Polymorphism
Definition
The existence of two or more sequence variants (alleles) at a locus in a population at a frequency above one percent. High polymorphism at a locus means that different individuals are likely to carry different alleles, which is what makes a locus useful for individualisation.
- Frequency threshold
- Above 1 percent in the population
- Forensic relevance
- Enables individualisation at a locus
- Contrast
- Distinct from a rare mutation
Common questions
How does polymorphism differ from mutation?+
A polymorphism is a variant common enough in the population to exceed the one percent threshold, while a mutation below that frequency is treated as a rare event rather than a routine population variant.
Why do forensic DNA panels target highly polymorphic loci?+
A locus with many common alleles gives a much higher chance that two unrelated people differ at it, which is what drives the discriminating power of a DNA profile.
Related terms
- Chromosome
- A discrete, condensed structure consisting of a single long DNA molecule complexed with histone proteins. Humans normally carry 46 chromosomes in 23...
- Gene
- A segment of DNA that encodes a functional product, most commonly a protein but also non-coding RNA molecules. Protein-coding genes occupy roughly...
- Heterozygosity
- The proportion of individuals in a population who carry two different alleles at a locus. A locus with high heterozygosity is more...
- Locus (Plural: Loci)
- A defined physical position on a chromosome. In forensic genetics, 'locus' usually refers to a specific STR site used in profiling. The...
- Short Tandem Repeat (STR)
- Short repetitive DNA sequences scattered throughout the genome, with the number of repeats varying between individuals at each locus. DNA profiling compares...