Genetic Value Analysis

The genetic value analysis proceeds according to the following steps:

  1. First, the average of all pairwise kinship coefficients are calculated for each living animal in the breeding colony relative to every other living animal in the colony according, to the algorithm of Lange (2002). The grand mean kinship in the breeding colony is then calculated from the distribution of individual mean kinships, along with other summary statistics describing this distribution.
  2. Second, measures of individual mean kinship for each animal are then calculated in terms of standard deviates from this grand mean kinship, as z = (x-μ)/σ, i.e., "z-scores", in which x is the estimate of individual mean kinship, μ is the grand mean kinship, and σ is the standard deviation of the distribution of all individual mean kinship values of living animals in the colony.

    These z-scores indicate the extent and direction to which each animal's individual mean kinship deviates from the grand mean kinship in the colony. An animal having a positive z-score has individual mean kinship that lies above the colony grand mean kinship, suggesting that this animal's genome is over-represented in the colony, making the animal of lesser genetic value than others with negative z-scores. Conversely, an animal having a negative z-score has individual mean kinship that lies below the grand mean kinship, suggesting that this animal's genome is underrepresented in the colony, making the animal of greater genetic value than animals with positive z-scores.

  3. Third, genome uniqueness values are calculated using a gene-drop simulation according to MacCluer et al. (1986) and Ballou & Lacy (1995), by assigning unique alleles to all pedigree founders, and simulating their segregation throughout the pedigree according to Mendelian rules. Genome uniqueness is a measure of the probability that an animal possesses founder alleles that are present in at most x other animals (usually 0-3), and thus are rare and at risk of being lost from the population. A range of 2 to 100,000 simulations may be selected. A minimum of 1,000 simulations is recommended. A genome uniqueness threshold value between 0-3 should also be selected, as desired.
  4. Following the calculation of mean kinship, related z-scores, and genome uniqueness for all animals, animals are ranked from the highest genetic value (ranking = 1) to the lowest, according to the following rules:
    1. Imported animals without offspring are automatically ranked highest in genetic value, followed by
    2. All animals with greater than 10% genome uniqueness, ordered first by genome uniqueness from largest to smallest values, and by z-score within the same genome uniqueness from smallest to largest values; followed by
    3. All remaining animals (those with = 10% genome uniqueness), ranked by z-score from smallest to largest values; followed by
    4. A threshold drawn at those animals with genome uniqueness = 10% and z-scores = 0.25. Animals falling below this threshold are indicated by highlighting in the results. Animals ranking above this threshold are considered to be of high genetic value, while animals that rank below this threshold are not recommended for breeding, but may be suitable for research assignment or sale.

Breeding Group Formation