Karyotype Medical Definition

Today, G-band karyograms are commonly used to diagnose a variety of chromosomal abnormalities in individuals. Although the resolution of chromosomal changes detectable by karyotyping is typically a few megabases, this may be sufficient to diagnose certain categories of abnormalities. For example, aneuploidy, which is often caused by the absence or addition of a chromosome, is easily detected by karyotype analysis. Cytogeneticists can also often detect deletions or insertions that are much more subtle than deviations from normal bands. Similarly, karyotype translocations are often easily recognizable. The study of the human karyotype took many years to clarify the most fundamental question: how many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonies and 48 in oogony, resulting in a sex determination mechanism XX/XO. [12] In 1922, Painter was not sure whether the diploid man was 46 or 48 years old, at first he was in favor of 46,[13] but revised his opinion from 46 to 48, and he rightly insisted that humans have an XX/XY system. [14] Given the techniques of the time, these results were remarkable. A karyotype test looks at blood or body fluids for abnormal chromosomes. Adults, children or developing fetuses may need this test if they are at risk for certain genetic diseases. Before deciding on a karyotype test, talk to your doctor about genetic counseling. Counselling can help you weigh the risks and benefits of chromosomal analysis.

The sample is placed in a special dish or tube and allowed to grow in the laboratory. The cells are then removed from the new sample and stained. The laboratory specialist uses a microscope to examine the size, shape and number of chromosomes in the cell sample. The colored sample is photographed to show the arrangement of chromosomes. This is called a karyotype. Instead of the usual genetic repression, some organisms engage in large-scale elimination of heterochromatin or other types of visible karyotype adaptation. The work took place in 1955 and was published in 1956. The human karyotype consists of only 46 chromosomes. [16] [17] Other great apes have 48 chromosomes. It is now known that human chromosome 2 is the result of an end-to-end fusion of two ancestral monkey chromosomes. [18] [19] A karyotype is a preparation of the complete set of metaphase chromosomes in the cells of a species or in a single organism, sorted by length, centromere position and other characteristics, and for a test that detects this complement or counts the number of chromosomes.

[1] [2] [3] [4] Karyotyping is the process by which a karyotype is made from photographs of chromosomes to determine an individual`s chromosomal complement, including the number of chromosomes and any abnormalities. Cleveland Clinic is a non-profit academic medical center. Advertising on our website helps support our mission. We do not endorse products or services that are not provided by the Cleveland Clinic. The next step took place after the development of genetics at the beginning of the 20th century. It was discovered that chromosomes (which can be observed by karyotype) carried genes. Lev Delaunay [ru] seems to have been the first to define karyotype as the phenotypic appearance of somatic chromosomes as opposed to their genetic content in 1922. [7] [8] The subsequent history of the concept can be traced back to the work of C. D. Darlington[9] and Michael J.D. White.

[3] [10] Last reviewed by a doctor at the Cleveland Clinic on 06.03.2021. A karyotype test uses blood or body fluids to analyze your chromosomes. Chromosomes are the parts of our cells that contain genes made up of DNA. You inherit genes from your parents. Genes determine your characteristics such as eye and skin color. Different types of health care providers may take blood or fluid samples, depending on the karyotype test you need. Pathologists (health care providers who examine blood and tissues) or geneticists trained in chromosomal analysis examine blood or fluid in a laboratory. The blood collection process for a standard karyotype test only takes a few minutes. You can get the test at your doctor`s office, a hospital or a laboratory. A health care provider called a lab technician usually takes blood samples.

Karyotypes are arranged with the short arm of the chromosome at the top and the long arm at the bottom. Some karyotypes call the short and long arms p and q, respectively. In addition, regions and subregions of different colors are given numeric designations from proximal to distal on chromosomal arms. For example, Cat Cry syndrome involves a deletion on the short arm of chromosome 5. It is written 46,XX,5p-. The critical region for this syndrome is the deletion of p15.2 (the locus on the chromosome), writes 46,XX,del(5)(p15.2). [64] Karyotype. The karyotype is one of the characteristics of any species. To create a karyotype, scientists take a picture of a cell`s chromosomes, cut them out, and organize them as guidelines based on the size, stripe patterns, and positions of the centromeres.

