Chapter 9: Heritability and Repeatability

What does heritability tell us?

to what extent the differences we observe in animal performance are due to inheritance

Heritability =

the measure of the strength (consistency, reliability) of the relationship between performance (phenotypic values) and breeding values for a trait in a population/

With high heritability, breeding values generally:

have a large influence on phenotypic values

Larger breeding values =

larger phenotypic deviations from the mean

When heritability is high, performance is, on average:

a good indicator of breeding value

Heritability is always:

zero — ranging from 0 to 1

What is an example of traits which tend to be lowly heritable?

traits related to fertility and survivability

What is an example of traits which tend to be moderately heritable?

production traits like milk production and growth rate

What is an example of traits which tend to be highly heritable?

carcass or “product traits“ and traits that are relate to skeletal dimentions (structural size and mature body weight)

Heritability is a ___ measure?

population

Heritability varies from:

population to population and environment to environment

When individuals share genes, they also share the ___ effects of those genes?

independent

What are “independent effects of those genes”?

These are also called additive genetic effects.

• Each gene contributes a small, predictable effect to a trait

• These effects are independent of:

  • dominance (interaction between alleles at the same locus)

  • epistasis (interaction between different genes)

The correlation in breeding values in relative is due to:

their pedigree relationship

In general, when relatives exhibit ____ in a trait, the trait is quite heritable?

similar performance

When there is little more similarity in the performance of relatives than in the performance of individuals that have been randomly chosen from the population, the heritability of the trait is:

low

The closer the resemblance among relatives for a trait, the higher the trait's:

heritability

Mathematically, heritability is the:

regression of breeding value on phenotypic value

Heritability can also be thought of as a ratio of:

variances

In phenotypic selection:

the only information used to determine whether an individual is selected or not is that individual’s own performance

If heritability is low, phenotypic values generally reveal ___ about underlying breeding values?

little

When heritability is low, performance is a good indicator of:

breeding value

• accuracy of selection will be good —> genetic change should be fast

Accuracy of selection will always be:

better for a more heritable trait than for a less heritable one

Producers tend to select for:

more highly heritable traits

Why do producers select for more highly heritable traits?

since they know they can make a significant genetic change

How do producers improve lowly inheritable traits?

though management

But some traits are so important economically that:

they deserve to be selected for despite low heritability