Responce to selection

Question 1

is our “selection system” leading to genetic progress

Answer 1

depends on:
-generation interval (L)
-selection intensity (i)
-variation in population (selection differential)
-h2 of trait
-accuracy of selection
-effective population size

Question 2

generation interval (L)

Answer 2

average time (years) between when an animal & its replacement is born

Question 3

what is generation interval affected by

Answer 3

-gestation length
-age of puberty
-like sex replacment

Question 4

what is selection intensity (i)

Answer 4

-average portion of animals selected
-fewer males kept then females
-smaller proportion of litter bearers
-based on proportion of animals kept for breeding
-expressed as STD units of expected progeny improvment

Question 5

what is variation

Answer 5

-selection differentials (sd)
-change in lbs, litter size, etc. of the selected group vs total
-sd = mean of selected-mean of total
e.g. ADG =3lbs/day-2.4lbs/day = 0.6 lbs/day

Question 6

accuracy of selection

Answer 6

-ranges from 0 to 1 depends on:
-1) method of selection i.e. individual, ancestor
-2) number of measurements
-3) heritability h2=accuracy

Question 7

effective population size (Ne)

Answer 7

-must be large enough to avoid inbreeding and to maintain variation for selection
-Ne= 4 (sires)(dams)(L)/ sires+dams
-for inbreeding to be <1%
Ne greater or = 50/L of female

Question 8

genetic gain

Answer 8

-genetic improvement over time
-delta G=(rA,A)(ip)(s.d.A)
delta G=genetic gain
r A,A = accuracy of selection
ip= selection intensity factor
-s.d.A= standard dev (additive genetic)

Question 9

genetic gain per year

Answer 9

-delta g= delta G/L
-genetic gain/yr = genetic gain/generation interval

Question 10

how to increase genetic gain/yr

Answer 10

-inc selection intensity (select fewer)
-inc accuracy of selection (use individual selection, rater then pedigree)
-inc genetic variation (introduce new quality stock)
-decrease generation intervals

Question 11

what is velogenetics

Answer 11

-not that common
-harvest embryos form 6mo old heifer

Question 12

what are some strategies to measure genetic progress

Answer 12

1) measure to contemporaries
-doesn’t really measure improvements
-does assess “position” in industry
2) improvement over time
-compare offsprings performance to parents
-compare herds performance over many years
3) repeat mating design

Question 13

how can you repeat mating design to measure genetic progress

Answer 13

a) compare new bull to old bull
-breed young females with semen from old bull
-breed young females with semen form new bull
-since env are same diff is prob genetic
b) transplant stored embryos and fresh embryos in one season
-compare performance of calves (both male and female genetics studied here)

Question 14

how do you know if you dont have genetic progress

Answer 14

-hit a plateau
-genetic progress is offten “uniformity”
-the desired trait is now fixed

Question 15

why sometimes can you achieve more genetic progress but its actually not beneficial

Answer 15

-negatively correlated responses thwarting progress
-ie. can inc growth with out serious fertility problems
-can inc pig ADG with out inc feed costs

Question 16

what are some solutions to no genetic progress

Answer 16

a) cross 2 plateaued strains to introduce variation
b) expose latent variation (alter day length in barn, improve diet)
-re evaluate goals (add disease resistance)