18: Repeatability and Correlations

Question 1

Slide 11, 12

Answer 1

Repeatability as a function of variability

Question 2

Order from largest to smallest: r, H^2, h^2

Answer 2

h^2 </= H^2</= r

Question 3

Why is narrow sense heritability the smallest value

Answer 3

Least amount of factors in the numerator
slide 18

Question 4

With high h^2…

With high r…

Answer 4

prediction of BV will be more accurate

prediction of PA will be more accurate

Question 5

Higher h^2 and higher r lead to fewer mistakes in… respectively

Answer 5

replacement selection, culling

Question 6

What is correlation

Answer 6

Function of covariance between two values and their standard deviations

Indicates consistency and reliability of the relationship

Question 7

Range of correlation

Answer 7

+1 (very strong and positive) to -1 (very strong and negative)

Question 8

What is phenotypic correlation

Answer 8

Association between two traits that can be directly observed
Strength of relationship btw phenotypic value in one trait and phenotypic value in another

Question 9

What is environmental correlation

Answer 9

Measure of the strength of the relationship between environmental effects on one trait and environmental effects on another trait

Question 10

Environmental correlation considers…

Answer 10

environmental deviations together with non-additive genetic deviations between two characters

Question 11

What is environmental correlation used for? Example

Answer 11

Management purposes
e.g. environmental correlation between average daily gain and back-fat thickness in swine has been estimated at +0.40

Suggest environments conducive to rapid weight gains tend to produce fatter pigs

Question 12

What is genetic correlation

Answer 12

Quantify the overall genetic similarity between complex traits

Measures the strength of the relationship between breeding values for one trait and breeding values for another trait

Question 13

Slides 25-27

Answer 13

Types of correlation

Question 14

Two ways genes would be gentically correlated? Describe

Answer 14

Pleiotropy: a single gene affects two or more different traits

Linkage: different loci influencing distinct traits are situated close together on the same chromosome, preventing independent segregation during meiosis phase of sexual reproduction

Question 15

Example of pleiotropy

Answer 15

Two loci variants (IGF-1 and HMGA2) for small body size associated with separation anxiety, touch sensitivity, owned directed aggression and dog rivalry

Selected for size; unintentionally selected for behaviour

Question 16

Why is understanding genetic correlation important? E.g.

Answer 16

If two traits are genetically correlated, selection for one will cause genetic change in the other

e.g. selection to improve scrotal circumference will result in reduced age at puberty (female trait)

Question 17

Describe the selective breeding for tameness project in foxes

Answer 17

Started in 1959 by Dr. Dmitri Belyaev
Wanted to understand process of domestication by direct selection of behavioural traits on silver foxes
Would cross tame to tame and aggressive to aggressive
Saw behavioural changes in tame (approachability, tail wagging) and also morphological changes (floppy ears, curly tail, coat colour variations)

Question 18

Different ways correlation between traits can be classified

Answer 18

Strength: strong or weak
Sign/direction: positive or negative
Favourable or unfavourable

Question 19

Example of positive correlation and negative correlation

Answer 19

Pos: positive correlation between birth weight and calving dystocia is unfavourable since heavier calves are associated with higher calving problems

Neg: negative correlations between yearling weight and age at puberty is favourable since heavier animals at yearling will likely have lower age at puberty

Question 20

Correlation varies from… E.g.

Answer 20

population to population

Correlation between milk production and fertility may be quite different in two different breeds of cattle

Question 21

Different levels of correlation strength

Answer 21

None: 0-0.1
Weak: 0.1-0.3
Moderate: 0.3-0.5
Strong: 0.5+

(same in negative direction)

Question 22

Additional applications of correlation

Answer 22

• predict genetic change in one or more traits from selection for another trait (correlated response to selection)
• provide additional source of info for the prediction of BVs
• used for construction of multi-trait selection indices