Karyotyping

The Karyotype is the image of the chromosomes of an individual. Cytogeneticists prepare a complete set of metaphase chromosomes from each cell of an individual organism. Different types of specimens can be used like peripheral blood, CVS, amniotic fluid, bone marrow aspirations, and tissue. Cytogenticist takes a photograph of metaphase chromosome from a cultured specimen of an individual and arranges the chromosomes according to their size, centromeric position, and banding pattern. Karyotype describes the number of chromosomes and any structural abnormality. Humans contain 23 pairs of chromosomes.

How does it work?

Chromosomes were first discovered by Swiss botanist Karl Nageli in pollen in the year 1842. Since its discovery, different scientists used improved methods to prepare metaphase chromosomes and different staining techniques to study 23 pairs of human chromosomes. In 1956 Joe HinTijo and Albert Levan developed an improved methodology to arrest the cells at metaphase using colchicine and used hypotonic solution to prepare better chromosome spread. In 1970, scientists developed different banding techniques like C, Q, and G to reveal complex structural abnormalities.

The bands on individual chromosomes are specific and are representations for euchromatin (light band)and heterochromatin (dark band)regions.The euchromatin region is less condensed and transcriptionally active where as heterochromatin is highly condensed and transcriptionally inactive.The regions have been identified using a variety of banding techniques and are numbered according to the landmark system adopted at the Paris Conference (1971). The landmarks and band numbers have been selected to make comparisons with the human karyotype simpler, and chromosomes have been arranged homologies with the specific human chromosomes. The International System for Human Cytogenetic Nomenclature is the standard tool to describe the human chromosomes and chromosomal aberrations (ISCN) which was established in 1978. Based on the location of centromere (Meta , sub meta & acrocentric)and the size, Human chromosomes can be classified into 7 groups from A to G. A-group consists 1,2 &3 ;B –group consists 4& 5 ; C-group consists 6 to 12 & X ; D-group consists 13-15; E-group consists 16-18; F-group consists 19 & 20; G-group consists 21, 22 & Y chromosomes respectively.

Is it right for me?

During certain weeks of your pregnancy, your doctor will suggest which karyotype test is right for you based on how far along you are in your pregnancy and on your risks.

It’s more likely your baby could have a chromosome problem if:

– You’re 35 or older.

– You have another child or a family member who has a chromosome disorder.

– You or your partner has something unusual in your chromosomes.

– You have a history of miscarriages or had a baby that was stillborn.

Parental karyotype is suggested if the fetus with chromosomal abnormality, miscarriage with suspected chromosomal abnormality, multiple miscarriages or neonatal deaths is identified. It is done on venous blood collected from both the parents.