A chromosome analysis, or karyotype, is the traditional testing that can been done on cells from chorionic villus sampling (CVS) and amniocentesis procedures, or from a blood sample. A karyotype involves the lab examining the cells and determining the number of chromosomes.
How the lab determines the number of chromosomes is a complicated process. Chromosomes all have bands on them, which kind of look like stripes. The pattern of the bands can help the lab determine which chromosome they’re looking at. For example, chromosome 21 has a very different banding pattern than chromosome 22.
These bands aren’t easily visible so the lab uses staining, much like you would stain a glass window, to show the pattern of bands on the chromosome. The lab can then use that pattern to figure out what number chromosome they are looking at. They then use a computer to put the chromosomes in order. Most people have two of each chromosome, so the lab would use the computer to move the chromosome number 1s together, and next the chromosome number 2s together, and so on.
Once all 23 sets of chromosomes are laid out we get a picture, which is the karyotype. This allows us to see if there are any extra (called a trisomy) or missing (called a monosomy) chromosomes. A karyotype can also identify if large pieces of chromosomes:
-
- Have broken off and turned upside down (called chromosome inversions),
-
- That are missing (called chromosome deletions), or
- That are extra (called chromosome duplications).
If there is a trisomy, monosomy, translocation, inversion, deletion, or duplication, it is important to determine what chromosome(s) are involved. Each chromosome has different information on it, so if there is extra or missing chromosome information, what is extra or missing can help us determine if it can cause health concerns.
Karyotype results are usually back within 2-3 weeks after the lab receives them. It is important to remember that a karyotype can be diagnostic for large chromosome differences, but cannot identify all genetic or hereditary conditions.
Related Articles
We have over 20,000 genes in our body, and each gene has a very specific job. To do that job, our genes make substances called proteins that make everything in the body work, grow, and function properly. A gene is made up of a long string of many letters (A,…
We have over 20,000 genes in our body, and each gene has a very specific job. To do that job, our genes make substances called proteins that make everything in the body work, grow, and function properly. A gene is made up of a long string of many letters that…
Next generation sequencing (aka panel testing) is a relatively newer technology that allows the lab to look at many different genes in a faster and more cost-effective way than ever before. This type of testing can be particularly helpful in situations where there are many potential explanations for what we…
Genetic testing for someone who may be at risk for an inherited disease is always easier if we know the specific genetic cause. Often times, the best way to find the genetic cause is to start by testing someone in the family who is known or strongly suspected to have…
A chromosomal microarray (CMA) is a test that can be done to look for specific kinds of chromosome changes called microdeletions and microduplications. Much like a traditional chromosome analysis, CMA generally looks at all 23 pairs of chromosomes. While the chromosome analysis is looking for large changes (extra or missing…
With genetic testing, there are generally three different results that we can get: a positive, a negative, or a variant of uncertain significance (VUS). Positive A positive result means that a harmful change (called a pathogenic variant) was found in a gene that causes that gene to not work properly.…
Whether or not to pursue any genetic testing is a very personal decision. In some cases, moving forward with genetic testing may help to provide an answer to a health question that is running in someone's family, or may help to provide a name to a medical condition that someone…
Last updated on Feb 12th, 2019
