Runs of homozygosity are unevenly located across the genome in highly inbred cattle

GIOVAMBATTISTA G.; MOLINA A.; DEMYDA PEYRÁS S.; GOSZCZYNSKI D.E.; MORALES DURAND H.F.

Dublin

Congreso; 36th International Society for Animal Genetics Conference; 2017

International Society for Animal Genetics

Inbreeding depression has been recognised as a major causeof deleterious effects in individuals due to the loss of genetic variability.Nowadays, massive genotyping technologies and the analysisof runs of homozygosity (ROH) provide us with valuable toolsto further understand this condition. Using in silico methods, it hasbeen recently demonstrated that ROH size is correlated with thenumber of generations since the common ancestor, although experimentalstudies focused in this relation are scarce. Hereby, we characterisedthe ROH patterns of an extremely consanguineous cattlepopulation with very reliable pedigree data (5.2 ECG). For this,33 Retinta bulls (average Fped = 16.57%; ranging from 10.25%to 30.62%) were genotyped using the BOS 1 SNP Array. Recentinbreeding was estimated using data from the 3 last generations.ROH patterns were classified upon their size (0.5?1Mb; 1?2Mb;2?4Mb; 4?8Mb; 8?16Mb; >16MB). FROH values (percentage ofthe genome covered by ROHs) were also determined per size categoryand per chromosome. ROHs showed an average size of 2.17Mb (0.50 to 66.87 Mb), with 3.19 runs longer than 16Mb per individual.FROHs for the longest runs (8?16 and >16Mb) showed thehighest values, which is consistent with the recent inbreeding eventsproduced in this population. Interestingly, high FROH values werealso observed in the [1?2Mb] cluster, which may be explained bytraits fixed at the origin of the breed (50 generations ago). Theseresults were confirmed by Fped3-FROH correlation, which increasedtowards long ROHs (-0.28 in [0.5?1Mb] to 0.43 in >16Mb).Therefore, we demonstrated for the first time that the associationbetween long ROHs and generations since the common ancestoris conserved in highly inbred cattle. A further analysis showed thatFROH values were highly variable among chromosomes (rangingfrom 0.1198 in BTA21 to 0.2178 in BTA14). More interesting,remarkable differences were observed in the >16Mb runs, whereaverage FROH ranged from 0 (no runs on BTA26 and BTA29) to0.076 on BTA22. In conclusion, we demonstrated that homozygosityis unevenly distributed across the genome in an inbred cattlepopulation, potentially affecting