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Flashcards in Exam 4 Deck (49)
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1

Indicator Trait

A trait that may or may not be of importance itself, but is used as a means of selecting a genetically correlated trait

2

Economic Weight

The change in return expected from a one unit change in performance of a trait

3

Breeding Objective

The weighted combination of traits defining aggregate breeding value for use in a selection index

4

Marker Assisted Selection

A type of indirect selection in which selection is on specific DNA sequences

5

Single Trait Selection

Selection for one trait

6

Tandem Selection

Selection for first one trait, then another

7

Multiple Trait Selection

selection for more than one trait

8

Selection Target

A level of breeding value that is optimal in either the absolute or practical sense

9

Environmental Correlation

A measure of the strength of the relationship between environmental effects on two traits

10

Phenotypic Correlation

A measure of the strength of the relationship between performance values for two traits

11

Genetic Correlation

A measure of the strength of the relationship between breeding values for two traits

12

Effective Proportion Saved

Reflects correct selection intensity when selecting for multiple, uncorrelated traits

13

Aggregate Breeding Value

The breeding value of an individual for a combination of traits

14

Pleiotropy

Same gene(s) affecting more than one trait

15

Economic Selection Index

A combination of weighing factors and genetic information on multiple traits

16

Independent Culling Levels

Minimum standards for traits under selection with individuals failing to meet a single criterion not selected regardless of merit in other traits

17

Direct Response

Genetic change in a trait resulting from selection for that trait

18

Correlated Response

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

19

QTL

Quantitative Trait Locus

20

Categories of traits for which marker assisted selection is expected to be useful

Carcass Traits

Sex-limited Traits

21

Two causes of genetic correlations? Specify permanent or temporary cause

Pleiotropy- same gene affects both traits (permanent)

Linkage- genes affects different traits, but are close on chromosome (temporary)

22

Briefly define each direct response to selection and correlated response to selection.

Direct Response: changing 1 trait by selecting on that trait (selecting x to change x).

Correlated Response: changing 1 trait by selecting on a different trait (selecting x to change y)

23

Briefly define each direct response to selection and correlated response to selection.

Direct Response: changing 1 trait by selecting on that trait (selecting x to change x).

Correlated Response: changing 1 trait by selecting on a different trait (selecting x to change y)

24

Provide one example of when correlated response would be considered beneficial. Provide another example where correlated response would be a concern. Use specific traits for examples.

Beneficial: increasing scrotal size in bulls decreases puberty age in daughters

Concern: increasing yearling and weaning weights would increase birth weights which could cause calving difficulties

25

List the three methods of multiple trait selection discussed in class. For each method, provide one advantage and one disadvantage associated with the method.

Tandem Selection

  • Pro: easiest to implement
  • Con: least effective

Independent Culling Level:

  • Pro: select at any time
  • Con: an animal may have 1 bad trait, but excell in other traits yet still get culled for the 1 bad trait

Economic Index:

  • Pro: most effective
  • Con: Hard to calculate

26

Describe the causes of genetic correlations and correlated response to selection

Linkage and pleiotropy cause genetic correlations and correlated response to selection. Linkage refers to genes affecting each trait which are close together on a chromosome, and pleiotropy refers to the same gene or genes affecting both traits. 

27

Are positive correlations between traits always favorable? Explain.

Positive correlations are not always favorable. It is not always desired to have the two traits positively related, as one may desire a positive change in one trait and a negative change in the other trait. 

  • Positive example: Carcass weight and Mature Size; Fat thickness and Yield Grade; Milk Production and Total Energy Intake
  • Negative Example: Birth Weight and Direct Calving Ease; Average Daily Gain and Feed to Grain Ratio

28

Factors affecting Correlated Response to Selection

  • genetic correlation between traits X and Y
  • Accuracy of selection for trait X
  • Selection intensity for trait X
  • genetic variation for trait Y
  • Generation Interval

29

Why would a breeder choose to practice indirect selection for a trait rather than direct selection?

  • A trait may be too expensive to measure
  • A trait may be too dificult to measure
  • Accuracy of selection may be greater for the correlated trait
  • the correlated trait may occur much later in life
  • the correlated trait may be sex-limited

30

Describe some situation in which indirect selection might be preferable to direct selection?

  • Direct Selection- scrotal circumference
    • Correlated Response- decreased age at puberty of daughters
  • Direct Selection- days to 230
    • Correlated Response- backfat thickness
  • Direct Selection- Weaning Weight
    • Correlated Response- Yearling Weight or Slaughter Weight