Sheep genetics lec 1 Flashcards
• Understand why the rate of genetic progress in the wool industry has been relatively slow
-breeding structure
paper new England uni
- Merino diverse breed, range of breeding objectives
o generation intervals typically longer
o lower level of pedigree recording
o Merino breeders traditionally place more emphasis on subjective traits
define selection
choice of breeding stock to generate genetic change in the flock
define breeding objective and what is its aim
sets direction of enterprise, traits given economic weight to indicate desrirability
animals assigned a rank
improve profitability
what does BLUP stand for and when is it used?
best linear unbiased predicion
used to help make estimations of random effects
most accurate measure if BV from phenotype
what has been the overal genetic trends?
dairy- inceasing
wool- fairly stable
lamb- increased in recent years
define selection theory
makes use of known relationships between traits
allows for other cheaper traits to be measured
how do you increase profibaility in the sheep industry (3)?
increase economic return by generating better qaulity prodcuts
increase efficiency
reduce input costs
what is the measure of phenotype?
phenotype = genotype + enviroment
deviation from flock average
stringer emphasis on genotype
define heritability
(h^2)
degree to which superiority transferred to next generation
indicates how fast a population can be shifted by selection
value between -1 and +1
define repeatability
extent to which superiority in one year is maintained in the next
rank
values between 0 and 1
what is a trait with high and low repeatability?
high- body weight
low- repro rate
what is a trait with high and low heritability?
high- live weight
low- weaning %
define selection differential
superiority of selected animal over average
what is EBV and give an example
estimated breeding value
predcits how a selected animals progeny will perform relative to the rest of the flock
EBV i = h^2 i x predicted superiority
what is a generation interval (L) and how is it calculated?
average parent age when offspring born
determined by the average age of the breeding flock
can calc seperate for males and females, but L is the average of both
what is genetic correlation?
The extent to which two traits are controlled
by the same set of genes
high correlation- increase in 1 trait means increased in trait 2
value between -1 and +1
To what extent will selection of individuals of high performance for trait 1, give rise to progeny of high performance for trait 2
what is the advantage and disadvantages of a short generation interval?
+ quicker response to selection
+ younger animals superior
- less superior animals selected
what is an exmple of high and low genetic correlation?
high- CFW and GFW
low- CFW and fold score
what is the key thing to remeber in EBVs?
half as the animal can only contribute 1/2 of the genetics
if EBV for one parent is unknown, assume it is 0
main advantage of BLUP?
can use info from different flocks and averaged within years
what is the advantage of using genetic correlation?
can use other traits to estimate superirority in another trait
what is a selection index?
rank
number of traits selected simultatneously based on REV and EBV
what is the current breeding structure of the merino industry and what is the disadvantage of this?
pyramid where the stud sector (top) has 2% of ewes and filters to daughter stud then general stud
disadvantage is takes longer for improvements to make its way down into the general population (lag period)
(closed nucleus)
What is the open nucleus structure?
pyramidal, few elite breeding in the upper, large number in a lower
animals from lower down can contribute progeny to the upper tiers
faster rate of change
what is the response to selecting a ram/ewe?
= h2 x selection diff (rams or ewes)/2
what is the total reponse per generation?
= h2 x average selection diff
what is the equation for response?
R= ((intensity male (im) x accuracy male (rm))+intensity male (if) x accuracy female (rf))/ generation interval male (Lm) + generation interval female (Lf)) x genetic SD (oG)
