1. Sample Collection:
* Blood: The most common source, as white blood cells (lymphocytes) are easily cultured.
* Amniotic fluid: Used in prenatal testing for chromosomal abnormalities.
* Chorionic villi: Another prenatal source, obtained from the placenta.
2. Cell Culture:
* The collected cells are grown in a lab environment to increase their number. This allows for enough cells to be analyzed.
3. Cell Synchronization:
* Cells are treated with chemicals that synchronize their cell cycle, ensuring that all chromosomes are at the same stage (metaphase), where they are most condensed and visible.
4. Harvesting and Staining:
* Cells are harvested and treated to break open the cell membranes and release the chromosomes.
* Chromosomes are stained with special dyes that bind to specific regions, creating banding patterns unique to each chromosome. This allows for identification of individual chromosomes.
5. Metaphase Spread Preparation:
* The stained chromosomes are carefully arranged on a microscope slide, ensuring they are spread out and not overlapping.
6. Microscopic Analysis:
* The slides are viewed under a microscope, and images of the chromosomes are captured.
7. Karyotype Construction:
* The images are arranged by size and banding patterns, resulting in a karyotype.
* Chromosomes are paired based on size and banding patterns, giving you a full set of 23 pairs (46 total) for a human.
* The karyotype is typically displayed in order from largest to smallest chromosome.
Analyzing the Karyotype:
* Biologists analyze the karyotype to:
* Identify chromosomal abnormalities like missing, extra, or rearranged chromosomes (e.g., Down Syndrome, Turner Syndrome).
* Determine the sex of the individual (XX for female, XY for male).
* Study the inheritance of genetic traits.
Important Note: This process takes time, often several days to a week, depending on the specific method used.
