Sheep genetics lec 1 Flashcards Preview

ASC 370 > Sheep genetics lec 1 > Flashcards

Flashcards in Sheep genetics lec 1 Deck (27):

• 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

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

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?


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)