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AN SC 384 > 17: Heritability and Repeatability > Flashcards

17: Heritability and Repeatability Flashcards

1
Q

What is heritability

A

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

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2
Q

Highly heritable vs lowly heritable traits

A

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

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3
Q

Genetic model for quantitative traits

A

P = u + BV + GCV + E

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4
Q

When is performance a good indicator of BV

A

With highly heritable traits

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5
Q

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

A

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

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6
Q

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

A

there is high heritability

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7
Q

Heritability (h^2) equation

A

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

Additive genetic variance/phenotypic variance

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8
Q

Heritability is the proportion of…

A

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

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9
Q

High h^2, diff in performance…

A

are largely attributable to differences in BV

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10
Q

What is narrow-sense heritability (h^2)

A

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

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11
Q

Broad-sense heritability (H^2)

A

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

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12
Q

H^2 equation

A

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

Slide 16**

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13
Q

When is broad-sense heritability useful

A

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

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14
Q

Result of outbreeding is…

A

Gain in GCV

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15
Q

Why is H^2 not a particularly useful concept

A

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

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16
Q

Alternative definition for heritability

A

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

17
Q

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

A

There is greater change in BV per unit change in P

18
Q

Range of heritability value

A

0 to 1, always positive

19
Q

Moderately heritable values

A

between 0.21 and 0.40
Below = lowly, above = highly

20
Q

How is animal performance improved for lowly heritable traits?

A

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

21
Q

What is repeatability

A

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

22
Q

Examples of repeated traits

A

Milk yield in dairy animals, racing performance in horses

23
Q

Repeatability is the…

A

correlation between repeated records for a trait in a population

r = rP1,P2

24
Q

What is producing ability

A

Performance potential of an individual for a repeated trait

25
Q

PA is a function of…

A

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

26
Q

Range of repeatability

A

-1 to +1

27
Q

With high repeatability…

A

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

28
Q

With low repeatability…

A

First record typically not good indicator of second

Single record of performance on an animal tells us very little about the animals producing ability

29
Q

High r, differences in performance…

A

are largely attributable to differences in PA

30
Q

Repeatability as a function of variability

A

slide 32

31
Q

r indicates the strength of the relationship between…

A

P and PA

32
Q

Alternative definition of repeatability

A

Amount of change in producing ability expected per unit change in phenotypic value

Regression of PA on P

33
Q

When r is high (regression)

A

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

34
Q

Repeatability depends on population-specific factors such as…

A

allele frequencies, gene variants, environmental factors

35
Q

How does repeatability help make culling decisions?

A

For highly repeatable traits, cull poor producing animals based on performance

Wait for more records for lowly repeatable trait

AN SC 384 (22 decks)

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