Genetics and Sire Selection

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Genetics and Sire Selection
Dr. Darrh Bullock Dr. Jack McAllister Introdu
ction to Animal and Food Sciences Agent In-Service
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GENETICS The science of how biological informatio
n is transmitted from one generation to the next
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GENES CONTROL EVERYTHING
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CONCEPT OF GENETIC MERIT
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Basic Genetics
Trait Genetics Environment
Phenotype Genetic Environment
Potential Influences
P G E

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DETERMINATION OF GENETIC MERIT
G IS ESTIMATED FROM P WITH ADJUSTMENTS FOR E
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GENETIC LIKENESS

• Additive genetic relationship
• Inbreeding

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CAPITALIZING ON GENETIC MERIT
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Genetic Effects

• Additive Genetics
• Non-additive Genetics

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Additive Genetics

• These are the genetic effects that get passed
  from one generation to the next.
  
• This is each genes influence independent of
  other genes and the environment.

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Additive Genetics

• It is the independent effect of all of the genes
  that influence a trait added together.
  
• Heritability is the proportion of the total
  variability that a trait has that is attributed
  to additive genetics.

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TYPICAL HERITABILITY ESTIMATES - LOW
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TYPICAL HERITABILITY ESTIMATES - MEDIUM
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TYPICAL HERITABILITY ESTIMATES - HIGH
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Selection

• Additive genetic effects are the basis of
  selection.
  
• Whether natural or artificial the intent is to
  concentrate superior genes in the next generation.

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Selection

• In highly heritable traits this is easily and
  rapidly accomplished.
  
• In lowly heritable traits it takes many
  generations to make any progress and other
  factors still play a large role.

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Selection

• Selection can occur both within herd/flock and by
  importing genetics (AI, service sires,
  replacement females).
  
• Goal is to increase the proportion of desirable
  genes.

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Non-additive Genetics

• There are a group of genetic effects that are not
  independent of other effects
  
• This group of genetic effects which influences a
  trait cannot be simply added together and thus
  the entire group is referred to as non-additive
  genetic effects.

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Non-additive Genetics

• These include such effects as dominance, genetic
  and environmental interactions.

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Non-additive Genetics

• These genetic effects are in response to how
  genes influence each other at certain loci
  (dominance), environmental influences or what
  genes are located at other loci.
• Heterosis is an example of non-additive genetic
  effects.

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Crossbreeding

• Non additive genetics are the basis of
  crossbreeding because it allows us to take
  advantage of dominance.
  
• Crossbreeding creates greater heterozygosity in
  the offspring.
  

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Crossbreeding

• The dominant trait is often the favored trait and
  therefore instead of the offspring being the
  average of the parents it often performs similar
  to the parent with the favored trait.
• The term for this effect is heterosis.

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WHAT IS HETEROSIS

• The advantage a crossbred has over the average of
  the breeds represented in the cross

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HETEROSIS
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TYPICAL HIGH HETEROSIS
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TYPICAL MODERATE HETEROSIS
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TYPICAL LOW HETEROSIS
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Breed Complementarity

• Selecting breeds that have characteristics that
  are compatible with the management system.
  
• Selecting breeds that complement each other.

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Crossbreeding Systems

• Maintain high heterosis
• Utilize breed complementarity

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Crossbreeding Calculator
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Economics of Heterosis- An Example in Beef

• 30 head herd
• 85 Weaned/Cow Exposed
• 525 lb Wean Wt.
• 85/cwt

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Herd Economics of Heterosis
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Herd Economics of Heterosis
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Herd Economics of Heterosis
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Herd Economics of Heterosis
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Herd Economics of Heterosis
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Selection and/or Crossbreeding
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Selection of Breeding Stock

• Sires
• Replacement Females
• Culling

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Sire Selection

• Reproductive Soundness
• Structural Soundness
• Performance
• Visual Appraisal

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Visual Appraisal

• Disposition
• Structure
• Feet and Legs
• Shoulder and Hip
• Top-line
• Type

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Visual Appraisal

• Body Capacity
• Muscling (Beef, Sheep, Swine and Broilers)
• Udder (Dairy, Swine and Beef?)
• Other Factors
• Horns
• Color
• Comb
• Etc.

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BODY CAPACITY
UDDER
MUSCLING
OTHER FACTORS
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Performance

• Actual Measurements (P)
• Contemporary Group Ratios or Deviations
• Breeding Values (BV)

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Actual Measurements

• Not very useful when trying to determine how good
  an animals offspring will be because environment
  has a large influence on actual measurements.
  
• Advantageous management often masks poor genetics.

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Contemporary Group Ratios

• Calculated by dividing the average of all animals
  of the same sex raised together, under similar
  conditions, into each animals measurement.
  
• Average animal ratio of 100. A ratio of 114
  means the animal was heavier/larger than the
  average by 14.
  
