Estimated Breeding Values (EBVs)
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Statistics of the genetic evaluation

Genetic Parameters
Genetic parameters, including the additive genetic variance and the residual variance were estimated using the Restricted Maximum Likelihood (REML) procedure.

  • Additive Variance is variance due to the average effects (or additive effects) of the specific genetic trait.  Because parent-offspring resemblance depends upon the average effect of a single gene of interest being inherited, additive variance is thus responsible for parent-offspring alikeness.

  • Residual Variance are factors in any variance analysis that cannot be attributed to a precise cause.

  • REML is a specialized maximum likelihood estimation of the genetic output provided to you.

  • Heritability of a trait is measured by estimating the relative contributions of genetic and non-genetic differences to the total variation in a population.
    • Mathematically, heritability was defined as the proportion of additive variance over the total variance which is the sum of additive variance and residual variance.

 

Distribution of Breeding Value and Accuracy

  • The dogs with low breeding value (low OFA score means a better hip or elbow) and with higher accuracy (more related dogs measured, the higher the accuracy) are the most desirable for breeding purposes.

  • Low accuracy means that not many progeny were available to estimate the breeding value. Clearly, many of the dogs recorded in this web site will no longer be available for breeding as the OFA data base has records back 50 years.

 

Statistical Model
A two trait (hip and elbow OFA score) mixed linear model was employed to estimate variance components (additive genetic variance and residual variance) and to predict estimated breeding values for each dog in the pedigree.

  • Of 1,215,969 records, 92 breeds were analyzed.

  • For most breeds, there was little variation in elbow score (almost all were scored as normal).

  • Breeds with <10 records scored as abnormal for elbow dysplasia and were removed to increase accuracy of estimation, leaving only 35 breeds with elbow information.  There were 984,940 records on 982,661 unique dogs with 965,196 hip dysplasia records for 92 breeds, and 211,064 elbow dysplasia records for 35 breeds.

  • Accuracy of the breeding value was indicated by R-Square: R2=Square root (1-prediction error variance/genetic variance).