Exam 2 Flashcards
What is the new equation for phenotype?
P = BV + D + I + Ep + Et
D=dominance effect
I=epistatic effect
What kind of estimate is heritability?
Population
What is heritability?
Relationship of the difference in animal performance due to inheritance
How does heritability vary?
Population to population and environment to environment
What are the 2 types of heritability?
Broad sense (H^2) Narrow sense (h^2)
What is broad sense heritability?
Measure of the strength of the relationship between performance and genotypic value for a trait in a population
How is broad sense heritability denoted?
H^2 = r^2p,g r^2p,g = correlation between p and g
What is broad sense heritability used in?
Identical individuals
What is narrow sense heritability?
Measure of the strength of the relationship between performance and breeding values for a trait in a population
Hos is narrow sense heritability denoted?
h^2 = r^2p,bv r^2p,bv = correlation between p and BV
What is narrow sense heritability used in?
Animal production
What does broad sense include?
BV plus GCV or dominance and epistatic effects
What does narrow sense include?
BV
Why is GCV not included in narrow sense?
GCV cannot be inherited
What is the range of narrow sense heritability?
0 to 1
What are the ranges for low, moderate, and high heritability?
Less than 0.2 is low heritability
0.2-0.4 is moderate heritability
More than 0.4 is high heritability
What is parental performance when there is high h^2?
A good indicator of offspring performance
What does parental performance do when there is low h^2?
Reveals little about offspring performance
What are examples of trait estimates for fitness?
Fertility and survivability
What is heritability like for fitness?
Low h^2
What are examples of trait estimates for production?
Milk production and growth rate
What is heritability like for production?
Moderate h^2
What are examples of trait estimates for terminal?
Carcass
Skeletal
Mature weights
What is heritability like for terminal?
High h^2
What is the alternative definition for narrow sense?
h^2 = Va / Vp = Va / (Va + Vd + Vi + Vep + Vet)
When there is a high environmental effect, what is heritability like?
Low
When there is a low environmental effect, what is heritability like?
High
What is the objective for heritability and selection?
To choose an individual with the best breeding value
In phenotypic selection, what does performance reveal when there is low heritability?
Little about breeding value
What is genetic change like in phenotypic selection with low heritability?
Slow
In phenotypic selection, what does performance reveal when there is high heritability?
It is a good indicator about breeding value
What is genetic change like in phenotypic selection with high heritability?
Fast
What is heritability used in the prediction of?
BV
PD
PA
What does heritability and predictions indicate?
How conservative a prediction should be
What traits do producers tend to select?
More highly heritable traits that can make significant change
What do large differences in performance lead to?
Large differences in BVs
What do producers choose not to change low heritable traits through?
Management
What kind of estimate is repeatability?
Population
How does repeatability vary?
From population to population and environment to environment
What is repeatability a measure of?
The strength of the relationship between repeated records for a trait in a population
What is repeatability denoted as?
r = r_p1,p2
What is the range of repeatability?
-1 to 1
What are the ranges for low, moderate, and high repeatability?
Less than 0.2 is low repeatability
0.2-0.4 is moderate repeatability
More than 0.4 is high repeatability
If repeatability is high, what is the the first record used as?
A good indicator for the 2nd record
If repeatability is low, what is the the first record for the 2nd record?
A poor indicator of the 2nd record
What traits are used for repeatability?
Traits that have more than one performance record
What is the alternate definition for repeatability?
r = (Va + Vd + Vi + Vep) / (Va + Vd + Vi + Vep + Vet)
What is repeatability like when there is a low temporary environmental effect?
High
What is repeatability like when there is a high temporary environmental effect?
Low
For culling purposes, what should you do when there is high repeatability?
Cull poor producing animals
For culling purposes, what should you do when there is low repeatability?
Get more records before making a decision
What does repeatability become when predicting producing abilities?
Adjustment factor
What are 3 ways to improve heritability and repeatability?
Environment uniformity
Accurate measurement
Contemporary groups
What do you want in environment uniformity?
Environment the same for different animals
Not making the environment better, just similar
When using accurate measurements, what do you adjust for?
Known environmental effects
What are some known environmental effects?
Age of dam Age of animal Sex of animal Parity Milkings per day
What are contemporary groups?
Groups of animals that have experienced a similar environment with respect to the expression of a trait
How do you compare contemporary groups?
As a deviation from the group mean
p – p_cg
How many animals do you want in a contemporary group?
5 or more
What is the new model for P with contemporary group?
P = μ + BV + GCV + Ecg + E
What is the equation with contemporary group for BV and PA?
P – Pcg = BV + GCV + Ep + Et
P – Pcg = PA + GCV + Ep + Et
What is a trait ratio?
Ratio of an individual’s performance to the average performance of all individuals in the contemporary group
How do you calculate the ratio?
(Pi / Pcg) x 100
What are the 4 factors of genetic change?
Accuracy of selection
Selection intensity
Genetic variation
Generation interval
What is the symbol for the rate of genetic change or response to selection?
ΔBV/t
What is the symbol for accuracy of selection?
r_bv, bv(hat)
What does selection intensity measure?
How “choosy” breeders are in selecting individuals
If there is a high intensity, what does the at say about selecting animals?
Selecting very best animals
If there is no intensity, what does the at say about selecting animals?
Selecting animals at random
What is the symbol for selection intensity?
i
How do you calculate selection intensity?
(SCs – SC) / σsc
What is the rate of genetic change like when accuracy and intensity are low?
Slow
What is the rate of genetic change like when accuracy and intensity are high?
Fast
What is genetic variation?
Variability of BV within a population for a trait
What is the symbol for genetic variation?
