Chapter 13: Correlated Response to Selection

Comprehensive vocabulary flashcards covering the concepts, equations, causes, and multiple-trait selection methods associated with correlated response to selection.

Correlated Response to Selection

Genetic change in one or more traits resulting from the selection for another trait.

Pleiotropy

A biological phenomenon where a single gene affects more than one trait; one of the two primary causes of correlated response to selection.

Linkage

One of the two primary biological causes of correlated response to selection, occurring alongside pleiotropy.

Genetic Correlation

From a statistical perspective, a measure of the strength, consistency, and reliability of the relationship between breeding values for one trait and breeding values for another trait, or a measure of the relative importance of pleiotropic effects on two traits.

Phenotypic Correlation ($r_{P_X,P_Y}$)

A measure of the strength, consistency, or reliability of the relationship between performance in one trait and performance in another trait.

Environmental Correlation ($r_{E_X,E_Y}$)

A measure of the strength, consistency, or reliability of the relationship between environmental effects on one trait and environmental effects on another trait.

Direct Selection

Selection for a trait as a means of improving that same trait.

Indirect Selection

Selection for one trait as a means of improving a genetically correlated trait.

Indicator Trait

A trait that may or may not be important in itself, but is selected for as a way of improving some other genetically correlated trait.

Tandem (Serial) Selection

A multiple-trait selection method in which selection is practiced for one trait until a predetermined target level is reached, followed by selection for another trait.

Independent Culling

A multiple-trait selection method in which minimum standards are set for each trait, and any animal failing to meet any single standard is culled.

Breeding Objective

A weighted combination of traits used to define net merit (aggregate breeding value) in defining a selection index.

Phenotypic Selection Index

A selection index form expressed as $I = b_1x_1 + b_2x_2 + b_3x_3 + b_4x_4 \dots$ that uses individual phenotypic information exclusively to predict aggregate breeding value.

Economic Selection Index

A multi-trait index yielding a single numerical value that predicts overall economic merit by weighting breeding values only for traits that carry economic impact.

Rate of Correlated Genetic Change ($\Delta_{BV_{Y|X}}/t$)

The rate of genetic change in trait $Y$ per unit of time ($t$) resulting from selection for trait $X$, calculated as $\frac{r_{BV_X, BV_Y} r_{BV_X, \hat{BV}_X} i_X \sigma_{BV_Y}}{L}$.

Ratio of Response

The ratio comparing the efficiency of indirect selection for a trait to direct selection for that trait, expressed as $\frac{\Delta_{BV_{Y|X}}}{\Delta_{BV_Y}} = \frac{r_{BV_X,BV_Y} r_{BV_X,\hat{BV}_X} i_X}{r_{BV_Y,\hat{BV}_Y} i_Y}$.

Three Correlation Considerations

The three critical factors evaluated when interpreting genetic, phenotypic, and environmental correlations: 1. Direction, 2. Strength, and 3. Favorable vs. Unfavorable.

Feed Conversion (FC)

A performance measure calculated as $\frac{\text{lbs. feed}}{\text{lbs. gain}}$, having a positive genetic correlation with days to $230\,\text{lb}$ and a negative genetic correlation with weight per day of age in swine.