Why karyotypes are important for biologists

For example, a woman who has premature ovarian failure may have a chromosomal defect that karyotyping can pinpoint. The test is also useful for identifying the Philadelphia chromosome. Having this chromosome can signal chronic myelogenous leukemia CML. In Klinefelter syndrome, a boy is born with an extra X chromosome.

The preparation required for karyotyping depends on the method your doctor will use to take a sample of your blood cells for testing. Samples can be taken in various ways, including:. Amniocentesis carries a very minimal risk of miscarriage. Your test results may be skewed if you are undergoing chemotherapy. Chemotherapy can cause breaks in your chromosomes, which will appear in the resulting images.

The first step in karyotyping is to take a sample of your cells. The sample cells can come from a number of different tissues. This can include:. Finally, the sample is preserved in a fixative and applied to a slide. The geneticist then stains chromosomes with one of several dyes to better visualize the distinct and reproducible banding patterns of each chromosome pair.

Following staining, the chromosomes are viewed using bright-field microscopy. A common stain choice is the Giemsa stain. Giemsa staining results in approximately — bands of tightly coiled DNA and condensed proteins arranged along all of the 23 chromosome pairs; an experienced geneticist can identify each band.

In addition to the banding patterns, chromosomes are further identified on the basis of size and centromere location. To obtain the classic depiction of the karyotype in which homologous pairs of chromosomes are aligned in numerical order from longest to shortest, the geneticist obtains a digital image, identifies each chromosome, and manually arranges the chromosomes into this pattern Figure 1.

At its most basic, the karyogram may reveal genetic abnormalities in which an individual has too many or too few chromosomes per cell. Examples of this are Down Syndrome, which is identified by a third copy of chromosome 21, and Turner Syndrome, which is characterized by the presence of only one X chromosome in women instead of the normal two.

We also get karyotypes when pregnant women choose to have testing on their unborn fetus, and the karyotype allows the providers to look at and count the chromosomes to determine whether or not the child is affected by having an extra chromosome.

Barbara Bowles Biesecker, Ph. Featured Content. Aa Aa Aa. Preparing Karyotypes from Mitotic Cells. The process of generating a karyotype begins with the short-term culture of cells derived from a specimen.

After a period of cell growth and multiplication, dividing cells are arrested in metaphase by addition of colchicine, which poisons the mitotic spindle. The cells are next treated with a hypotonic solution that causes their nuclei to swell and the cells to burst.

The nuclei are then treated with a chemical fixative, dropped on a glass slide, and treated with various stains that reveal structural features of the chromosomes. Figure 1: Chromosome banding revealed by different staining techniques. Different chromosomal staining techniques reveal variations in chromosome structure. Cytogeneticists use these patterns to recognize the differences between chromosomes and enable them to link different disease phenotypes to chromosomal abnormalities.

Giemsa banding a , Q-banding b , R-banding c and C-banding d are shown. Chromosome translocations. Nature Reviews Cancer 1, ; Stamatoullas, A. Conventional cytogenetics of nodular lymphocyte-predominant Hodgkin's lymphoma. Leukemia 21, ; Vega, H. Roberts syndrome is caused by mutations in ESCO2 , a human homolog of yeast ECO1 that is essential for the establishment of sister chromatid cohesion.

Nature Genetics 35, All rights reserved. Figure Detail. Organizing Chromosomes in Karyograms for Review. Using Karyograms to Detect Chromosomal Abnormalities. References and Recommended Reading Caspersson, T. Nature Genetics 12 , — link to article Strachan, T. Wiley, New York, Tjio, J. Hereditas 42 , 1—6 Trask, B. Article History Close. Share Cancel.

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