Sheep genetics lec 1

Question 1

• Understand why the rate of genetic progress in the wool industry has been relatively slow

Answer 1

-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

Question 2

define selection

Answer 2

choice of breeding stock to generate genetic change in the flock

Question 3

define breeding objective and what is its aim

Answer 3

sets direction of enterprise, traits given economic weight to indicate desrirability

animals assigned a rank

improve profitability

Question 4

what does BLUP stand for and when is it used?

Answer 4

best linear unbiased predicion

used to help make estimations of random effects

most accurate measure if BV from phenotype

Question 5

what has been the overal genetic trends?

Answer 5

dairy- inceasing
wool- fairly stable
lamb- increased in recent years

Question 6

define selection theory

Answer 6

makes use of known relationships between traits

allows for other cheaper traits to be measured

Question 7

how do you increase profibaility in the sheep industry (3)?

Answer 7

increase economic return by generating better qaulity prodcuts

increase efficiency

reduce input costs

Question 8

what is the measure of phenotype?

Answer 8

phenotype = genotype + enviroment

deviation from flock average

stringer emphasis on genotype

Question 9

define heritability

Answer 9

(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

Question 10

define repeatability

Answer 10

extent to which superiority in one year is maintained in the next

rank
values between 0 and 1

Question 11

what is a trait with high and low repeatability?

Answer 11

high- body weight

low- repro rate

Question 12

what is a trait with high and low heritability?

Answer 12

high- live weight

low- weaning %

Question 13

define selection differential

Answer 13

superiority of selected animal over average

Question 14

what is EBV and give an example

Answer 14

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

Question 15

what is a generation interval (L) and how is it calculated?

Answer 15

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

Question 16

what is genetic correlation?

Answer 16

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

Question 17

what is the advantage and disadvantages of a short generation interval?

Answer 17

+ quicker response to selection
+ younger animals superior

• less superior animals selected

Question 18

what is an exmple of high and low genetic correlation?

Answer 18

high- CFW and GFW

low- CFW and fold score

Question 19

what is the key thing to remeber in EBVs?

Answer 19

half as the animal can only contribute 1/2 of the genetics

if EBV for one parent is unknown, assume it is 0

Question 20

main advantage of BLUP?

Answer 20

can use info from different flocks and averaged within years

Question 21

what is the advantage of using genetic correlation?

Answer 21

can use other traits to estimate superirority in another trait

Question 22

what is a selection index?

Answer 22

rank

number of traits selected simultatneously based on REV and EBV

Question 23

what is the current breeding structure of the merino industry and what is the disadvantage of this?

Answer 23

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)

Question 24

What is the open nucleus structure?

Answer 24

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

Question 25

what is the response to selecting a ram/ewe?

Answer 25

= h2 x selection diff (rams or ewes)/2

Question 26

what is the total reponse per generation?

Answer 26

= h2 x average selection diff

Question 27

what is the equation for response?

Answer 27

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)
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