a Southern blot, and how each allele (two per individual) might be inherited in members of a family. In the third schematic, the probe and restriction enzyme are chosen to detect a region of the genome that includes a variable number tandem repeat (VNTR) segment (boxes in schematic diagram). In allele c, there are five repeats in the VNTR, and the probe detects a longer fragment between the two restriction sites. In allele d, there are only two repeats in the VNTR, so the probe detects a shorter fragment between the same two restriction sites. Other genetic processes, such as insertions, deletions, translocations, and inversions, can also lead to polymorphisms. RFLP tests require much larger samples of DNA than do short tandem repeat (STR) tests. Applications Analysis of RFLP variation in genomes was formerly a vital tool in genome mapping and genetic disease analysis. If researchers were trying to initially determine the chromosomal location of a particular disease gene, they would analyze the DNA of members of a family afflicted by the disease, and look for RFLP alleles that show a similar pattern of inheritance as that of the disease (see genetic linkage). Once a disease gene was localized, RFLP analysis of other families could reveal who was at risk for the disease, or who was likely to be a carrier of the mutant genes. RFLP test is used in identification and differentiation of organisms by analyzing unique patterns in genome. It is also used in identification of recombination rate in the loci between restriction sites. RFLP analysis was also the basis for early methods of genetic fingerprinting, useful in the identification of samples retrieved from crime scenes, in the determination of paternity, and in the characterization of genetic diversity or breeding patterns in animal populations. Alternatives The technique for RFLP analysis is, however, slow and cumbersome. It requires a large amount of sample DNA, and the combined process of probe labeling, DNA fragmentation, electrophoresis, blotting, hybridization, washing, and autoradiography can take up to a month to complete. A limited version of the RFLP method that used oligonucleotide probes was reported in 1985. The results of the Human Genome Project have largely replaced the need for RFLP mapping, and the identification of many single-nucleotide polymorphisms (SNPs) in that project (as well as the direct identification of many disease genes and mutations) has replaced the need for RFLP disease linkage analysis