karyotype, clinical

What is a karyotype?

A karyotype is a visual representation of all the chromosomes in a cell, organized and displayed in a standardized format.

Steps in Karyotyping

1. Cell Collection: Obtain a sample of cells (e.g., blood, skin, amniotic fluid).
2. Cell Culture: Grow the cells in a laboratory to increase their number.
3. Metaphase Arrest: Treat cells with chemicals (e.g., colchicine) to halt mitosis at metaphase when chromosomes are most condensed and visible.
4. Slide Preparation: Swell cells (hypotonic solution) and fix them on a slide.
5. Chromosome Staining: Stain chromosomes with dyes (e.g., Giemsa) to create banding patterns.
6. Microscopy: Observe chromosomes under a microscope.
7. Karyotype Construction: Arrange chromosomes in pairs based on size, banding patterns, and centromere position.

Giemsa Staining

Giemsa staining is a common technique that produces characteristic banding patterns on chromosomes, aiding in their identification. The bands are regions of DNA with varying composition and condensation levels.

Applications of Karyotyping

Karyotyping is used to detect chromosomal abnormalities, diagnose genetic disorders, determine the sex of an individual, and study evolutionary relationships.

What is the difference between a karyogram and karyotype?

Karyogram: Image of ordered chromosomes
Karyotype: Alpha-numeric description of the karyogram

What are direct vs. indirect methods of karyotyping?

Direct: No culture needed; e.g., bone marrow, tumors
Indirect: Requires in vitro culture; e.g., lymphocytes, amniocytes

Steps of the indirect method for lymphocyte karyotyping?

1. Blood in heparin tube
2. Culture with PHA and fetal serum
3. Colchicine to arrest metaphase
4. KCl hypotonic treatment
5. Fixation (methanol:acetic acid)
6. Microscopy + staining

Indications for karyotype testing?

Congenital anomalies in children
Mental retardation (e.g., Fragile X)
Reproductive issues
Ambiguous genitalia
Pubertal disorders
Hematologic malignancies (e.g. Philadelphia chromosome t(9;22))
Chromosomal instability syndromes (e.g., Fanconi anemia)
Occupational/radiation exposure
Prenatal suspicion of genetic disease