Genetic Fingerprinting and Electrophoresis

Some genome regions contain variable numbers of tandem repeats, VNTRs. Different repeat counts can produce fragments of different lengths. Comparing several informative loci gives a much more discriminating profile than comparing one short region alone.

A typical diploid individual can have two alleles at a locus, inherited from the two parents. The profile concerns selected regions rather than every base in the genome. Identical twins and close relatives illustrate why relatedness and marker choice matter when interpreting a match.

PCR can amplify the selected regions before analysis. In gel electrophoresis, DNA’s negative charge causes movement towards the positive electrode under an electric field. For comparable fragments under the same conditions, smaller fragments generally travel farther through the gel.

A size ladder and consistent run conditions allow fragment lengths to be estimated. A band position corresponds to migration, not directly to the amount of a person’s total genome. Detection depends on the method used; the absence of a clear band could reflect sample quality or assay failure rather than a genuine absence of every allele.

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In a simple inheritance comparison, each child allele should be explainable by inheritance from one parent at a locus, subject to mutation and assay limitations. An incompatible pattern can provide exclusion evidence. A compatible profile supports a relationship but does not prove it with absolute certainty using only a small panel.

Forensic, breeding, conservation and medical contexts may use DNA patterns for different aims. Consider sample contamination, mixed samples, marker independence, relatives and the size of the comparison population. A small random-match probability is not identical to the probability that a particular accusation or biological explanation is true; contextual evidence still matters.

Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.