Postnatal Tests

*What is a karyotype?

A karyotype is simply a picture of an individual's chromosomes. In this technique, the status of an individual's chromosomes and possible numerical or structural changes are determined. Chromosomal abnormalities are a major cause of infertility and birth defects. Therefore, karyotype has a special place in investigating the causes of infertility. Karyotype is the arrangement of chromosomes together and comparing them to a healthy sample to identify possible defects. Many genetic diseases are caused by abnormalities in the state of chromosomes. Therefore, increasing or decreasing the number of chromosomes or their displacements will cause disease. Determining the status of chromosomes and examining their numerical or structural changes is possible by performing karyotyping. This test can be done on blood samples, bone marrow, and tissue or fetal samples. To perform a karyotype test, blood cells, bone marrow, or embryonic tissues are first proliferated in an environment rich in nutrients and vitamins necessary in the presence of stimulants of cell growth. The cells then stop at a stage in the cell cycle where the chromosomes are detectable. In the next step, the chromosomes are stained and carefully examined under a microscope. The discrimination of this experiment is limited to the resolution of a light microscope. With this degree of resolution, many chromosomal changes are detectable. But many chromosomal deletions or duplications are also not detected.

 *Fluorescence in situ hybridization (FISH) technique

This technique has been widely used in clinical diagnoses since the mid-1990s. The basis of the FISH technique is the ability of a fragment of a single-stranded DNA molecule to bind to its complementary sequence on a metaphase chromosome, an interphase nucleus, or an extended chromatin fiber. So, there will be a need for special processing stages. This molecule is called a probe and is a small piece of DNA labeled with fluorescent tags. Fluorochromes allow the hybridization region to be detected using fluorescent microscopes. Prenatal diagnosis of chromosomal abnormalities using in situ fluorescent hybridization (FISH) has many applications. In this technique, since the probe molecules hybridize directly with the intracellular DNA and RNA molecules, the binding position of the DNA fragment to the chromosome can be easily determined under a microscope. In fact, this technique is the result of combining cytogenetics with molecular genetic technologies. This method can be used to detect common aneuploidies on chromosomes 13, 18, 21, X and Y. It is also used to detect unbalanced chromosomes resulting from deletions or displacements identified in a previous child or parent. The FISH method also has a special place in confirming mosaic states, as it allows the counting of large numbers of cells.

*Chromosomal Abnormalities