• Still not a very good predictor of how a animals
  offspring will perform. Half the offspring in
  the worst herd in the country will ratio over
  100.

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Breeding Values

• A prediction of the genetics a parent will pass
  on to their offspring, when compared to other
  animals.
  
• Take into account the actual measurement on the
  animal, all relatives measurements and
  environment.

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Breeding Values

• Not a perfect science, so use as risk management
  tool.

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TERMS FOR ESTIMATION OF GENETIC MERIT

• BV breeding value
• EPD expected progeny difference
• PTA predicted transmitting ability (dairy)

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EPD PTA ½ BREEDING VALUE
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EPD
5.1 lbs
2.2 lbs
Expect the average difference in
offspring to be 2.9 pounds.

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EXAMPLES OF EPDS/PTAS
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GENETIC RELATIONSHIPS ARE KEY TO GENETIC
EVALUATIONS
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COMMON GENETIC RELATIONSHIPS
Additive
Relatives
Genetic
Relationship
Parent - offspring(O) .50
Grandparent(GP) - O .25
Great-GP - O
.125 Half bros. sisters
.25 Full bros. sisters
.50 First cousins
.125 Aunt/Uncle - Neice/Nephew .125
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GENETIC INDEX Genetic merit for individual
traits weighted by their economic contribution
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Dairy Lifetime Net Merit

• Net Merit (NM) Yield Udder Other
• Yield (MFP - FEED ) No. Lactations
  Actual Yield

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NON-GENETIC INDEXES (PHENOTYPIC INDEXES)

• Average Earnings Index (other thoroughbred
  indexes)
  
• Production Type Index (PTI) - Jersey
• Type Production Index (TPI) - Holstein

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Jersey PTI

• PTI (8 x PTAP) (2 x PTAF) (2 x FTI)
• (2 x PTAPL) (1 x PTASCS)
• PProtein, FFat, FTIFunctional Type
• Index, PLProductive Life, SCS Somatic
• Cell Score

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HOLSTEIN TPI

• PTAT PTA for type
• TPI 36 x w1x PTAP 18 x w2 x PTAF 15 x
  w3 x PTAT 10 x w4 x UDC
  
• 5 x w5 x FLC 11 x w6 x PL
• -5 x w7 x SCS/.13 1241
• UDCudder composite, FLCfeet leg
• composite

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OTHER GENETIC ISSUES

• Single gene traits
• Dominance
• Recessive traits
• Inbreeding
• Molecular avenues

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SINGLE GENE TRAITS

• Hyperkalemic Periodic Paralysis (HYPP)
• Muscular disease in horses and humans
• Causes uncontrolled muscle twitching and
  weakness in severe cases can cause sudden
  collapse and even death
  
• Inherited as an autosomal dominant trait

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GAMETES AND PROGENY PRODUCED BY MATING
HETEROZYGOUS HYPP MALE AND FEMALE
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Recessive Traits

• Identifiable only as homozygotes (i.e. both genes
  in a pair of genes are recessive)
  
• Even if lethal, reducing the frequency takes a
  long time
  
• If frequency is .5 in the population to begin
  with and recessive gene is lethal, it will take
  about 8 generations to reduce the gene frequency
  to .1

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OTHER TRAITS
Coat color Horns
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INBREEDING/LINEBREEDING

• Inbreeding the mating of related individuals
  which increases the likelihood that genes at a
  given site on the chromosomes (locus) are
  identical by descent indiscriminant with regard
  to whether genes are good or bad
• Linebreeding repeated matings back to a common
  ancestor over generations a mild form of
  inbreeding

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Molecular Technology

• Parentage
• Marker Assisted Selection
• Single Gene Traits
• Horned/Polled
• Red/Black
• Genetic Defects

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Molecular Technology

• Marker Assisted Selection
• Multiple Gene Traits
• Marbling
• Tenderness
• Milk Production
• Reproduction
• Other Production Traits

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Uses for Molecular Technology

• Direct Selection
• Single Gene Traits

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Uses for Molecular Technology

• Direct Selection
• Single Gene Traits
• Multiple Gene Traits

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Slide courtesy of Jay Hetzel
A simple result
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NBCEC vs. Genetic SolutionsMarbling Score Results
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NBCEC vs Genetic Solutions Choice Results
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Should producers be buying bulls with Genestar
Marbling?

• Not so fast
• Depends
• Maybe

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Example

• Bull A is a 2 star for marbling and has a
  Marbling EPD of 1.0
  
• Bull B is a 0 star for marbling and has a
  Marbling EPD of 2.0
  
• Which bull should you use to increase marbling?

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Marbling EPDs
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Interpreting Test Results

• The most logical and useful way to report test
  results is to include tests in EPD calculation
  
• Direct gene and/or marker tests can be included
  in National Genetic Evaluation programs