Karyotyping: What is it and why is it important?

The takeaway: Karyotyping is an important genetic test that can find anomalies in chromosomes, and it is the basis for more advanced and developing techniques in genetic research.

Karyotyping is both a test and a process that is important in genetic research. This molecular technique was first used in the 1950s but has become more precise and useful in the decades since then. Let’s look at karyotyping in more detail. While some terms are used loosely, a karyotype is how a set of chromosomes look in a cell, karyotyping is the process of using a karyotype to determine how an organism’s chromosomes appear, and a karyogram is a graphic representation of a karyotype.

Let’s look at this genetic technique in more detail. 

When was karyotyping discovered and first used?

The first karyotyping techniques discovered simple anomalies in chromosomes, such as a missing copy of a chromosome or duplicates, and chromosomal conditions such as Down syndrome were discovered using this method. In the following decades, new techniques, including positional cloning, were developed that made it possible to find the gene responsible for a given condition and determine how it was related to the condition—and how the condition presented physically.

As the study of genetics matured in the 1990s, researchers gained a better understanding of how some genetic disorders could be caused by structural changes to a genome, with the changes frequently the result of copy number variants—duplicate copies of a gene or a missing gene copy in whole or part. For example, in Down syndrome, an individual has an extra copy of chromosome 21, while in Charcot-Marie-Tooth disease, there is most often a duplicate in a precise region in chromosome 17.

In recent years, new approaches to karyotyping have been developed. These approaches speed up the turnaround time needed for an investigation and can offer much higher resolutions. These approaches include G-banding (a DNA staining technique that allows a researcher to visually investigate the structure of chromosomes in the nucleus of a cell) and array-based karyotyping (this method provides the ability to detect unbalanced chromosomal abnormalities. Next generation sequencing has emerged as an alternative technology to karyotyping and can accurately and precisely detect copy number variations.

What is a karyotype?

A karyotype is the complete set of chromosomes or an organism, though the term can also be used to refer to a lab-produced image of an organism’s chromosomes that have been isolated from a cell and put in numerical order.

What are karyotypes used for?

Why is karyotyping important? Karyotypes are used to produce a karyotype analysis, which is used to identify chromosome abnormalities that are the cause of a disease or disorder. As karyotypes can be used to detect abnormalities in chromosomes, they can be used to identify blood disorders, lymphatic system disorders, some birth defects, and genetic diseases.

How are karyotypes prepared?

Karyotypes are prepared by researchers who take a picture of the chromosomes from a single cell, cut the chromosomes out, and arrange them by size, pattern, and position.

Which cells can be used to produce a karyotype?

When used to look for chromosomal abnormalities, researchers typically use karyotypes prepared from mitotic cells. Only dividing cells can be used for karyotyping. In the event that faster results are needed, fluorescent in situ hybridization, commonly called FISH, can be used. The most common cells for karyotyping are those in bone marrow or chorionic villus sampling, which collects tissue from a placenta. 

How are cells obtained to create a karyotype?

The cells needed to create a karyotype can be obtained in several ways, with the method used typically depending on the end goal that a researcher has in mind. For a cancer diagnosis, cells for a karyotype can be obtained through a tumor biopsy or a bone marrow sample. For diagnosis of a prenatal condition, cell samples can be taken from amniotic fluid or chorionic villus specimens. For most other cases, cell samples can come from a skin biopsy or peripheral blood samples. A sample can also be obtained from a cheek swab, which is also known as a buccal swab.