Table of Contents
- Meaning
- Chromosome Banding Pattern
- Application of Chromosome Banding
- Frequently Asked Questions (FAQs)
Meaning
Chromosomes are made up of DNA (deoxyribonucleic acid) and proteins, located in the nucleus of every cell in the body. Genes on chromosomes are genetic instructions passed down from parents to offspring. There are 46 chromosomes in each individual, with 23 originating from the mother and 23 from the father.
Chromosome banding is the process of staining chromosomes to help researchers better understand and identify their structural composition. Chromosome banding can be compared to chromosome tie-dying. The term “chromosome banding” refers to the tagging and identifying of chromosomes by giving the appearance of various coloured bands on stained chromosomes.
Banding patterns are chromosomal patterns of bright and dark transverse bands. These bands identify where genes are located on a chromosome. The bright and dark bands are visible when the chromosome is stained with a chemical solution and examined under a microscope.
Because stains create patterns of bands down the length of the chromosome, staining of chromosomes is also known as the “banding technique.” According to one or more banding techniques, a band is the region of a chromosome that may be easily distinguished from its neighbouring sections by appearing lighter or darker.
Chromosome Banding Pattern
Chromosome banding patterns are available in various forms, such as G-banding or Giemsa Staining, C-banding, Q-banding, and R-banding.
G-banding or Giemsa Staining
Giemsa staining, commonly known as G-banding, is a cytogenetic procedure that produces a detectable karyotype by staining compressed or condensed chromosomes. This is the most basic chromosomal banding technique. Because the whole complement of chromosomes is photographed, it can be used to detect genetic disorders.
Giemsa, a visible light dye, binds DNA via intercalation. Fluorochromes are less stable than visible light dyes, which can also produce more apparent bands. Giemsa stain is a combination of anionic eosin (like eosin Y) and cationic thiazine dyes.
The cells are frozen in metaphase and then fixed, dropped, and burst after becoming turgid and bloated. Before Giemsa staining, the chromosomal spreads are processed and air-dried.
There are two types of bands observed:
Positive G-bands
The darkly stained bands are positive G-bands. These areas are hydrophobic and facilitate the precipitation of the thiazine-eosin compound. The hydrophobic proteins are responsible for hydrophobicity. These proteins maintain the condensed areas. They are primarily AT-rich regions and constitute the late replicating heterochromatin.
Negative G-bands
Negative G-bands are light-stained bands. These are less condensed early replicating euchromatin. Base pairs from GC are abundant in these areas. These areas are less hydrophobic and less conducive to the precipitation of thiazine-eosin.
C-banding
Heterochromatin is recognised by the C-banding technique, which stains heterochromatin regions of centromeres. The centromere, located close to the centre of the chromosome at the attachment point of the two chromatids, plays an essential function in the DNA division during mitosis and meiosis.
Condensed DNA is called heterochromatin, which is crucial for gene expression.
Several plant and animal species, including humans, have had their chromosomes identified using the Giemsa-C-banding technique. Since the Y chromosome in mammals is primarily heterochromatic, the C-banding method is particularly effective for identifying it.
Q-banding
Quinacrine, a yellow fluorescent stain, is used in the chromosomal banding technique known as Q-banding.
A UV lamp is required to view the fluorescent bands after it has been stained. These bands will overlap with those that appear during G-banding. Q-banding can therefore identify similar chromosomal structural anomalies as G-banding. However, the fluorescent bands in Q-banding will disappear swiftly compared to the bands that develop in G-banding. The chromosomes must therefore be examined shortly after staining.
This method is used to identify mouse and human chromosomes.
R-banding
The G-band staining technique is reversed by the cytogenetics process known as R-banding. R-banding is also known as Reverse chromosome banding.
This banding method produces a chromosomal band pattern that is the opposite of the G-band and Q-banding patterns. The dark band (AT-rich region) seen in the G-banding method appears light in the R-banding technique and vice versa.
Guanine-cytosine-rich R bands are darker in colour, and adenine-thymine-rich sections are more susceptible to heat denaturants. The method is beneficial for examining chromosomal translocations or deletions of genes involving telomeres.
Giemsa stain is also used in the R-banding procedure; however, the slide is heated in a buffer solution to 88°C before Giemsa staining. DNA denaturation results from heat.
Application of Chromosome Banding
Identifying chromosomal abnormalities and genetic diseases like Down syndrome depends greatly on chromosome banding. The additional 21st chromosome that results in Down syndrome can be found using chromosomal banding.
Visualising the evolutionary connections between chimpanzees and humans can also be accomplished with chromosome banding. Since chimpanzees and humans share many chromosomes, chromosomal banding can be used to establish the relationship between the two species and how each has evolved.
Related Links:
- Homologous Chromosome – Structure and Functions
- Chromosomal Abnormalities in Humans
- Important Notes For NEET Biology – Chromosome Structure
Main Page: BYJU’S NEET
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