Molecular Basis of Inheritance
DNA Fingerprinting
DNA fingerprinting tells people apart by reading only the short, repeated stretches of DNA that vary a lot from one person to the next.
Almost all of your DNA is identical to everyone else's. A tiny part is not. In some places a short sequence repeats over and over, and the number of repeats differs from person to person. These are called VNTRs, Variable Number of Tandem Repeats.
DNA fingerprinting looks only at these variable spots. The DNA is cut, the fragments are sorted by size using electrophoresis, and a probe lights up the VNTR bands. The pattern of bands is what differs between people. Identical twins are the one exception: their patterns match.
Where students slip up
The common mistake is thinking DNA fingerprinting reads your whole genome. It does not. It checks only the highly variable repeat regions, because that is where people differ most. Reading the entire genome would be slow, costly, and pointless, since most of it is the same between any two people.
Hold onto this
It reads the repeats that vary, not the whole genome.
Why it helps in the exam: questions ask for the correct order of steps, what VNTR means, and the forensic or paternity use. Remember the sequence: cut, separate, blot, probe, read.
Where this connects
The same band pattern that clears or convicts a suspect also settles paternity, because these repeats are inherited like any other DNA, half from each parent. So a child's bands are just a mix of the mother's and the father's.
Why DNA carries this information →Quick check
DNA fingerprinting mainly analyses:
- AThe entire genome sequence
- BHighly variable repetitive DNA (VNTRs)
- COnly the protein-coding genes
- DMitochondrial DNA alone