08-18-2013, 05:36 AM
Karyotyping is a technique used for screening for genetic disorders. A karyotype refers to the number and size of chromosomes in the nucleus of an organism’s cell. The arrangement of chromosomes according to a pattern (usually number) is known as a karyogram or an ideogram.
Since it is very difficult to spot chromosomes under a light microscope, the chromosomes have to be stained in order to allow proper visualization of the condensation and also the banding patterns. Traditional stains cannot be used for staining chromosomes; instead stains like Giemsa and quinacrine are used.
Once the chromosomes have been visualized under the light microscope, the chromosomes are arranged according to their number. The arrangement formed is then compared to a standard to determine the presence or absence of any abnormality.
It is possible to perform karytoping of chromosomes collected from any nucleated cell; however for cytogenetic purposes lymphocytes, skin or tumour cells are preferably used in adults and amniotic cells or chorionic villi cells in foetuses. Knowledge of a genetic disorder at an early age makes treatment and management much easier.
Amniocentesis is a form of prenatal testing involving karyotyping. This test, also known as amniotic fluid testing is done to screen for any chromosomal aberrations in a fetus. Between 15th and 20th week of gestation, the physician after giving a local anaesthetic to the mother extracts 20 ml of amniotic fluid using a syringe. This fluid is then cultured for foetal cells which are analysed and a karyotype is performed.
Amniocentesis can indicate any chromosome disorder and also other developmental disorders like lung immaturity, Rh incompatibility etc. However, since this technique can be misused to detect the sex of the fetus and is therefore banned in some countries. Chorionic villi sampling or CVS is a technique similar to amniocentesis where cells from the chorionic villi are taken and analysed for chromosomal aberrations.
Most developed countries advice expecting parents to undergo amniocentesis and karyotyping for screening for a variety of diseases. Some of these are Down’s syndrome, Turner’s syndrome, Fragile X syndrome, Edward’s syndrome, HIV etc.
Since it is very difficult to spot chromosomes under a light microscope, the chromosomes have to be stained in order to allow proper visualization of the condensation and also the banding patterns. Traditional stains cannot be used for staining chromosomes; instead stains like Giemsa and quinacrine are used.
Once the chromosomes have been visualized under the light microscope, the chromosomes are arranged according to their number. The arrangement formed is then compared to a standard to determine the presence or absence of any abnormality.
It is possible to perform karytoping of chromosomes collected from any nucleated cell; however for cytogenetic purposes lymphocytes, skin or tumour cells are preferably used in adults and amniotic cells or chorionic villi cells in foetuses. Knowledge of a genetic disorder at an early age makes treatment and management much easier.
Amniocentesis is a form of prenatal testing involving karyotyping. This test, also known as amniotic fluid testing is done to screen for any chromosomal aberrations in a fetus. Between 15th and 20th week of gestation, the physician after giving a local anaesthetic to the mother extracts 20 ml of amniotic fluid using a syringe. This fluid is then cultured for foetal cells which are analysed and a karyotype is performed.
Amniocentesis can indicate any chromosome disorder and also other developmental disorders like lung immaturity, Rh incompatibility etc. However, since this technique can be misused to detect the sex of the fetus and is therefore banned in some countries. Chorionic villi sampling or CVS is a technique similar to amniocentesis where cells from the chorionic villi are taken and analysed for chromosomal aberrations.
Most developed countries advice expecting parents to undergo amniocentesis and karyotyping for screening for a variety of diseases. Some of these are Down’s syndrome, Turner’s syndrome, Fragile X syndrome, Edward’s syndrome, HIV etc.
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