FEATURE ARTICLE
GENETIC EVALUATIONS, HISTORY AND IMPROVEMENTS: PART 1 – GENOMIC RELATIONSHIPS by JR Tait, Ph.D., director of genetics product development, Neogen Genomics, Lincoln, Nebraska and Jamie Courter, Ph.D., beef product manager, Neogen Genomics, Lincoln, Nebraska Genetic evaluation systems which brought us Expected Progeny Differences (EPDs) leverage variations in performance of individual animals from their contemporaries and expected relationships between those individual animals based on the pedigree relationship amongst animals. These expected relationships are both the average relationship and the most commonly observed relationships. However, the fact that each calf inherits a random half of the sire’s DNA combined with a random half of its dam’s DNA means that the true relationships between animals may equal those expectations, or they may be different. The benefit of genomics is that they tell us what those relationships actually are between individual animals instead of an assumption.
The pedigree expected relationship between all full sib calves is that they share 0.50 (50%) of their DNA with each other. This expectation is often correct, but in reality there is variability around that expectation. In Figure 1 the relationships between calves within some of the potential calf combinations are: Calf 1 to Calf 2 = 0.50; Calf 1 to Calf 3 = 0.50; Calf 1 to Calf 4 = 0.00; Calf 2 to Calf 3 = 0.00; Calf 2 to Calf 4 = 0.50; Calf 3 to Calf 4 = 0.50. In this case Figure 1 only shows 4 potential calves, which are only 25% of the 16 possible combinations of calves. There are (number of pairs chromosomes)2 combinations of the chromosomes possible from each parent; in this example that is 22 = 4 chromosome combinations from the sire and 4 combinations
Figure 1. Chromosomal inheritance example simplified to 2 pairs of chromosomes. In these examples the chromosome on the left is from the sire of the individual and the chromosome on the right is from the dam of the individual. 52
March 2022
