A karyotype is an image of an organism’s chromosomes, used to evaluate abnormalities and variations. Samples are taken, stained, and photographed during cell division. Karyotypes can be ordered for various reasons, including genetic counseling and research.
A karyotype is an image that depicts the chromosomes of an organism. The term is also used to refer more generally to the complement of chromosomes found in a healthy representative of a species. Humans, for example, have 46 chromosomes in 23 pairs. Karyotypes can vary dramatically between species and sometimes within a species, and researchers are constantly discovering more information about them. Thanks to improvements in microscopy and scientific imaging, it is possible to generate very detailed and high-quality karyotypes for study.
To generate an image of chromosomes, a sample is taken, stained, and photographed, usually during cell division when the chromosomes are highly visible. A geneticist arranges chromosomes, matching pairs and arranging them into rows so they can be clearly seen. Depending on the type of staining and imaging used, different levels of detail are visible. A karyotype can be a cell from a living adult organism, a child, or cells taken from a developing fetus for diagnostic testing.
When a geneticist examines a karyotype, they evaluate the image to look for abnormalities. The shape, size, and number of chromosomes can vary, and these variations can provide clues to a medical problem. For example, if a human karyotype reveals that a patient has three copies of the 21st chromosome, instead of two, the patient is diagnosed with Trisomy 21, also known as Down syndrome. Researchers can also compare chromosome bands in the patient to look for abnormalities and variations.
Some organisms demonstrate genetic mosaicism, in which the genetic material varies from cell to cell. For this reason, when a karyotype is prepared, the geneticist can use samples of different cells to determine whether or not a genetic variation is consistent throughout the body. The geneticist may also request further testing of specific chromosomes to look for genetic material of interest or concern, such as genes that cause inherited diseases.
Karyotypes can be ordered for a variety of reasons. When people visit a genetic counselor to get information about genetic conditions, the counselor may obtain a karyotype as part of the patient’s evaluation. Karyotypes are also used by researchers interested in various genetic conditions and variations between species. Many people have seen a karyotype, even though they may not be aware of it, because karyotypes are often used to illustrate genetics textbooks and articles about genetic conditions.
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