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# DNA polymorphisms, linkage and DNA fingerprinting

Small DNA differences between people are inherited markers: they follow genes through families and can identify a person from a drop of blood.

Updated Nov 12, 2026

## Key facts

- A polymorphism is a DNA variant common in the population (more than 1%), usually harmless.
- SNP: a single-base difference, the most frequent kind (millions in each genome).
- Microsatellites (STRs) are short repeats of 2–6 bases whose number of copies varies between people; VNTRs (minisatellites) are longer repeats.
- RFLP: a variant that creates or removes a restriction-enzyme site, so the DNA is cut into fragments of different length.
- DNA fingerprinting (profiling) compares the STR pattern at many loci; the combination is practically unique except in identical twins.

## In detail

- Each person inherits one allele of each marker from each parent, so profiles are used to test paternity and identify remains.
- Linkage analysis: loci close together on a chromosome are inherited together more often than chance, because recombination rarely separates them; following a marker through a family tracks a nearby disease gene even before the gene is known.
- Genome-wide association studies compare SNPs in people with and without a disease to find regions linked to common, multifactorial disorders.
- The Human Genome Project (completed in 2003) produced a reference sequence of about 3 billion base pairs, with about 20 000 protein-coding genes.
- Microsatellite instability (changing STR lengths within a tumour) is a sign of defective mismatch repair.

**Also called**
RFLP, STR and SNP, DNA profiling

## Clinical notes

- Forensic medicine and paternity testing use STR panels; the weight of the evidence is the probability of a chance match.
- Testing colorectal and endometrial cancers for microsatellite instability screens for Lynch syndrome and helps choose immunotherapy.
- Before direct sequencing, RFLP linkage in a family with an affected child allowed prenatal diagnosis.

## Test yourself

Think of the answer, then tap the question to see it.

## What makes STR profiles useful for identifying a person?

The number of repeats at each locus varies between people; combining many loci gives a pattern that is practically unique.

## What is the basis of linkage analysis?

Loci close together on a chromosome are rarely separated by recombination, so a marker travels with a nearby disease gene in a family.

## What does microsatellite instability in a tumour suggest?

Defective DNA mismatch repair, as in Lynch syndrome.

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## Connections

## Related conditions 2

- [Lynch syndrome (hereditary non-polyposis colorectal cancer)](https://durgical.com/en/conditions/lynch-syndrome/)
- [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/)

## Related 6

- [Recombinant DNA and cloning](https://durgical.com/en/biochemistry/topics/recombinant-dna-and-cloning/)
- [Polymerase chain reaction (PCR)](https://durgical.com/en/biochemistry/topics/polymerase-chain-reaction/)
- [DNA sequencing](https://durgical.com/en/biochemistry/topics/dna-sequencing/)
- [Southern, Northern and Western blots](https://durgical.com/en/biochemistry/topics/southern-northern-and-western-blots/)
- [DNA repair](https://durgical.com/en/biochemistry/topics/dna-repair/)
- [Genetic tests: what each one finds](https://durgical.com/en/biochemistry/topics/genetic-tests-what-each-one-finds/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Microsatellite](https://www.genome.gov/genetics-glossary/Microsatellite) (National Human Genome Research Institute (NHGRI), 2026); [Restriction Fragment Length Polymorphism (RFLP)](https://www.genome.gov/genetics-glossary/Restriction-Fragment-Length-Polymorphism) (National Human Genome Research Institute (NHGRI), 2026); [DNA Fingerprinting](https://www.genome.gov/genetics-glossary/DNA-Fingerprinting) (National Human Genome Research Institute (NHGRI), 2026); [Linkage](https://www.genome.gov/genetics-glossary/Linkage) (National Human Genome Research Institute (NHGRI), 2026); [Human Genome Project](https://www.genome.gov/genetics-glossary/Human-Genome-Project) (National Human Genome Research Institute (NHGRI), 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/dna-polymorphisms-linkage-and-dna-fingerprinting/