Back to monitoring outcomes


  • Biodiversity

  • Structure


Heterozygosity is a measure of genetic variation within a population and refers to individuals that carry two different alleles at a given locus (Leroy et al. 2018). Loss of heterozygosity is a driver of genetic erosion and is linked to genetic drift and inbreeding (Leroy et al. 2018, Gaggiotti et al. 2018). There is a direct relationship between heterozygosity and Effective population size (Wang et al. 2016). Reduced heterozygosity (i.e. genetic variation) can lead to reduced fitness and loss of adaptive potential (Leroy et al. 2018).

Methodology summary

As with calculation of Effective population size and Allelic diversity, estimation requires the collection and analysis of genetic data that requires a high level of technical expertise.

Calculation of heterozygosity requires a high marker density (markers across multiple loci, to give an overall assessment of heterozygosity within an individual’s genome) but can be assessed with a low sample size (<100 individuals within a population sampled e.g. DNA extracted from blood or animal/plant tissue) (Leroy et al. 2018).

Metrics include:

  • Runs of homozygosity (F metric) – provide information on the history of inbreeding in a population
  • Change in heterozygosity (He) – rate of loss of heterozygosity is a measure of genetic drift
  • Effective number of alleles (Ae) – probability that two randomly chosen genes in a population are identical by descent (reflects the expected frequency of homozygous individuals in a population)

Metric threshold or direction of change

The desired heterozygosity will be species/project specific. Generally, a higher level of heterozygosity is better.


  • Agricultural
  • Forest
  • Grassland
  • Heathland
  • Other
  • Peatland
  • Saltmarsh
  • Wetland


  • Landscape


  • High


  • Future

Technical expertise

  • High

Standardised methodology

  • No