Chromosomal Genetic Testing

This test evaluates a person’s chromosomes, including their structure, number and arrangement. Parts of a chromosome can be missing, be extra or even be moved from its normal position to a different part of the same or of another chromosome.

What is karyotyping?

A common laboratory technique, Karyotyping is used widely to analyse chromosomes and evaluate any chromosomal anomaly which could be the cause of a genetic condition.

This test can count the number of chromosomes and look for structural changes in chromosomes. Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics.

How the test is performed?

The test can be performed on almost any tissue, including:

  • Blood
  • Amniotic fluid or chorionic villus (tissue from the placenta) during pregnancy to evaluate the chromosomes of the baby
  • Bone marrow

A chromosomal analysis may be ordered when:

  • a fetus is suspected of having a chromosomal abnormality
  • when an infant has congenital abnormalities
  • when woman experiences recurrent miscarriages or infertility
  • and when an adult shows signs of a genetic disorder.

It may also be ordered to detect the presence of chromosomal abnormality in family members when it has been detected in a child or in another family member.

How does karyotyping work?

A karyotype is a type of assessment technique, by which chromosomes within a single cell can be visualised and evaluated on the basis of the number of chromosomes, their arrangement, size and structure.

The chromosomes of a cell are stained with a dye and photographed using a microscope to produce a karyotype image.

A clinical scientist then analyses the image, where all the chromosomes are arranged in order of size, using specialised computer software.

It is preferred, that the karyotype analysis is done on cells at a stage when they are dividing. At this time the chromosomes are clearly visible under a microscope.

This is because, in the non-dividing stage the chromosomes exist as very long fine threads that are too thin to be seen. When a cell divides the fine threads are wound up into compact packages that can be easily seen and studied under the microscope.


Results of karyotype test are usually available within 2 weeks.

Normal Karyotype illustrates there are 46 chromosomes that can be grouped as 22 matching pairs and 1 pair of sex chromosomes (XX for a female and XY for a male). Also, the size, shape and structure are normal for each chromosome.

Abnormal karyotype demonstrates there are more than or fewer than 46 chromosomes. The size or shape of one or more chromosomes is abnormal and a chromosome pair may be broken or incorrectly separated. In case of an abnormal karyotyping, a pre implantation genetic diagnosis (PGD) is recommended.

Which conditions are tested for by karyotyping?

Karyotyping is used to look for chromosomal anomalies including trisomy presence of an extra chromosome, a third instead of a pair, for example Trisomy 21 the so called Down-Syndrome or Mongoloismus and translocations (pieces of chromosomes break off and re-attach to another chromosome. Karyotyping is one of the tests which is performed to evaluate the causes of recurrent miscarriage; severely impaired semen parameters; and significantly reduces ovarian reserve at a younger age.

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