What Is Karyotype?

A karyotype can diagnose any chromosomal problems you may have

Male Karyotype. Credit: Media for Medical / Contributor / Getty Images

A karyotype is a picture of all of the chromosomes present in a single one of your cells. A karyotype is a test used to check for chromosomal abnormalities.

What a Karyotype Tells You

A karyotype can tell how many chromosomes a person has, as well as detect any errors those chromosomes may have. Normally, a person has 46 chromosomes or 23 pairs. Based on your karyotype, cytogeneticists (people who study chromosomes) can also determine your gender.

Two X chromosomes mean the person is female while an X and a Y chromosome means the person is male.

A karyotype can also diagnose any condition that results from extra or missing chromosomes. In addition to Down syndrome (trisomy 21), a karyotype can determine if you have:

  • Edward syndrome (trisomy 18)
  • Patau syndrome (trisomy 13)
  • Turner syndrome (one X)
  • Klinefelter syndrome (XXY)
  • XYY syndrome
  • Triple X syndrome (XXX)

Karyotypes can also determine the state of individual chromosomes and whether or not they have any deletions — like Cri-du-Chat syndrome (chromosome 5) or Williams syndrome (chromosome 7) — or translocations. Karyotypes can detect both reciprocal and Robertsonian translocations. About 2 to 3 percent of Down syndrome cases are caused by a translocation on chromosome 21. Robertsonian translocations can also cause Patau syndrome, Angelman syndrome, and Prader-Willi syndrome.

If you, or your child, has Down syndrome or any other trisomic condition.

Karyotypes taken from an assortment of different cells can determine whether or not you have a mosaic trisomy. Mosaicism means the trisomy is present in some cells and not others.

How a Karyotype Is Done

If your doctor has ordered a karyotype for you or your unborn child, your part of the process is fairly simple.

All you need to do is give a sample. If you are giving the sample, your sample will most likely be gathered from blood that was drawn during a doctor’s appointment, hospital, or a trip to a testing laboratory. If you are pregnant, a karyotype for your child will be done from either a sample of amniotic fluid or chorionic villi. Amniocentesis and chorionic villus sampling procedures are a bit more invasive than a blood test — both require a needle to be inserted into your abdomen — however, they are relatively painless procedures.

After your sample is collected, it will be analyzed by a special cytogenetics laboratory. The cytogenetic specialist analyzing your sample will separate your cells, grow them so that they have enough to analyze, and then release the chromosomes from the cells. Once the chromosomes are released, they are stained, analyzed, counted (to see if you have more or less than the normal 46 chromosomes), and sorted. The cytogeneticist will also look at the structure of the chromosome to make sure there is no missing or added genetic material.

Once this process is complete, the findings are written up for your doctor to share with you.

For karyotypes done on blood samples, results should be available within three to seven days. The results of karyotypes on prenatal samples take a bit longer — anywhere from 10 to 14 days.

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