Selection Flashcards
What is the most effective means to influence rate of genetic change?
selection
How does selection result in genetic change?
alters genetic frequency
How do mating systems result in genetic change?
genotypic frequency change
How can animals within a population appear different?
within a population there is huge variation in types of alleles and how they combine
What happens to the mean of a population as you select for best traits?
shifts the mean
What does rate of genetic selection depend on?
- heritability
- selection differential
- population size
- generation interval
How does heritability affect rate of genetic selection?
higher heritability results in faster rate of change
What happens if a trait is lowly heritable?
they don’t respond as fast to selection
What is selection differential?
the mean value of selected individuals subtracted by the mean value of population from which they were selected
How does population size affect rate if genetic seleciton?
a greater population size results in greater superiority
What is generational interval?
- average age of parents when the offspring are born
- average number of years for turnover of a population
Is a longer or shorter generational interval better?
shorter
What are the sources of information for basis of selection?
- individual performance
- pedigree-ancestors
- collateral relatives
- progeny
What is the purpose of the basis of selection?
to judge which animal is best
What are examples of individual performance?
weight, feed efficiency, milk data, etc
What is a problem with individual performance?
has limitations
What is pedigree?
information based on ancestor performance (tells who is the sire, dam, and cousins of individual)
Where do you get pedigree information?
is provided to you
What is collateral relatives?
half or full siblings
What does progeny measure?
the genetic worth of animal by looking at offspring
Until you can evaluate the offspring…
you cannot fully evaluate the animal
What is the best source of information for selection?
progeny
What is accuracy of selection a measure of?
the relationship between the true breeding values and the predicted breeding values
The more accurately we predict breeding values…
the greater the probability that the animals we choose to be parents will be the best parents
What is the most important parameter you can measure?
breeding value
What is the formula for accuracy of selection?
ACC=square root (H^2)
What does the accuracy of selection depend on?
- heritability
- number of records
- adjusting for environmental factors
- contemporary groups
- careful measurement
What records are being looked at?
progeny and other relatives
Are more or less records better for accuracy?
more
How do you adjust for environmental factors?
make sure things that can influence performance are accounted for so you only are measuring potential of the animal and not the environment
What do you do with contemporary groups?
compare animals born at the same time and kept within the same environment
What does it mean to take careful measurements?
take measurements in the same point across the animal
What is the accuracy of selection in simple terms?
the relative reliability of estimate
What is the accuracy of selection statistically?
estimate of how accurately the genotype of the individual for a certain trait can be predicted from the phenotypic averages of it’s relatives
What does the accuracy of selection not suggest?
genetic net worth of an animal
Is accuracy of estimate permanent or will it change over time?
will change over time
How is accuracy of selection affected by progeny (in terms of graph)?
as you have more progeny, the accuracy increases and eventually plateaus
How is accuracy of selection affected by half sibs (in terms of graph)?
not as good as full sibs
How is accuracy of selection affected by full sibs (in terms of graph)?
higher accuracy in full sib compared to half because have both same parents
What is selection intensity?
a measurement of how “choosy” breeders are in deciding what animals will become parents
What does high selection intensity mean?
choose only the very best individuals
Parents selected with high intensity should be _____ than the average.
much better
What is the only way to determine the actual genetic worth of an individual?
progeny test
In what direction does the mean shift?
depends on the trait
How many traits does estimated breeding value measure
one
What is the formula for expected breeding value?
h^2 ( x - x (line above)) / 2
In EBV, what does x represent?
individual performance
In EBV, what does x (with line above) represent?
mean contemporary group
What is the formula for selection differential?
x - x (line over it)
Why is EBV divided by 2 in the formula?
half of genetic potential from animal x
In average herd, animal being bred by ___ is average?
X
What is the formula for EPD (expected progeny difference)?
EBV + X (with line over it)
Will EPD value change?
it should change little as it is affected by the bull’s genetics
How do you measure the progress/year?
