17: Heritability and Repeatability

Question 1

What is heritability

Answer 1

Measures the degree to which offspring resemble their parents in performance for a trait

Question 2

Highly heritable vs lowly heritable traits

Answer 2

High = animals with high performance tend to produce high performing offspring and vice versa
Low = performance records of parents reveal little about progeny performance

Question 3

Genetic model for quantitative traits

Answer 3

P = u + BV + GCV + E

Question 4

When is performance a good indicator of BV

Answer 4

With highly heritable traits

Question 5

Definition of heritability with respect to the relationship between P and BV

Answer 5

Measure of the strength of the relationship between performance and breeding values for a trait in a population

Question 6

If phenotypic value and breeding value are similar (strong, consistent relationship) then…

Answer 6

there is high heritability

Question 7

Heritability (h^2) equation

Answer 7

h^2 = COV(P,BV)/Vp

Additive genetic variance/phenotypic variance

Question 8

Heritability is the proportion of…

Answer 8

differences in performance for a trait that are attributable to differences in BV for the trait

Question 9

High h^2, diff in performance…

Answer 9

are largely attributable to differences in BV

Question 10

What is narrow-sense heritability (h^2)

Answer 10

Strength of the relationship between phenotypic values and breeding values for a trait in a population

Question 11

Broad-sense heritability (H^2)

Answer 11

Strength of the relationship between phenotypic values and genotypic values for a trait in a population

Question 12

H^2 equation

Answer 12

Broad-sense H = V(A)+V(GCV)/V(P)

Slide 16**

Question 13

When is broad-sense heritability useful

Answer 13

For traits with low h^2, use of GCV effects through outbreeding is a viable option and H^2 assesses magnitude of total genetic contribution

Question 14

Result of outbreeding is…

Answer 14

Gain in GCV

Question 15

Why is H^2 not a particularly useful concept

Answer 15

GCV cannot be inherited, and H^2 does not reflect the relationship between the performance of animals and their potential as parents

Question 16

Alternative definition for heritability

Answer 16

Amount of change in BV expected per unit change in phenotypic value
(regression of BV on P)

Question 17

When h^2 is high (regression of BV on P)

Answer 17

There is greater change in BV per unit change in P

Question 18

Range of heritability value

Answer 18

0 to 1, always positive

Question 19

Moderately heritable values

Answer 19

between 0.21 and 0.40
Below = lowly, above = highly

Question 20

How is animal performance improved for lowly heritable traits?

Answer 20

Through management, NOT selection
e.g. improve fertility by providing good nutrition

Question 21

What is repeatability

Answer 21

Measure the strength of relationship between repeated records (repeated phenotypic values) for a trait in a population

Question 22

Examples of repeated traits

Answer 22

Milk yield in dairy animals, racing performance in horses

Question 23

Repeatability is the…

Answer 23

correlation between repeated records for a trait in a population

r = rP1,P2

Question 24

What is producing ability

Answer 24

Performance potential of an individual for a repeated trait

Question 25

PA is a function of...

Answer 25

All those factors that permanently affect an individual's performance potential (genotypic value and permanent environmental effects)

Question 26

Range of repeatability

Answer 26

-1 to +1

Question 27

With high repeatability...

Answer 27

First record on an animal is, on average, a good indicator of that animals second record Single record of performance on an animal is, on average, a good indicator of that animal's producing ability

Question 28

With low repeatability...

Answer 28

First record typically not good indicator of second Single record of performance on an animal tells us very little about the animals producing ability

Question 29

High r, differences in performance...

Answer 29

are largely attributable to differences in PA

Question 30

Repeatability as a function of variability

Answer 30

slide 32

Question 31

r indicates the strength of the relationship between...

Answer 31

P and PA

Question 32

Alternative definition of repeatability

Answer 32

Amount of change in producing ability expected per unit change in phenotypic value Regression of PA on P

Question 33

When r is high (regression)

Answer 33

there is greater change in producing ability per unit change in phenotypic value

Question 34

Repeatability depends on population-specific factors such as...

Answer 34

allele frequencies, gene variants, environmental factors

Question 35

How does repeatability help make culling decisions?

Answer 35

For highly repeatable traits, cull poor producing animals based on performance Wait for more records for lowly repeatable trait