Metafounders are related to F st fixation indices and reduce bias in single-step genomic evaluations.

CA Garcia-Baccino, A Legarra, OF Christensen, I Misztal, I Pocrnic, ZG Vitezica, RJ Cantet

Research output: Contribution to journalArticlepeer-review

Abstract

Background: Metafounders are pseudo-individuals that encapsulate genetic heterozygosity and relationships
within and across base pedigree populations, i.e. ancestral populations. This work addresses the estimation and usefulness
of metafounder relationships in single-step genomic best linear unbiased prediction (ssGBLUP).
Results: We show that ancestral relationship parameters are proportional to standardized covariances of base allelic
frequencies across populations, such as Fst fixation indexes. These covariances of base allelic frequencies can be
estimated from marker genotypes of related recent individuals and pedigree. Simple methods for their estimation
include naïve computation of allele frequencies from marker genotypes or a method of moments that equates average
pedigree-based and marker-based relationships. Complex methods include generalized least squares (best linear
unbiased estimator (BLUE)) or maximum likelihood based on pedigree relationships. To our knowledge, methods
to infer Fst coefficients from marker data have not been developed for related individuals. We derived a genomic
relationship matrix, compatible with pedigree relationships, that is constructed as a cross-product of {−1,0,1} codes
and that is equivalent (apart from scale factors) to an identity-by-state relationship matrix at genome-wide markers.
Using a simulation with a single population under selection in which only males and youngest animals are genotyped,
we observed that generalized least squares or maximum likelihood gave accurate and unbiased estimates of
the ancestral relationship parameter (true value: 0.40) whereas the naïve method and the method of moments were
biased (average estimates of 0.43 and 0.35). We also observed that genomic evaluation by ssGBLUP using metafounders
was less biased in terms of estimates of genetic trend (bias of 0.01 instead of 0.12), resulted in less overdispersed
(0.94 instead of 0.99) and as accurate (0.74) estimates of breeding values than ssGBLUP without metafounders and
provided consistent estimates of heritability.
Conclusions: Estimation of metafounder relationships can be achieved using BLUP-like methods with pedigree and
markers. Inclusion of metafounder relationships reduces bias of genomic predictions with no loss in accuracy.
Original languageEnglish
JournalGenetics Selection Evolution
DOIs
Publication statusPublished - 10 Mar 2017

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