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Changes to Scaling of Genomic Inbreeding


CDCB routinely distributes pedigree-based and genomic-based inbreeding values. With the April 2021 evaluations, revisions were made in the scaling of genomic inbreeding to account for X chromosome differences between males and females.
 
What are the key takeaways?

  • Changes implemented in April evaluations impacted the scaling and comparability across sexes; changes did not affect the ranking for genomic inbreeding within either sex.
  • Revisions did not affect animals’ PTAs (Predicted Transmitting Abilities), except in unique cases. There were slight adjustments to reliabilities for some animals.
  • Genomic inbreeding values of males and females are now more comparable to each other and to pedigree inbreeding.
  • Computation has been improved to more rapidly process the larger numbers of genotypes expected in the future.

What was the change made?
In cattle (and humans), the inheritance of the X chromosome is different between sexes. Males have one copy of X and one of Y, whereas females have 2 copies of X.
 
Because males were predominantly genotyped in the early phases of genomics, the genomic inbreeding was originally scaled to match pedigree inbreeding using males. In recent years, genotyping of females increased drastically. Until now, the scaling of genomic inbreeding values included females but did not account for the differences in the X chromosome between sexes.

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