σ_BV
What is generation interval?
Amount of time required to replace one generation with the next
In closed populations, what is generation interval defined as?
The average age of parents when their offspring are born
What is the symbol for generation interval?
L
What is the equation for genetic change?
(r_bv, bv(hat) x i x σ_BV) / L
What is the equation for genetic change with phenotypic selection?
(h^2 x i x σ_p) / L
What is the equation for genetic change when there is a male and female involved?
(h^2 x (im + if) x σ_p) / (Lm + Lf)
If L decreases, what happens to other factors?
They decrease
If accuracy increases, what happens to intensity?
It decreases (and vice versa)
If you test fewer males, is there more or less to select from? What does having fewer males mean for females?
There’s less to select from
More females, more records
If you test more males, is there more or less to select from? What does having more males mean for females?
More to select from
Less females, less records
When there are fewer males, what happens to intensity and accuracy?
i decreases and acc increases
When there are more males, what happens to intensity and accuracy?
i increases and acc decreases
What is replacement rate?
Rate at which newly selected individuals replace existing parents in a population
If intensity increases, what happens to generation interval?
It increases (and vice versa)
What is the normal rule for females?
i increases, L increases
What is the rule used when deciding if females should be saved?
If sires are genetically far superior to dams, there are many replacement females
If sires are slightly better, there are fewer replacements and you can be more selective
What is selection risk?
Risk that the true breeding values of replacements will be significantly poorer than expected
What is selection risk like for males?
Fewer sires, more intensity, more risk
What is selection risk like for females?
Not an issue
Why is the selection of males more important than females?
More progeny
Higher accuracies
Up to 90% of genetic change can be attributed
What does the rate of genetic change depend on?
Accuracy of selection or accuracy of BV predictions
What is the accuracy of selection increased by?
Increasing h^2 Managing animals uniformly Taking careful measurements Adjusting for known environment Use of contemporary groups
How do you increase accuracy of selection further?
Use as much info as possible
Weigh each piece of info appropriately
What is selection index a method of?
Genetic prediction
What is the equation for selection index?
I = b_n x x_n
What are 3 sources that information used in calculating genetic prediction for an individual comes from?
Individual’s own performance
Performance records of ancestors
Performance record of descendants
What data is used in selection index?
Individual’s own performance for trait
Individual’s paternal half sib average performance for a trait
Individual’s average progeny performance for a trait
Performance of individual, half sib, and progeny for correlated trait
How is phenotypic info usually expressed?
As a deviation from contemporary group mean
Why should old contemporary groups not be used?
Because of updates
What is the equation for a prediction using a single source of information?
I = bx
What is common among half sibs?
Paternal environment
What is common among full sibs?
Maternal environment
What are 3 factors affecting accuracy of prediction?
h^2
Pedigree relationship
# of records
What are half sib records a good indicator of?
Sire
What do half sib records not determine?
BV of progeny
How do you calculate a prediction for multiple sources of information?
I = b1x1 + b2x2 + b3x3…..
What are pedigree estimates?
Prediction based solely on pedigree data
What is BLUP?
Best linear unbiased prediction
What does BLUP calculate?
Solutions simultaneously of a number of equations for an entire population of animals
Why is BLUP a preferred method?
Large scale evaluation
Typically entire breeds
Field data taken by producers
What are the types of statistical models in BLUP?
Sire
Maternal grandsire
Animal models
What are animal models?
Most popular
Evaluates all animals instead of certain ones
What does BLUP account for? (6)
Differences in the mean breeding values of contemporary groups
Genetic trends
Info from all individuals in population
Non-random mating
Culling due to performance
Direct and maternal components of a trait
What are direct components of a trait?
Effect of an individual’s genes on the performance
What are maternal components of a trait?
Environment provided by the dam
What are maternal components affected by?
Genes of the dam
What can BLUP predict?
EBV's EPD's MPPA's Total maternal value BLUE Any animal in population
What is BLUE?
Best linear unbiased estimators
What is an example of BLUE?
Sex effects
Management
Environment
What is done before BLUP in large populations?
Central tests
What are central tests?
Comparing animal from different herds or flocks
What are factors of central tests?
Only a few traits
Animal performance only
Location preference
When was BLUP first used?
1980s
What did early information from BLUP do?
Designed tests
What does BLUP do now?
Field data reported to breed associations or other agencies for evaluation
Why is it called a sire summary?
Because males have more progeny
What are direct components’ performance attributed to?
Genes inherited from the sire
What is total maternal?
Combination of direct and maternal
What are accuracy values a measure of?
The relationship between trait values and their prediction
What is the range of accuracy values?
0 to 1
If you expand the pool of available sires, what happens to selection intensity?
Increases
If Bull A’s EPD is +10 for weaning weight and bull B’s EPD is -5 for weaning weight, what do you expect for the progeny?
We expect Bull A’s progeny to weigh 15 pounds heavier on average than Bull B’s progeny at weaning when mated to similar females
What does an EPD of zero represent?
The breed average for the trait in a specific year
When there is high accuracy, how much selection risk is there?
Little
When there is low accuracy, how much selection risk is there?
High
What does accuracy tell about?
Reliability of EPD
What are some faulty data examples on pedigrees?
Parental misidentification
What are some faulty data examples on performance records?
Falsifying records
Incomplete reporting
What are some faulty data examples on adjustment?
Wrong information about known environmental effects
What are some faulty data examples on contemporary groups?
Reported as members of the wrong group
Treatment differences
What are some faulty data examples on relationship among groups?
Individuals related in different groups
AI increases connectedness
What are some faulty data examples on G x E interactions?
Significant interaction can cause problems
Low heritability traits are more susceptible
