Heterozygosity
Definition
The proportion of individuals in a population who carry two different alleles at a locus. A locus with high heterozygosity is more informative for forensic profiling than one where most people carry the same allele. CODIS loci were selected partly for their high heterozygosity values.
- Definition scope
- Population-level, proportion carrying two different alleles
- Forensic significance
- Higher heterozygosity means more discriminating power
- CODIS relevance
- Loci selected partly for high heterozygosity
- Field
- Forensic DNA profiling and population genetics
Common questions
Why does a highly heterozygous locus matter more for identification?+
A locus where most people share the same two alleles produces the same genetic profile across much of the population, so it contributes little to distinguishing individuals. A locus with many different alleles spread across the population produces far more unique combinations and drives down the random match probability.
Does heterozygosity vary between different population groups?+
Yes. Allele frequencies at a given locus differ across population groups, so the observed heterozygosity and the resulting match statistics are calculated against population-specific reference databases rather than a single universal figure.
Related terms
- Amelogenin
- A gene on both the X and Y chromosomes used for sex determination in forensic STR kits. The X-allele amplicon is approximately...
- Chromosome
- A discrete, condensed structure consisting of a single long DNA molecule complexed with histone proteins. Humans normally carry 46 chromosomes in 23...
- CODIS
- The FBI's Combined DNA Index System, the US national STR-based forensic DNA database. Contains profiles from convicted offenders, arrestees, and unidentified crime-scene...
- ESS (European Standard Set)
- The set of STR loci required for profiles entered into EU national databases participating in Prüm cross-border DNA exchange. Currently aligned with...
- 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...
- 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...
- 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...
- STR (Short Tandem Repeat)
- A genomic locus where a 2, 7 base-pair unit is repeated in tandem a variable number of times between individuals. The variation...
- VNTR (Variable Number Tandem Repeat)
- A tandemly repeated genomic sequence with a longer repeat unit (typically 10, 60 bp) than an STR. VNTRs were used in the...
Explained in these topics
- Chromosomes, Genes and the Human Genome
- Polymorphism, Heredity and the Markers that Identify a PersonThe probability that two alleles chosen at random from a population at a given locus are different. A locus with heterozygosity approaching 1.0 is maximally in...