Table of ContentsView AllTable of ContentsGenetics BasicsWhat a Karyotype Can ShowIndicationsHow They’re PerformedResults
Table of ContentsView All
View All
Table of Contents
Genetics Basics
What a Karyotype Can Show
Indications
How They’re Performed
Results
DEPT. OF CLINICAL CYTOGENETICS, ADDENBROOKES HOSPITAL / Science Photo Library / Getty Images
Chromosomes are the thread-like structures in the nucleus of cells that we inherit from our parents and that carry our genetic information in the form ofgenes. Genes direct the synthesis of proteins in our bodies, which determines how we look and function.
All humans typically have 46 chromosomes, 23 of which we inherit from our mothers and fathers, respectively. The first 22 pairs are calledautosomes, which determine our unique biological and physiological features. The 23rd pair is composed of sex chromosomes (known as X or Y), which designate whether we are female or male.
Any error in genetic coding may affect development and the way our bodies work. In some cases, it can place us at an increased risk of a disease or a physical or intellectual defect. A karyotype allows healthcare providers to detect these errors.
Chromosomal defects occur when a cell divides during fetal development. Any division occurring in the reproductive organs is called meiosis. Any division occurring outside of the reproductive organs is called mitosis.
A karyotype characterizes chromosomes based on their size, shape, and number to identify both numerical and structural defects. While numerical abnormalities are those in which you either have too few or too many chromosomes, structural abnormalities can encompass a wide range of chromosomal flaws, including:
Numerical Abnormalities
Some people are born with either an extra or missing chromosome. If there are more than two chromosomes where there should only be two, this is called a trisomy. If there is a missing or damaged chromosome, that is a monosomy.
Among some of the numerical abnormalities a karyotype can detect are:
Structural Abnormalities
Structural abnormalities are not as commonly seen or identified as trisomies or monosomies, but they can be every bit as serious.Examples include;
During pregnancy, a karyotype test may be done to help detect genetic conditions in the fetus.Karyotypes are sometimes used for preconception screening under specific conditions, namely:
Karyotyping is not used for routine preconception screening but rather for couples whose risk is considered high. Examples include Ashkanzi Jewish couples who are at high risk ofTay-Sachs diseaseor African American couples with a family history of sickle cell disease.
Couples who are either unable to conceive or experience recurrent miscarriage may also undergo parental karyotyping if all other causes have been explored and excluded.
Finally, a karyotype may be used to confirm chronic myeloid leukemia in association with other tests. (The presence of the Philadelphia chromosome on its own cannot confirm the cancer diagnosis.)
A karyotype can theoretically be performed on any body fluid or tissue, but, in clinical practice, samples are obtained in four ways:
Sample Evaluation
The cells are then placed on a slide, stained with a fluorescent dye, and positioned under the lens of an electron microscope. The cytogeneticist then takes microphotographs of the chromosomes and re-arranges the images like a jigsaw puzzle to correctly match the 22 pairs of autosomal chromosomes and two pairs of sex chromosomes.
Once the images are correctly positioned, they are evaluated to determine whether any chromosomes are missing or added. The staining can also help reveal structural abnormalities, either because the banding patterns on the chromosomes are mismatched or missing, or because the length of a chromosomal “arm” is longer or shorter than another.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American College of Obstetricians and Gynecologists.Prenatal Genetic Diagnostic Tests.Leukemia & Lymphoma Society.Blood and Bone Marrow Tests.National Human Genome Research Institute.Chromosome Abnormalities Fact Sheet.Centers for Disease Control and Prevention.Facts about Down Syndrome.National Library of Medicine.Karyotype genetic test.Thompson PA, Kantarjian HM, Cortes JE.Diagnosis and Treatment of Chronic Myeloid Leukemia in 2015.Mayo Clin Proc. 2015;90(10):1440–1454. doi:10.1016/j.mayocp.2015.08.010American College of Obstetricians and Gynecologists.Amniocentesis.American College of Obstetricians and Gynecologists.Prenatal genetic diagnostic tests.
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American College of Obstetricians and Gynecologists.Prenatal Genetic Diagnostic Tests.Leukemia & Lymphoma Society.Blood and Bone Marrow Tests.National Human Genome Research Institute.Chromosome Abnormalities Fact Sheet.Centers for Disease Control and Prevention.Facts about Down Syndrome.National Library of Medicine.Karyotype genetic test.Thompson PA, Kantarjian HM, Cortes JE.Diagnosis and Treatment of Chronic Myeloid Leukemia in 2015.Mayo Clin Proc. 2015;90(10):1440–1454. doi:10.1016/j.mayocp.2015.08.010American College of Obstetricians and Gynecologists.Amniocentesis.American College of Obstetricians and Gynecologists.Prenatal genetic diagnostic tests.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American College of Obstetricians and Gynecologists.Prenatal Genetic Diagnostic Tests.Leukemia & Lymphoma Society.Blood and Bone Marrow Tests.National Human Genome Research Institute.Chromosome Abnormalities Fact Sheet.Centers for Disease Control and Prevention.Facts about Down Syndrome.National Library of Medicine.Karyotype genetic test.Thompson PA, Kantarjian HM, Cortes JE.Diagnosis and Treatment of Chronic Myeloid Leukemia in 2015.Mayo Clin Proc. 2015;90(10):1440–1454. doi:10.1016/j.mayocp.2015.08.010American College of Obstetricians and Gynecologists.Amniocentesis.American College of Obstetricians and Gynecologists.Prenatal genetic diagnostic tests.
American College of Obstetricians and Gynecologists.Prenatal Genetic Diagnostic Tests.
Leukemia & Lymphoma Society.Blood and Bone Marrow Tests.
National Human Genome Research Institute.Chromosome Abnormalities Fact Sheet.
Centers for Disease Control and Prevention.Facts about Down Syndrome.
National Library of Medicine.Karyotype genetic test.
Thompson PA, Kantarjian HM, Cortes JE.Diagnosis and Treatment of Chronic Myeloid Leukemia in 2015.Mayo Clin Proc. 2015;90(10):1440–1454. doi:10.1016/j.mayocp.2015.08.010
American College of Obstetricians and Gynecologists.Amniocentesis.
American College of Obstetricians and Gynecologists.Prenatal genetic diagnostic tests.
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