AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

PHENOTYPIC CORRELATION

• The association between two characters that can be directly observed is the correlation of phenotypic values or phenotypic correlation (r_P).
• It measures the strength of the relationship between phenotypic value in one trait and phenotypic value in another trait.
• In genetic studies the phenotypic correlation is partitioned into genetic (r_A) and environmental (r_E) correlations.
• The phenotypic correlation is determined from measurements of the two characters in a number of individuals from the population.
• A correlation, whatever its nature is the ratio of the appropriate covariance to the product of the two standard deviations.
• Therefore the phenotypic correlation between two traits X and Y is

Where

• COV_P(XY) is the phenotypic covariance between X and Y traits,
• σ_P(X) and σ_P(Y) are the phenotypic standard deviations of X and Y traits.
• Here the phenotypic COV is the sum of the genetic and environmental covariance .i.e. COV_P = COV_A + COV_E