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Chromosomal bands are created through differential staining techniques to study chromosomes under a microscope during cell division. Different techniques, such as G-band and C-band, allow for the study of different aspects of chromosome banding patterns. Giemsa stain is commonly used and creates chromosomal banding patterns with dark areas rich in adenine and thymine, while pale areas are rich in guanine and cytosine. Karyotype can be determined by counting the number of bands.
Chromosomal bands are the transverse bands that appear on chromosomes as a result of various differential staining techniques. Differential stains impart colors to tissues, so they can be studied under a microscope. Chromosomes are thread-like structures of long strands of deoxyribonucleic acid (DNA), which coil into a double helix and are made up of genetic information, or genes, which are arranged transversely along the length.
To analyze chromosomes under a microscope, they must be stained when they are undergoing cell division during meiosis or mitosis. Mitosis and meiosis are cell division processes that are divided into four stages. These phases are prophase, metaphase, anaphase, and telophase.
Cryptogenetics is the study of cell function, cell structure, DNA and chromosomes. It employs various techniques to stain chromosomes, such as G-band, R-band, C-band, Q-band, and T-band. Each staining technique allows scientists to study different aspects of chromosome banding patterns.
Giemsa banding, also known as G-banding, allows scientists to study chromosomes in the metaphase stage of mitosis. Metaphase is the second stage of mitosis. In this stage the chromosomes are aligned and attached to the centers or their centromeres and each chromosome appears in the shape of an X.
Before applying the stain to chromosomes, they must first be treated with trypsin, which is a digestive fluid found in many animals. The trypsin will begin digesting the chromosomes, allowing them to better receive the Giemsa stain. Giemsa stain was discovered by Gustav Giemsa and is a mixture of methylene blue and the red acid dye, eosin. Q-banding uses quinicrine, which is a mustard-like solution. It produces results very similar to Giemsa, but has fluorescent qualities.
DNA is composed of four basic acids that appear in pairs: adenine paired with thymine and cytosine with guanine. Giemsa stain creates chromosomal banding patterns with dark areas rich in adenine and thymine. The pale areas are rich in guanine and cytosine. These areas replicate early and are euchromatic. Euchromatic is a genetically active area that stains very lightly with dye treatments.
Reverse-banding, or R-banding, produces chromosomal banding patterns that are the opposite of G-banding. The darker areas are rich in guanine and cytosine. It also produces euchromatic parts with high concentrations of adenine and thymine.
With C-banding, Giemsa stain is used to study the constitutive heterochromatin and centromere of a chromosome. Constitutive heterochromatins are areas near the center of the chromosome that contain highly condensed DNA that tend to be transcriptionally silent. The centromere is the region in the center of the chromosome.
T-banding allows scientists to study the telomeres of a chromosome. Telomeres are the caps found on each of the chromosomes. They contain repetitive DNA and are intended to prevent any deterioration.
Once the chromosomes have been stained with Giemsa, researchers can clearly see the alternating patterns of dark and light chromosome bands that are produced. By counting the number of bands, the karyotype of a cell can be determined. Karyotype is the characterization of chromosomes for a species based on size, type and number.
