Characterizing and Eliminating the Inbreeding Load

Abstract

The authors evaluated the relevant literature related to purging, which is the interaction between selection and inbreeding in which the population may eliminate its inbreeding load at least partially. According to the relevant literature, the inbreeding load and the process of purging were evaluated via pedigree methods based on ancestral inbreeding, the inbreeding-purging model, and expressed opportunity of purging, along with genomic methods. Most ancestral inbreeding-related studies were performed in zoos, where only a small proportion of the studied populations show signs of purging. The inbreeding-purging model was developed with Drosophila, and it was used to evaluate different zoo ungulates and Pannon white rabbits. Purging was detected in both studies. The expressed opportunity of purging was applied in Jersey cattle and Pannon white rabbits. In the Jersey cattle, it had an effect of 12.6% for fitness, while in the Pannon white rabbits, the inbreeding load was between 40% and 80% of its original value. The genomic studies also signalled purging, but they also made it clear that, contrary to the detected purging, the evaluated populations still suffered from inbreeding depression. Therefore, especially for domesticated animals, it can be concluded that deliberate inbreeding with the purpose of generating purging is not advocated.

Keywords: ancestral inbreeding; inbreeding–purging model; lethal equivalent; new inbreeding; old inbreeding; purged inbreeding coefficient; purging; purging coefficient.

Figure 1

Evolution of the different dam and litter inbreeding coefficients of the Pannon white rabbits (Wright: a,b; Ballou: c,d; Kalinowski: e,f; Kalinowski new: g,h) [61].

Figure 2

Evolution of the standard (F, red) and purged (g, green) inbreeding coefficients through time [45].

Figure 3

Evolution of the early survival [45] (large dots represent mean Ws, while small dots correspond to the mean value plus or minus one standard error).

Figure 4

The predicted fitness based on the Wright (F) and on the purged (g) inbreeding coefficients [94].