DNA extraction

DNA Extraction from Paraffin-Embedded Tissues
Part one:
1- The most important factor affecting DNA quality is the type of fixative employed and the duration of fixation. Tissues fixed between 12 and 24 h in ethanol, acetone, Omnifix, or 10% buffered formalin usually yield good-quality DNA; but B-5, Zenker’s, or Bouin’s solutions, or duration of fixation longer than 5 d, are poor prognostic factors for PCR productivity.
2- Prior studies showed that when the length of ?-globin amplification product increased (175, 324, and 676 bp), the percentage of fixed tissues containing amplifiable DNA decreased (100, 69, and 45%). And when the age of a block increased, PCR productivity decreased, although some blocks stored for more than 40 yr were successfully studied .
3- Use a microtome to cut five sections, 5–20 µm thick, from a paraffin block.
4- Place these directly into a 1.5-mL microfuge tube.
5- The thickness of the sections depends on the size of the biopsy.
6- For a small biopsy (up to 3 mm), 20-µm thick sections may be required.
7- A large biopsy requires only 5-µm thick sections.
8- Although multiple thin sections can be placed in a single tube.
9- Fewer thick sections are more practical for processing.
10- Add 800 µL of xylene to each tube, close, mix by gentle vortexing, and then incubate at room temperature for 10 min.