Selection

Question 1

Selection

Answer 1

Humans most effective means to influence rate of genetic change

Question 2

Rate of genetic change with Selection

Answer 2

1) Heritability
2) Selection Differential
3) Population Size
4) Generation Interval

Question 3

Heritability in Selection

Answer 3

Higher h2 = faster rate of change

Question 4

Selection Differential in Selection

Answer 4

mean value of selected individuals - mean value of population from which they were selected

Question 5

Population size in Selection

Answer 5

greater size = greater superiority
[more change for variation]

Question 6

Basis for Selection

Answer 6

1) Individual performance
2) Pedigree (ancestors)
3) Collateral relatives (full sib vs half sibs)
4) Progeny (very powerful)

Question 7

Accuracy of Selection

Answer 7

Measurement of the relationship between true breeding values and the predicted breeding values

Question 8

Relative reliability of estimate

Answer 8

Statistically: Estimate of how accurately the genotype of the individual for a certain trait can be predicted from the phenotypic averages of it’s relatives

Will change over time (more information about the population as it changes will shift accuracy)

Question 9

Selection Intensity

Answer 9

Measurement of how “choosy” breeders are in deciding what animals will become parents

[High selection intensity means to choose only best individuals ]

Question 10

Generation Interval

Answer 10

Average age of the breeding herd when their selected offspring are born

Question 11

Individual performance

Answer 11

Record from a single animal
Value highly related to h2

Disadvantages:
1) sex limited trait
2) traits requiring long tome
3) carcass traits
4) low h2 traits (=low accuracy)

Question 12

Pedigree

Answer 12

Information based on ancestor performance
a) degree of relationship
b) h2 of trait
c) environmental correlation between ancestor and individual (must be high)

Question 13

Pedigree Advantages

Answer 13

1) Cheap
2) Valuable for sex-limited traits
3) Valuable for traits expressed later in life
4) Low h2 traits

[Attention to records of ancestors increases accuracy of selection]

Question 14

Pedigree disadvantages

Answer 14

1) Lack of accurate records/environmental influences of ancestors performance records
2) Provides no comparative basis for selection among individuals that are all descendants of the same ancestor

Question 15

Collateral Relatives

Answer 15

Looks at sibling relationship
Value:
1) Sex-limited traits
2) Traits that require slaughter to measure
3) Accuracy tends to be lower than individual performance

Question 16

Factors affecting accuracy of sib test [Collateral Relatives]

Answer 16

1) h2 of traits
2) Relationship of sib
3) Number of sibs tested (More # = more accurate)
4) Correlation between phenotypes of sibs
[Environmental correlation, including maternal environment]

Question 17

Progeny Testing with Qualitative Traits

Answer 17

Objective: help determine likelihood that an animal is a carrier of detrimental recessive
Factors of “success” of test:
1) genetic makeup of test animal
2) number of offspring that can be produced

Question 17

Progeny Testing

Answer 17

The evaluation of the genetic makeup of an individual by phenotypic of its progeny

Genetic worth of an animal= Qualitative and Quantitative traits

Question 18

Progeny Testing with Quantitative Traits

Answer 18

Objective: to determine breeding value of parents
Basis for EPD and EBV

As h2 increases, more progeny required to equal accuracy of individual performance

Question 19

Factors affecting accuracy of progeny test for quantitative traits

Answer 19

• Dams must be random
• Offspring tested in same environment
• Compare parents of similar age and environment
  -Increase number of progeny = increased accuracy

Question 20

Selection of more than one trait

Answer 20

Net value of animal dependent on several traits (May not be of equal economic value or independent of one another)

Three methods: (plus 1)
-Tandem
-Independent culling
-Selection index
[-BLUP]

Question 21

Tandem

Answer 21

Selection for one trait at a time (start with one and build up)
Problems:
-Genetic relationship between traits
-more traits = slower progress (takes longer)

Question 22

Selection Index

Answer 22

Def: A single number that predicts the breeding value of an individual for a weighted combination of traits

Place different degrees of emphasis on traits of interest
Separate determination of the value for each trait selected for, then the addition of these values gives a total score

Question 22

Independent Culling Method

Answer 22

Minimal standard for each trait
If minimum isn’t reached for any trait trait, animal is culled
Problem: Potential to cull animals outstanding in one trait just because another didn’t meet the requirements

Question 23

BLUP

Answer 23

Best Linear Unbiased Prediction
[Extension of Selection Index]
Method of genetic prediction (for selection) particularly appropriate when performance data come from genetically diverse contemporary groups

Question 24

Keys for Selection Based on More than One Trait

Answer 24

1) Genetic relationship among traits
2) Number of traits selected for
3) h2 of traits