How are fragments of DNA different from each other?

Question

this is about DNA fingerprinting when they cut up a sample of DNA and separate out the fragments, how are they different from each other?

Answer 1

yes size is correct

Answer 2

size i think

Answer 3

They are all different. No two are alike.

Answer 4

The DNA is digested with a known enzyme that cuts reliably at certain sites along the DNA. This reduces the DNA to fragments, but it is not random. This digestion produces a pattern of shorter lengths. The fingerprint is contained in the exact pattern produced by the specific digestion of the DNA.

Comparing people genetically involves digesting the DNA and comparing the patterns the digestions create. DNA will contain the same genes in the same order but with different alleles present for each gene so the exact sequences vary slightly. Even the DNA regulating segments, which control gene expression, can vary in sequence so they will digest into different patterns. The digesting enzymes are very specific to the base pair sequences so if different alleles or regulating sequences are present there will be a different pattern between two people using the same digestion enzyme.

Answer 5

If you are separating DNA fragments of any type in some type of gel matrix, then with a few exceptions you are separating them by size - small fragments migrate faster than larger ones.

In DNA fingerprinting (or profiling as it is called these days) they no longer use DNA that has been cut into fragments. Loci called microsatellites or STR loci are amplified directly from genomic DNA using PCR.

These loci consist of blocks of repeated DNA e.g. a dinucleotide microsatellite might consist of the motif GAGAGAGAGA etc.

Alleles of this type of locus vary in the number of repeats they contain and so differ in size - hence you can separate the alleles on a polyacryalmide gel which can resolve fragment lengths down to a single base pair.