlight different regions of the chromosomes, and the dark and light bands indicate stained and unstained regions respectively. Chromosome banding techniques include: G banding, C banding, Q banding and R banding.
G Banding
The G banding chromosomal technique is used to identify structural abnormalities. This technique is undertaken by dehydrating the slides containing the chromosomes, treating them with the enzyme trypsin, and then staining them. Equipment recommended by Wildlife Web to carry out this technique includes: glass Coplin jars with lids; 5 ml and 10 ml serological pipettes and bulbs; timer; staining rack; plastic squirt bottle; a dehydrating oven set to 95 degrees centigrade; slide racks; and a slide warming tray set at 60 degrees centigrade. When the chromosomes are stained, each pair produces a distinctive pattern of light and dark bands; the dark bands are named G bands. They correlate to repetitive DNA sequences and base-pair composition.
C Banding
C banding is used to specifically stain the centromeric regions, which is the area of DNA found near the center of a chromosome in which two sister chromotids are closest in contact. It also is designed to stain other regions that contain the constitutive heterochromatin, which is the DNA and proteins that make up the nucleus. C banding stains darkly and requires the following equipment, according to Wildlife Web: a circulating water bath set at 65 degrees centigrade; nine centimeter circles of Whatman #1 filter paper; four glass Coplin jars with lids; slide warmer; timer; and squirt bottle filled with distilled water.
Q Banding
Q banding involves treating chromosomes with a fluorescent stain, using fluorescent microscopy, called quinicrine mustard solution, which identifies specific chromosomes and structural rearrangements. It is particularly useful for distinguishing Y bodies in interphase nuclei, the Y chromosome and other polymorphisms. Using this technique, some bands appear fluorescent, while the dim bands that appear correspond to Q bands. Equipment recommended by Wildlife Web for Q banding includes: three one liter bottles; Mettler analytical balance; eight Coplin jars; clean coverslip; 10 ml serological pipette; and a 50 ml beaker.
R Banding
Also called Giemsa Reverse banding, R banding requires the slides containing the chromosome in question to be incubated in a hot phosphate buffer, followed by Giemsa, a type of staining often used in the identification of malaria and other parasites. The chromosome pattern that this produces possesses darkly stained R bands and pale G bands, staining the bands in reverse. A technique using acridine orange (AO) to achieve reverse banding patterns for chromosomes is now favored. AO binds to the DNA by intercalation and provides a uniform fluorescence along the chromosome arms.
