Karyotyping is a technique used to do chromosome analysis which helps to identify chromosomal abnormalities which are generally a cause of genetic diseases. To do chromosome analysis, the total number of chromosomes are counted and any structural changes in the chromosomes are observed. To perform this analysis, a sample of blood, bone marrow, amniotic fluid or placental tissue is used. To test amniotic fluid, an amniocentesis is performed. Testing on placental tissue is done after a chorionic villus sampling or after a miscarriage. A bone marrow specimen requires a bone marrow biopsy.

Chromosomes are the the storage bodies of the genes which are composed of the DNA. The collected cells/samples are induced to divide in the in vitro conditions and when they are in the metaphase stage, the cell division is arrested. In the metaphase stage the chromosomes are thick and easily visible under the light microscope as against the non-dividing cell where the chromatin looks like a tangled mesh with thin hairlike structures, which is difficult to observe. In the mitotic metaphase stage the chromosomes are stained with Giemsa dye which produces a banding pattern on the chromosomes. The Giemsa dye stains the regions of chromosomes that are rich in the base pairs adenine (A) and Thymine (T) and produce dark bands. The chromosomes are photographed to provide a karyotype which shows the arrangement of the chromosomes. The number and the arrangment can help to identify any abnormalities.

In human beings the females have 44 autosomes and 2 sex chromosomes (XX), denoted 46 (X,X) whereas males have 44 autosomes and 2 sex chromosomes (XY), denoted 46 (X,Y).If the total number of chromosomes vary from 46, then depending on which chromosome is missing or which one is extra, various genetic diseases associated with these is diagnosed. E.g Trisomy (Three copies of chromosme 21) of the chromosome no 21 indicates Down Syndrome, Trisomy 18, Philadelphia chromosome, Klinefelter syndrome, Turner syndrome, or other abnormalities. Sometimes a fetus is born with genitals that are neither well developed female or male, in such cases karyotyping helps to find out which chromosmes the baby has. Any issues regarding the confusion about baby’s gender can also be resolved e.g a baby may have penis and called a male may turn out to have the chromosmes (xx) of a female.


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