Genetic load components and kinship load
We analysed the genetic load in the hypothetical offspring of our six pink pigeons. This kinship load is calculated by theoretically crossing all possible combinations of individuals assuming mendelian segregation ratios. As kinship between two individuals increases, homozygosity of their offspring increases (Figure 3). Similarly, increased kinship between parents elevates offspring’s’ realised load and reduces masked load (Figure 3). Optimal mate pairing can significantly reduce the realised load of the offspring (R2=0.258, F1,13 = 8.32, p=0.00918).
Next, we performed an analysis to identify optimal crosses to minimise genetic load (Figure 4). Figure 4A shows average genetic load of potential offspring. In essence, these are the deleterious mutations that offspring are predicted to inherit from both parents, with blue tiles representing offspring with low genetic load, and red tiles offspring with high genetic load. The genetic load is lowest in the offspring from a cross between individuals 2 and 3.
To predict degree of inbreeding depression, the realised load of the offspring of different crosses was calculated. Blue tiles in the correlogram in Figure 4B show the realised load of the offspring of the optimal crosses. The realised load of these offspring is 7.4% less than that of offspring of random crosses (Figure 4E), and these offspring are predicted to show less inbreeding depression. Note that the offspring from the 2 x 3 cross with the lowest genetic load possesses a relatively high realised load. Individuals 2 and 3 were closely related (Aunt and Niece), but they each possess a low genetic load. However, because they are related, their offspring expresses a high realised load, even though their genetic load is low.