what is it about short tandem repeat dna that makes it useful for dna fingerprinting
STR analysis STR analysis is a tool in forensic analysis that evaluates specific STR regions found on nuclear DNA. The variable (polymorphic) nature of the STR regions that are analyzed for forensic testing intensifies the discrimination between one DNA profile and another.[1] Forensic science takes advantage of the population's variability in STR lengths, enabling scientists to distinguish one DNA sample from another. The system of DNA profiling used today is based on PCR and uses simple sequences[2] or short tandem repeats (STR). This method uses highly polymorphic regions that have short repeated sequences of DNA (the most common is 4 bases repeated, but there are other lengths in use, including 3 and 5 bases). Because unrelated people almost certainly have different numbers of repeat units, STRs can be used to discriminate between unrelated individuals. These STR loci (locations on a chromosome) are targeted with sequence-specific primers and amplified using PCR. The DNA fragments that result are then separated and detected using electrophoresis. There are two common methods of separation and detection, capillary electrophoresis (CE) and gel electrophoresis.
S phase The major event in S-phase is DNA replication. The goal of this process is to create exactly two identical semi-conserved chromosomes. The cell prevents more than one replication from occurring by loading pre-replication complexes onto the DNA at replication origins during G1 phase which are dismantled in S-phase as replication begins. In synthesis, the enzyme helicase unwinds the DNA double helix, and the enzyme DNA polymerase re-binds free-floating nucleotides to the separate DNA single strands in accordance with the complementary base pairing rule. DNA synthesis can occur as fast as 2000 nucleotides/second [3] and must create fewer than 2 errors (I.e., wrong bases) in 1010 nucleotide additions.[citation needed]