Karyotyping - photographic representation of a stained preparation of chromosomes.
The photograph is itself called a “karyogram”/ Idiogram.
It is based on the fact that chromosomes have specific size, number, length, position etc.
Chromosomes can be studied in any nucleated cell.
Procedure:
Whole blood is collected.
Incubated in a media containing phytohaemoagglutinin - to stimulate mitosis
WBCs are arrested at metaphase by colchicine.
Spread on a slide.
Stained with Giemsa stain.
Samples that can be used:
Peripheral Blood, Amniotic Fluid, Chorionic Villus, Skin Biopsy, Tumor Biopsies, Bone Marrow etc.
Based on the staining techniques used, different banding patterns are produced and we have different Banding techniques.
G-banding: Giemsa stain - better resolution of individual bands, produces more stable preparation, & can be analyzed with ordinary bright-field microscopy.
Q-banding: Quinacrine fluorescence stain
R-banding: Reverse Giemsa staining
C-banding: Constitutive heterochromatin distribution - genetically inactive DNA; rarely used for diagnosis
Interpretation:
Classification of chromosomes based on location of centromere:
Centromere - constriction at which the chromatids are joined.
Telomere - Terminal end of a chromosome.
Chromosomal Disorders Detected by Karyotyping
The photograph is itself called a “karyogram”/ Idiogram.
It is based on the fact that chromosomes have specific size, number, length, position etc.
Chromosomes can be studied in any nucleated cell.
Procedure:
Whole blood is collected.
Incubated in a media containing phytohaemoagglutinin - to stimulate mitosis
WBCs are arrested at metaphase by colchicine.
Spread on a slide.
Stained with Giemsa stain.
Samples that can be used:
Peripheral Blood, Amniotic Fluid, Chorionic Villus, Skin Biopsy, Tumor Biopsies, Bone Marrow etc.
Based on the staining techniques used, different banding patterns are produced and we have different Banding techniques.
G-banding: Giemsa stain - better resolution of individual bands, produces more stable preparation, & can be analyzed with ordinary bright-field microscopy.
Q-banding: Quinacrine fluorescence stain
R-banding: Reverse Giemsa staining
C-banding: Constitutive heterochromatin distribution - genetically inactive DNA; rarely used for diagnosis
Interpretation:
Classification of chromosomes based on location of centromere:
Centromere - constriction at which the chromatids are joined.
Telomere - Terminal end of a chromosome.
- Centromeres in the middle of a chromosome (metacentric)
- Centromere closer to one end than the other (submetacentric)
- Centromere very close to one end (acrocentric)
- Chromosomes are arranged into seven groups based on size, centromere location and banding pattern.
- Human autosomes are numbered from 1 to 22, in descending order by size.
- Sex chromosomes are placed at end of a karyogram.
- Short p (petite) arms are at top & long q (queue) arms are at bottom.
- Chromosomes are aligned along a horizontal axis shared by their centromeres.
Chromosomal Disorders Detected by Karyotyping
- Aneuploidy: Often caused by absence or addition of a chromosome.
- Down syndrome (Trisomy 21) caused by an extra chromosome 21
- Edwards syndrome (Trisomy 18) caused by an extra chromosome 18
- Patau syndrome (Trisomy 13) caused by an extra chromosome 13
- Chromosomal Deletions (Cri du chat syndrome, Angelman syndrome, Prader-Willi syndrome)
- Insertions, Duplications, Translocations, or Inversions.
- Klinefelter syndrome caused by an extra X chromosome
- Turner syndrome caused by missing one X chromosome in females
- Certain haematologic and lymphoid disorders (e.g., Leukaemia, Lymphoma, Myeloma, Refractory Anaemia)
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