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. 2019 Aug;212(4):1075-1099.
doi: 10.1534/genetics.119.302375. Epub 2019 Jun 17.

A Unified Model for Inclusive Inheritance in Livestock Species

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A Unified Model for Inclusive Inheritance in Livestock Species

Ingrid David et al. Genetics. 2019 Aug.

Abstract

For years, animal selection in livestock species has been performed by selecting animals based on genetic inheritance. However, evolutionary studies have reported that nongenetic information that drives natural selection can also be inherited across generations (epigenetic, microbiota, environmental inheritance). In response to this finding, the concept of inclusive heritability, which combines all sources of information inherited across generations, was developed. To better predict the transmissible potential of each animal by taking into account these diverse sources of inheritance and improve selection in livestock species, we propose the "transmissibility model." Similarly to the animal model, this model uses pedigree and phenotypic information to estimate variance components and predict the transmissible potential of an individual, but differs by estimating the path coefficients of inherited information from parent to offspring instead of using a set value of 0.5 for both the sire and the dam (additive genetic relationship matrix). We demonstrated the structural identifiability of the transmissibility model, and performed a practical identifiability and power study of the model. We also performed simulations to compare the performances of the animal and transmissibility models for estimating the covariances between relatives and predicting the transmissible potential under different combinations of sources of inheritance. The transmissibility model provided similar results to the animal model when inheritance was of genetic origin only, but outperformed the animal model for estimating the covariances between relatives and predicting the transmissible potential when the proportion of inheritance of nongenetic origin was high or when the sire and dam path coefficients were very different.

Keywords: inclusive inheritance; livestock; model.

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Figures

Figure 1
Figure 1
Path coefficient diagram describing the transmission of the different inherited factors in livestock species. a, genetic effects; epi, epigenetic effect; mic, microbiota effect; cult, cultural effect; y, phenotype; e, residual. Indices s, d, o and i refer to sire, dam, offspring, and comate i, respectively.
Figure 2
Figure 2
Profile likelihood vs. parameters to estimate in a model designed to disentangle genetic and epigenetic effects and in the transmissibility model. The true model is yi=ai+epii+ei. The values of the true model are H2=σa2+σepi2σa2+σepi2+σe2=0.4, r = σa2σa2+σepi2=0.5, and six different combinations for the epigenetic path coefficient of transmission are considered. The two models of estimation are yi=ai+epii+ei (mod1) and the transmissibility model yi=ti+ei. First four left panels: profile likelihoods for the parameters H02, r0,λs0, and λd0 for mod1. Three last panels: profile likelihoods for τ02,ωs0, and ωd0. Top to bottom: small, medium, and large pedigree sizes; colors of lines: different values of the combination λs, λd. Dotted horizontal line: the χ2 threshold value.
Figure 3
Figure 3
Power to detect nongenetic inheritance with a transmissibility model considering equal path coefficients of transmission for the sire and the dam. The true model is yi=xiβ+ai+epii+ei, considering same sire and dam epigenetic path coefficients of transmission (λ=λs=λd). Values of the true model are H2=σa2+σepi2σa2+σepi2+σe2=0.2,0.4 or 0.6, r = σa2σa2+σepi2=0.3,0.5, or 0.7 and varying values for the path coefficient of transmission λ [0.05,0.5]. The model of estimation is the transmissibility model yi=xiβ+ti+ei, which considers the same path coefficients of transmission for the sire and the dam (ωd=ωs=ω). The null hypothesis H0 is ω=0.5, the alternative hypothesis is H1 ω0.5.
Figure 4
Figure 4
Power to detect nongenetic inheritance with the transmissibility model considering different path coefficients of transmission for the sire and the dam. The true model is yi=xiβ+ai+epii+ei. Values of the true model are H2=σa2+σepi2σa2+σepi2+σe2=0.2,0.4, or 0.6, r = σa2σa2+σepi2=0.3, 0.5, or 0.7 and varying values for the sire and dam epigenetic path coefficient of transmission λs [0.05,0.5]andλd[0.05,0.5].  The model of estimation is the transmissibility model yi=xiβ+ti+ei . The null hypothesis H0 is ωd=ωs=0.5, the alternative hypothesis is H1 ωd0.5 or ωs0.5
Figure 5
Figure 5
Sire and dam transmissibilities estimated using the animal and transmissibility models for the different datasets. Dotted lines show the simulated values.
Figure 6
Figure 6
Ratio of regression coefficient between relatives to simulated regression coefficient estimated by the animal and transmissibility models for the different datasets. The types of relatives are: 1, paternal grand dam-offspring; 2, maternal grand dam-offspring; 3, paternal half-sib of the sire (paternal uncle 1)-offspring; 4, maternal half-sib of the sire (paternal uncle 2); offspring; 5, paternal half-sib of the dam (maternal uncle 1)-offspring; 6, maternal half-sib of the dam (maternal uncle 2)-offspring; 7, paternal half-sibs; 8, full-sibs.

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