ROH Profiles - Determination and Applications

ROH profiling involves genotyping the samples using SNP (single nucleotide polymorphism) arrays or by sequencing the entire genome. Special computational models identify the ROH and classify them according to their location and size. 

The unit of length is 1 Mb = 1,000,000 bases (base = single nucleotide of DNA). Depending on the objective and available initial data, the ROH are categorised into size ranges. In general, long ROH (> 10 Mb) are signs of recent inbreeding events and very short ROH (< 1 Mb) play are regarded as a population background with no role in the assessment of inbreeding. 

The information that can be provided with the help of ROH profiles are as follows:

For the individual animal that has been analysed:

1. The individual genomic inbreeding coefficient (GIK): This results from the entirety of the ROH, see article
2. Length of the ROH: The expansion of the ROHs is an indicator of the time at which the inbreeding mating(s) took place. 

At population level:

1. Genetic diversity: Analysing ROH patterns of animals in a population helps to estimate its genetic diversity. Diverse patterns indicate broad genetic variability, which can have a positive effect on the overall health of the population.
2. Detection of selection signals: ROH analyses can help to identify genomic regions that have been subject to selection, as these contain certain alleles that may be fixed in a population due to selection pressure.
3. Associations with health and disease: Certain ROH regions can correlate with genetic disorders and thus provide information about the health of individuals and populations.

The knowledge gained from the ROH profiles makes it possible for the first time to utilise inbreeding information that has been collected directly from the animal in question.

• Assessment of the overall extent of inbreeding in the animal being analysed, regardless of knowledge of the ancestors.
• Identification of offspring from incest mating.
• Control of inbreeding: Monitoring the ROH allows breeders to effectively control the level of inbreeding. This is crucial for maintaining the vitality and health of breeding populations.
• Utilisation in mating strategies to avoid crosses between closely related individuals.
• Selection for desirable traits: By linking specific ROH regions to traits of interest (e.g. disease resistance, growth rates), breeders can implement marker-assisted selection strategies.
• Improving the resilience of populations: Understanding the genetic structure of populations through ROH profiling allows breeders/breeding clubs to develop more resilient breeding stocks that can better withstand environmental changes and disease pressure.

The determination and calculation of Runs of Homozygosity (ROH) provides important insights into genetic diversity, inbreeding and population health. The integration of ROH analyses into breeding strategies will play a decisive role in modern genetics and animal husbandry in the future.

The determination of an animal's ROH profile is part of the ‘Inbreeding & Fitness’ test.

The examination can be ordered for dogs, horses and camelids (dromedaries, bactrian camels, alpacas)

Associated lexicon articles:

• genomic Heterozygosity (HE)
• genomic Inbreeding Coefficient (GIC, g-COI)

Literatur

1. Grilz-Seger, G., Druml, T., Neuditschko, M. et al. High-resolution population structure and runs of homozygosity reveal the genetic architecture of complex traits in the Lipizzan horse. BMC Genomics 20, 174 (2019). https://doi.org/10.1186/s12864-019-5564-x