Blotting Procedures Function probe for specific substance in solution Southern blot - used to analyze DNA normally used to examine the presence of a particular DNA sequence remember: Southern Dixieland Northern blot - used to analyze RNA normally used to examine gene expression Western blot (immunoblot) - used to analyze protein Process run a gel electrophoresis to separate the components of the solution bands are transferred ("blotted") to a filter/membrane radiolabeled or fluorescently labeled probe is incubated with the membrane Southern blot - 32P-DNA Northern blot - 32P-DNA Western blot - enzyme-linked or 131I antibody specific probe binds with high specificity to DNA/RNA segment or protein of interest membrane is visualized under conditions to illuminate the probe Clinical use restriction length polymorphism (RFLP) can be used for genetic testing based on the principle that individuals have unique/heritable variations in RFLPs loss or gain of a restriction site changes the fragment lengths after digestion by an endonuclease variation provided in part by variable number tandem repeats (VNTRs) Southern blot used to visualize results ex.) testing for sickle-cell anemia wild type (wt) gene contains a restriction site in the gene fragment sickle cell (sc) gene lacks this restriction site the diagnostic results following a Southern blot wt homozygote would have only medium and small fragments heterozygote would have large, medium and small fragments sc homozygote would have only large fragments gene expression profiling measure whether a particular region of DNA is being expressed Northern blot used to visualize results ex.) testing for fragile X syndrome ↓ expression of FMR1 gene trinucleotide repeat disorder