Flashcards in AB&G - Mid-semester exam revision Deck (18)
List the 5 steps in developing a breeding program
Define the breeding objective
Choose selection criteria
Organise performance recording service
Use of performance information for making selection decisions
Use selected animals
List the 4 steps in developing a breeding objective (the 1st step in developing a breeding program)
Specify the breeding, production, and marketing system
Identify sources of income and expense in commercial herds/flocks
Determine biological traits influencing income and expense
Derive economic value for each trait
How do you calculate the generation interval?
Lf = (# 1y.o females * 1)+(# 2y.o females * 2)+(# 3y.o females * 3).../total number of females
Lm = (# 1y.o males * 1)+(# 2y.o males * 2)+(# 3y.o males * 3).../ total number of males
What units is the generation interval in?
What is the equation for effective population?
How do you calculate selection intensity?
First, calculate the proportion of the progeny born each year required as replacements (for each sex), Pf and Pm.
Find the corresponding selection intensity from the table provided
Average the selection intensities from each sex
Explain what the selection intensity represents
It's the SD of the means of the selected individuals vs the entire population
What is the equation for the change in inbreeding coefficient per generation?
Delta F = 1/(2*Ne)
How do you calculate the response to selection?
R=(variation*selection intensity*accuracy)/generation interval
Explain the equation for the correlated response in trait 2 when selecting for trait 1
CR=genetic correlation * selection intensity * heritability of trait 1 * heritability of trait 2 * phenotypic variation (SD) in trait 2 / generation interval
Why might you select indirectly?
Because some direct traits are
- difficult/expensive to measure
- only expressed in one sex
- only expressed later in life
- lowly heritable
- only expressed in certain environments/conditions
What makes good indirect traits?
- Cheap/easier to measure than direct traits
- expressed in both sexes
- expressed early in life
- expressed in all environments/conditions
- have higher heritability than direct traits
- have large variation
- good genetic correlation with direct traits
What is the equation for the direct response to selection for trait 1?
R1 = phenotypic variation (trait 1) * selection intensity * heritability (trait 1)
When is indirect selection better than direct?
When the correlated response is greater than the direct response.
When CR(1,2)/R(1) = genetic correlation (rG(1,2)) * heritability (trait 2) / heritability (trait 1) > 1
What are three methods of selecting for more than one trait?
- selecting for one trait at a time, ignoring all others
- order traits according to importance, then make selections based on the most important trait for a number of generations.
- Then the next most important trait becomes the basis of selection for a few more generations, and so on.
- ADV: Can make maximum genetic improvement in 1 trait
- DISADV: Only selecting for 1 trait at a time
- A fraction of animals are selected for each trait (alone)
- For trait 1, a fraction p(1) is selection; trait 2, p(2); trait m, p(m); etc.
- The total fraction selected is the product of the fractions selected for each trait: p = p(1) * p(2) * p(m).
- p is usually determined by the breeding requirements.
- ADV: culling can follow the biological development of the animal (e.g. culling at weaning, yearling, etc)
- DISADV: Difficult to estimate response to selection and how much pressure to put on each trait.
- Selection based on total economic value
- Combines information on many traits into an index and animals are ranked on the index.
-ADV: captures the economic values of all traits so animals can be selected on their entire economic value.
Define the term economic value and outline the steps to calculate it
The economic value is the monetary value of each economic trait, taking into account the income it generated, the costs involved, and the number of times it is expressed.
Economic value = (income - costs)*# expressions
Describe what is meant by the "desired gains approach" and when it is useful
You identify the genetic gain you desire to achieve over time, and work out the economic values to achieve that (essentially decide on the selection pressure for each trait regardless of their 'true' economic value in).
Useful when there are traits that don't have much (or any) economic value currently/traditionally; e.g. retail yield or tenderness in dairy breeds.