The karyotype describes the amount of chromosomes and morphology of an organism under an optical microscope. Derivation and study of karyotypes are part of cytogenetic studies. In normal diploid organisms, autosomal chromosomes are present in two copies. Karyotypes can be used for many purposes, such as chromosomal nitration studies in prenatal diagnosis or tumor studies. Also to understand cellular functions, taxonomic relationships and information about past evolutionary events. The typical human karyotype contains 22 pairs of autosomal chromosomes and one pair of sex chromosomes. The most common karyotypes for a woman contain two X chromosomes and are called sex XX. Males usually have both an X chromosome and a Y chromosome, called the XY gender.

Karyotype: A standard chromosomal complement arrangement prepared for chromosomal analysis. A normal female karyotype would include each of the 22 pairs of autosomes (non-sex chromosomes) arranged in numerical order, as well as the two X chromosomes. A spectacular example of variability between closely related species is the muntjac, studied by Kurt Benirschke and Doris Wurster. The diploid number of Chinese Muntiacus reevesi, Muntiacus reevesi, was found at 46, all teleloccentric. When they looked at the karyotype of the closely related Indian muntjac, Muntiacus muntjac, they were amazed that it had female = 6, male = 7 chromosomes. [33] Six different characteristics of karyotypes are commonly observed and compared:[22] The study of karyotypes is made possible by staining. Normally, a suitable dye, such as Giemsa,[20] is applied after cells are stopped by a solution of colchicine during cell division, usually metaphase or prometaphase when they are most condensed. In order for Giemsa staining to adhere correctly, all chromosomal proteins must be digested and eliminated. In humans, white blood cells are most often used because they are easily made to divide and grow in tissue culture. [21] Sometimes observations can be made on undivided (interphased) cells. The sex of an unborn fetus can be predicted by observing interphase cells (see amniocentesis and Barr`s body).

Abnormal karyotype test results could mean that you or the fetus have unusual chromosomes. This may indicate genetic diseases and disorders such as: Britannica.com: Encyclopedia articles on karyotyping Karyotypes are made from mitotic cells that have been blocked in the metaphase or prometaphase part of the cell cycle when chromosomes take on their most condensed conformations. A variety of tissue types can be used as a source for these cells. For cancer diagnoses, typical samples are tumor biopsies or bone marrow samples. For other diagnoses, karyotypes are often generated from peripheral blood samples or skin biopsy. For prenatal diagnosis, samples of amniotic fluid or chorionic villi are used as a cellular source. The number of chromosomes in the karyotype between (relatively) unrelated species is highly variable. The lowest record is held by the nematode Parascaris univalens, where haploid n = 1; and an ant: Myrmecia pilosula.

[34] The high record would be somewhere among ferns, with the tongue fern Ophioglossum leading with an average of 1262 chromosomes. [35] The main marks for animals could be the short-nosed sturgeon Acipenser brevirostrum with 372 chromosomes. [36] The existence of excess chromosomes or B means that the number of chromosomes can vary even within a cross-population; And aneuploids are another example, although in this case they would not be considered normal members of the population. Medterms Medical Dictionary A-Z Karyotype List / Definition Although DNA replication and transcription in eukaryotes is highly standardized, this is not true for their karyotypes, which are highly variable. There are differences between species in number of chromosomes and detailed organization, despite their construction from the same macromolecules. This variation forms the basis of a number of evolutionary cytology studies. Molecular cytogenetics is a dynamic discipline and new diagnostic methods are constantly being developed. If these new technologies are implemented clinically, we can expect cytogeneticists to be able to make the leap from karyotype to gene with increasing efficiency. Some people choose to talk to a genetic counselor before getting a karyotype test. Test results can have profound emotional effects.

This is especially true for parents who may discover that the fetus has a genetic disease. This type of test is your decision, so it`s important to weigh the risks and benefits before making a decision. Although much is known about karyotypes at the descriptive level and it is clear that changes in karyotype organization have had an impact on the evolutionary course of many species, it is not clear what the general significance might be.