Chromosome microdissection is a technique that physically removes a large section of
DNA from a complete
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
. The smallest portion of DNA that can be isolated using this method comprises 10 million
base pairs - hundreds or thousands of individual
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s.
Scientists who study chromosomes are known as
cytogeneticist
Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis an ...
s. They are able to identify each chromosome based on its unique pattern of dark and light bands. Certain abnormalities, however, cause chromosomes to have unusual banding patterns. For example, one chromosome may have a piece of another chromosome inserted within it, creating extra bands. Or, a portion of a chromosome may be repeated over and over again, resulting in an unusually wide, dark band (known as a
homogeneously staining region). Some chromosomal aberrations have been linked to
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
and inherited genetic disorders, and the chromosomes of many tumor cells exhibit irregular bands. To understand more about what causes these conditions, scientists hope to determine which genes and DNA sequences are located near these unusual bands. Chromosome microdissection is a specialized way of isolating these regions by removing the DNA from the band and making that DNA available for further study.
To prepare cells for chromosome microdissection, a scientist first treats them with a chemical that forces them into
metaphase
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, align ...
: a phase of the cell's life-cycle where the chromosomes are tightly coiled and highly visible. Next, the cells are dropped onto a
microscope slide
A microscope slide is a thin flat piece of glass, typically 75 by 26 mm (3 by 1 inches) and about 1 mm thick, used to hold objects for examination under a microscope. Typically the object is mounted (secured) on the slide, and then b ...
so that the nucleus, which holds all of the genetic material together, breaks apart and releases the chromosomes onto the slide. Then, under a microscope, the scientist locates the specific band of interest, and, using a very fine needle, tears that band away from the rest of the chromosome. The researcher next produces multiple copies of the isolated DNA using a procedure called
PCR PCR or pcr may refer to:
Science
* Phosphocreatine, a phosphorylated creatine molecule
* Principal component regression, a statistical technique
Medicine
* Polymerase chain reaction
** COVID-19 testing, often performed using the polymerase chain r ...
(
polymerase chain reaction
The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...
). The scientist uses these copies to study the DNA from the unusual region of the chromosome in question.
References
* Scalenghe F, Turco E, Edstrom JE, Pirrotta V, Melli M.: Microdissection and cloning of DNA from a specific region of Drosophila melanogaster polytene chromosomes. Chromosoma. 1981;82(2):205-16.
External links
National Institutes of HealthNational Institutes of Health Laser Microdissection Core Facility
Applied genetics