EBV / GI
Is Generation Interval calculated separately for males and females?
yes
What is L?
the weighted average of males and females
How is there generation interval within a population?
different number of males and females and breed at different ages
What is the time it takes to replace all the parents with offspring?
average age of the breeding herd when their selected offspring are born
What is the most commonly used source of selection information?
individual performance
What is the value of individual performance highly related to?
heritability
What are examples of highly heritable traits?
growth traits, carcass traits, wool traits
What are some growth traits?
- birth weight
- average daily gains
- yearling weight
What are some carcass traits?
intramuscular fat,
What are some wool traits?
staple length
What are disadvantages of individual performance (list)?
- sex-limited traits
- traits requiring long time
- carcass traits
- low heritable traits
Why are low heritable traits a disadvantage of individual performance?
low accuracy
What are types of traits are lowly heritable traits?
reproductive/fertility traits
What are some reproductive/fertility traits?
yearling pregnancy, breeding rate, days open, first service conception, calving ease
What is first service conception?
getting pregnant at 1st service (at first breeding)
What are lowly heritable traits (definition)?
environment has more effect that genetic
heritability formula?
genetic variance / phenotypic variance
What affects pedigree?
- degree of relationship
- heritability of trait
- environmental correlation between ancestor and individual
- how well trait was measured
What is the degree of relationship to parents?
1/2
What is the degree of relationship to grandparents?
1/4
What is the degree of relationship to great-grandparents?
1/8
How does environmental correlation b/n ancestor and individual affect pedigree?
if ancestor was under a better or worse environment it can affect performance
What are advantages of pedigree?
- cheap
- valuable for sex-limited traits
- valuable for traits expressed later in life
- low heritable traits
How is pedigree cheap?
data is cheap and online
How is pedigree valuable for sex-limited traits?
can see the female on both sides
How is pedigree valuable for traits expressed later in life?
see how generationally a trait has been performed
What are the disadvantages of pedigree?
- lack of accurate records/environmental influences of ancestors performance records
- provides no comparative basis for selection among individuals that are all descendants of the same ancestor
What does full sibs mean?
same parents
What does half sibs mean?
one parent in common
What is the value of collateral relatives?
- sex-limited traits
- traits that require slaughter to measure
- accuracy tends to be lower than individual performance except for lowly heritable traits
Why don’t lowly heritable traits have lower accuracy for collateral relatives than individual performance?
because of increased number of observations
What affects the accuracy of a sib test?
- heritability of trait
- relationship of sib (closeness)
- number of sibs tested
- correlation between phenotypes of sibs
If you use the correlation between phenotypes of sibs, what should you make sure is true?
- environmental correlation is high
- full sibs have maternal environment from conception to weaning
How related are full sibs?
1/2 related
How related are half sibs?
1/4 related
If you are interested in determining the genetic worth of an animal what do you do?
progeny test
What is progeny testing?
evaluation of the genetic makeup of an individual by phenotype of it’s progeny
What are the 2 traits can progeny tests be performed for?
- qualitative traits
- quantitative traits
What is the major objective of progeny testing for qualitative traits?
help determine the likelihood that an animal is a carrier of detrimental recessive allele
What is an example of a disorder caused by detrimental recessive allele?
CID or SCID
What does CID stand for?
combined immunodeficiency
How is CID carried genetically?
autosomal recessive
What does autosomal recessive mean?
need 2 recessive alleles to show the trait
What does CID cause?
decreased immunity due to defect in a gene, susceptible to infection as maternal immunity wanes
What animal does CID happen in?
Arabian horses
Is CID lethal? When do they die?
yes; around 2 months
How do animals normally fight infection?
get immunity built up from colostrum from mother
What diseases are horses with CID susceptible to?
pneumonia
Why do animals with CID die around 2 months?
immunoglobulin level decreases to a point where they cannot do anything
What gene is defected that results in CID?
DNA-PKcs
What does DNA-PKcs stand for?
DNA protein kinase catalytic subunit
What amino acids are phosphylated?
tyrosine, threonine, and serine
What happens when Tyrosine, Threonine, and Serine are phosphylated?
enabled them to perform protein folding
What does protein folding allow to happen
Can see resumption of immune system in animal
What factors affect the “success” of progeny test for qualitative traits?
