Locus (Plural: Loci)
Definition
A defined physical position on a chromosome. In forensic genetics, 'locus' usually refers to a specific STR site used in profiling. The different sequence variants found at a locus across a population are called alleles.
- Definition
- A defined physical position on a chromosome
- Forensic use
- Specific STR site used in DNA profiling
- Related term
- Allele: a sequence variant found at a locus
- Plural form
- Loci
Common questions
How does a locus differ from an allele in forensic genetics?+
A locus is the fixed physical position on the chromosome being examined, while an allele is the particular sequence variant found at that position in a given individual.
Why do forensic STR profiles examine multiple loci rather than just one?+
Combining results across several independent loci multiplies the discriminating power of a match, drastically reducing the chance that two unrelated individuals would match by coincidence.
Related terms
- Chromosome
- A chromosome is an organised DNA-containing structure that carries genetic information. Human nuclear chromosomes contain DNA packaged with proteins. Most human body...
- 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
- Heterozygosity describes genetic variation at a locus. Observed heterozygosity is the proportion of sampled individuals with two different alleles. Expected heterozygosity is...
- Polymorphism
- The existence of two or more sequence variants (alleles) at a locus in a population at a frequency above one percent. High...
- 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...