Chromosome microdissection
Encyclopedia
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
from a complete chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
. The smallest portion of DNA that can be isolated using this method comprises 10 million base pair
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
s - hundreds or thousands of individual gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s.
Scientists who study chromosomes are known as cytogeneticists. 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
Homogeneously staining region
Homogeneously staining regions are chromosomal segments with various lengths and uniform staining intensity after G banding. This type of aberration is also known as Copy Number Gains or Amplification....
). Some chromosomal aberrations have been linked to cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
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
Metaphase, from the ancient Greek μετά and φάσις , is a stage of mitosis in the eukaryotic cell cycle in which condensed & highly coiled chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells...
: 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
Microscope slide
A microscope slide is a thin flat piece of glass, typically 75 by 25 mm and about 1 mm thick, used to hold objects for examination under a microscope. Typically the object is placed or secured on the slide, and then both are inserted together in the microscope for viewing...
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 (polymerase chain reaction). The scientist uses these copies to study the DNA from the unusual region of the chromosome in question.