- genetic make-up of animal (genotypes available)
- number of offspring that can be produced
What does the number of offspring required to determine the likelihood an animal isn’t a carrier of a detrimental trait depend on?
type of potential crosses
What are the types of test matings?
- sire x recessive (H_ x hh)
- sire x heterozygote (H_ x Hh)
- sire x daughter (H_ x H_)
What are the advantaged of sire x recessive test mating?
fewer matings required
What are the disadvantages of sire x recessive test mating?
finding recessive animals
What are the advantages of sire x heterozygote test mating?
known carrier
What are the disadvantages of sire x heterozygote test mating?
ID animals, more matings
What are the advantages of sire x daughter test mating?
easier to obtain, test for any recessive
What are the disadvantages of sire x daughter test mating?
inbreeding depression, many progeny required
What is the major objective of progeny testing for quantitative traits?
determine the breeding value of parents
offspring represent ___ BV of parent?
1/2
What is the basis for EPD’s and EPV’s?
offspring are 1/2 BV of parent?
What factors affect the accuracy of progeny test for quantitative traits?
- dams must be random
- offspring tested in same environment
- compare parents of a similar age, environment
- increased number of progeny = increased accuracy
If for accuracy of progeny test on the tables you get above 1, what is that saying?
progeny testing is ___% more accurate than
if got 1.35, then 35% more
as heritability increases, more…
progeny are required to equal accuracy of individual performance
Progeny testing is an excellent tool to predict _____________ when _________.
future parental performance; heritability is low to moderate
What is the net value of animal dependent on?
several traits
Are the traits the net value of an animal depends on equal in economic value?
maybe, may not be (depends on who is picking the trait cow/calf vs feedlot for example)
Are the traits the net value of an animal depends on dependent on one another?
maybe, or they may be independent of one another (which would mean as one trait improves, the other might decline)
What are the three basic methods of selection for more than one trait?
- tandem
- independent culling method
- selection index
What is tandem?
trying to improve one trait at a time (select for one trait, then select for another, then another…)
What are problems with Tandem?
- genetic relationship between traits
- more traits = slower progress
- takes a long time
-milk production vs fat %, if you improve for production and then move to fat, you will lose some produciton
What is independent culling method?
set up minimum standards and the animals must meet this standard before it is selected for breeding purposes. You set up multiple standards, and if an animal fails in just one standards you don’t select it.
What is a problem with independent culling method?
cull animal outstanding in one trait
What requirements must a pig meet in order to be saved for breeding?
- from a litter of 8 weaned
- must weight 180 lb at 5 months of age
- no more than 1.3 inches of backfat at 200 lbs live weight
What is selection index determined?
- place different degrees of emphasis on traits of interest
- make equation to determine genetic worth of animal, based on your objectives
Are traits in selection index’s value determined together or separately?
separate determination of the value for each trait selected for and the addition of these values gives a total score
What is the formula for selection index?
I = b1x1 + b2x2 + …. bnxn
In selection index formula, what is I?
index value
In selection index formula, what is b1?
weighing vector
In selection index formula what is x1?
single item of phenotypic information
What is selection index value?
a single number that predicts the breeding value of an individual for a weighted combination of traits
What does BLUP stand for?
Best Linear Unbiased Prediction
What is BLUP a modification/extension of?
selection index
What does BLUP involve?
simultaneous solution of number of equations using matrix algebra
What is BLUP?
a method of genetic prediction (for selection) particularly appropriate when performance date comes from genetically diverse contemporary groups
What are the keys for selection based on more than one trait?
- genetic relationship among traits
- number of traits selected for
- heritability of traits
What are factors of genetic relationship among traits?
- positive or negative relationship
- how strong relationship is
Is a positive or negative relationship better for selection of more than one trait?
positive (high correlation)
Are more or less traits selected for better for selection of more than one trait?
less because more = slower progress
