Genetic gain & Inbreeding

Genetic architecture of inbreeding load for survival and body weight traits in divergently selected mouse lines

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Abstract

A divergent selection experiment for birth weight environmental variability in mice has demonstrated that genetic control of phenotypic stability can be achieved through selection. Previous studies have shown that selection for homogeneity of birth weight is associated with improvements in several fitness-related traits, including litter size, embryonic and postnatal survival, fertility, and reproductive longevity, suggesting enhanced robustness and animal welfare. However, the related matings inherent to such selection schemes lead to increased inbreeding levels, which are commonly associated with reductions in performance for fitness-related traits, known as inbreeding depression. The degree of inbreeding depression experienced by an individual is determined by its recessive genetic load, originating from the latent inbreeding load accumulated in its ancestral lineage. Since ancestors differ in the potentially harmful alleles they transmit, individuals vary in their inbreeding load. This load can be estimated by decomposing overall inbreeding into partial inbreeding coefficients (PIC) attributed to specific ancestors. However, both the variation in these PICs and the additive genetic variance of inbreeding load (IL) remain poorly understood. In this context, this study aims to estimate the inbreeding depression load on survival (SUR), birth weight (BW), and weaning weight (WW) in the two divergently selected mouse lines, providing valuable insight into the genetic consequences of selection for environmental variability and informing better population management. The pedigree included the base generation and the first 10 generations of selection (13,783 mice, discrete generations). The dataset comprised those animals within the pedigree with phenotypic records: 13,197 (BW and SUR) and 11,621 (WW), all with both parents known. The classical inbreeding coefficient and mean average relatedness in the last generation were 14.53% and 13.34%, respectively. The effective population size, computed via the individual increase in inbreeding, was 72, including animals from both lines. A total of 541 common ancestors transmitted inbreeding to between 10 and 12,485 descendants (1,996,076 PICs), with 99.98% of the PICs being lower than 0.01. The inbreeding load variances were 421.61 (WW), 2.90 (BW), and 0.01 (SUR). The correlations between additive genetic and inbreeding load effects were 0.08 (WW), -0.18 (BW), and 0.02 (SUR). Despite being under an identical mating system and therefore having equivalent levels of inbreeding across generations, breeding values for IL showed clear differences between lines. The line selected for low environmental variability showed estimated breeding values that reduced WW, yet exhibited IL estimates suggesting an improvement, whereas the high-variability line displayed the opposite pattern. The results suggest that inbreeding depression depends not only on inbreeding level but also on shared ancestry and transmitted identity-by-descent segments. Selection for genetic homogeneity may have purged alleles mitigating these effects, underscoring the need to consider lineage-specific backgrounds in selection strategies.

Keywords: 2026

How to Cite:

Perdomo-González, D., Ojeda-Marín, C., Formoso-Rafferty, N., El-Ouazizi El-Kahia, L., Varona, L., Cervantes, I. & Gutiérrez, J., (2026) “Genetic architecture of inbreeding load for survival and body weight traits in divergently selected mouse lines”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285689. doi: https://doi.org/10.31274/wcgalp.23776

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