Genetic Control of Cell Function Impact of Selection

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Genetic Control of Cell Function Impact of
Selection?

• Have we been successful in producing different
  products by selection?
• Turkeys breast size for white meat
  reproduction?
• Miniature vs. Tennessee Walkers vs. Draft Horses
  same origin?
• Swine type see pictures at top of page 445,
  original emphasis on lard now on muscle.

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Genetics basic principles of inheritance

• Locus (pl. loci) - the location of a gene in a
  chromosome
• Homologous chromosomes (1 from each parent) -each
  contain a copy of a gene affecting a trait
• Alleles forms of a gene at corresponding loci
  in homologous chromosomes different alleles
  affect the same trait in different ways

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Genetics basic principles of inheritance

• Swine coat color example
• homozygous genes are alike in how they affect
  the trait (2 BLACK alleles)
• heterozygous genes differ in how they affect
  the trait (1 RED 1 BLACK)

BLACK
BLACK
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• MEIOSIS
• production of gametes (oogenesis
  spermatogenesis)
• reduce number of chromosomes
• 1 parent diploid cell to 4 daughter haploid cells
  in sperm
• 1 parent diploid to 1 daughter haploid and 3
  polar bodies in oocytes

Figure 86  Meiosis.
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Allelic Interactions Dominance

• dominant gene overpowers and prevents
  expression of its recessive allele when
  heterozygous for a trait
• recessive gene a gene which is masked by its
  dominant allele when heterozygous for a trait

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Figure 87  The behavior of simple dominant and
recessive traits.
Allelic Interactions Dominance
What Genotypes would result from Rr X Rr?
Phenotype Black Black Red
25 RR 50 Rr 25 rr
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(Codominance)
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(Assumes each gene on a different chromosome)
Table not in text!
How has any uniformity of animals been achieved?
Degree of progress depends upon the nature of the
trait!!!
How many genes affect a given trait?
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Genetics types of traits

• Qualitative
• descriptive subjective measure
• classification into a few distinct groups
• examples hair color horns/polled blood types
• few genes control (often only 1 pair)
• environment has little if any influence
• progress not too difficult with 1 gene
• economic importance??

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Famous Detrimental Recessive Single Genes

• Can have devastating economic impacts!!
• Classical Examples
• Dwarfism in Hereford Cattle
• Spider Lambs
• Mule Foot
• Often start with a popular sire with mutation

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Why is recessive so much more devastating than if
dominant?
Is risk greater with AI?
Not only is 1680 an insanely popular sire amongst
the Angus breed, his sons and daughters are as
well.  Just try finding semen from his highly
popular son CA Future Direction 5321.  GAR
Integrity is no slouch either.  Just take a look
at our profile of GAR Precision 1680 to see just
how many AI sires he has sired and even more
impressively how many AI sires his daughters have
mothered. All of these things seem like they're
bigger than they really are at this point but
there really aren't too many Angus bulls in
existence with more impact than 1680 has had on
the breed.
Has animal science research in molecular genetics
made recessive detrimental genes less of a
problem?
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IGENITY Introduces Curly Calf Syndrome Analysis
In addition to the analysis for AM, the
comprehensive IGENITY profile includes multiple
marker analyses for
IGENITY also offers an optional diagnostic test
for persistent infections (PI) of the bovine
viral diarrhea (BVD) virus.
Human Applications risks?
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Genetics types of traits

• Quantitative much greater economic importance!!
• objectively numerically measured
• continuous variation (unlimited of
  observations)
• many genes control (50, 100, or more pairs)
• examples milk production racing speed weight
  rib eye area

RACING SPEED
LOIN EYE AREA
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Quantitative Trait Example

• Growth Rate of an Animal what controls this?
• appetite, amount consumed, digestion,
  utilization, conversion
• best animal gets best allele for all genes that
  control these!
• influenced by environment?
• -are weight differences among animals due solely
  to genes?
• accuracy of measurement for qualitative vs
  quantitative?
• Gene mapping select on alleles, not on what
  they weigh!

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Genetics

• genotype genetic makeup of an animal
• phenotype characteristics of an animal that can
  be seen or measured (color, weight, speed)
• environment all non-genetic influences that
  affect animal traits (nutrition, season, age,
  health)

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Genetic change through selection

• Selection
• is creating different reproductive rates among
  animals (we want more offspring out of selected
  animals than others)
• increases frequency of desirable genes in the
  population (to increase growth rate, milk
  production, speed, etc.)
• Selection traditionally is performed on Phenotype
  Quantitative Genetics

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Factors affecting rate of genetic improvement
when selecting for quantitative traits

• Heritability of the trait
• Selection differential
• Generation interval

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Heritability
IS temperament heritable or is it a function of
environment?

• heritability for quantitative traits, the of
  phenotypic variation among animals for a
  particular trait that is due to heredity (not
  environment)

GREATER HERITABILITY GREATER IMPROVEMENT
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Selection Differential

• Selection differential
• superiority of selected animals compared to the
  herd average for a particular trait
• Example
• average of selected mares 62 inches
• average of all mares in herd 58 inches
• selection differential ??? inches

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Generation Interval

• average age of the parents when offspring are
  born
• (average age of breeding females average age
  of breeding males) / 2

swine 2 years horses 5-8 years dairy 3-4
years poultry 8-12 months beef 5-6
years sheep 3 years
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Genetic change per year

• heritability x selection differential

generation interval
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Mating Systems

• Designed to either
• Increase homozygosity - increase predictability
  of progeny as future breeding animals.
• Increase heterozygosity - increase performance of
  progeny produced for marketing or production.

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Mating Systems

• Inbreeding
• Intensive inbreeding - close relatives
• brother x sister, many generations
• widely used poultry industry
• e.g.inbred male/female lines for broilers
• increases homozygosity of gene pairs
• tests for undesirable recessive genes
• depresses performance
• increases predictability
• Linebreeding or Inbreeding in other species

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Animal Mating Systems

• 2. Crossbreeding
• mating animals of different breeds or lines
• beef, sheep, swine, dairy?
• Advantages
• breed complementation utilize different breeds
  with strength in traits of interest

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Animal Mating Systems

• 2. Crossbreeding (cont.)
• Advantages
• heterosis aka. hybrid vigor
• increased productivity of crossbred progeny
  above average of breeds or lines that are crossed
• greatest for lowly heritable traits

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Mating Systems

• Why does increased heterozygosity increase
  performance?
• Fewer unfavorable recessive genes expressed
• Favorable dominant genes are combined
• Heterosis or Hybrid Vigor same thing
• Immediate Response

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Tools for Effective Animal Selection

• Expected Progeny Difference (EPD) Beef Cattle
• expected performance of future offspring of an
  animal compared to the average of a group
• calculated from performance of relatives
  ancestors, siblings, progeny
• Traits
• GROWTH birth, weaning weight
• CARCASS rib eye area, fat thickness, marbling
• MILK PRODUCTION

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Tools for Effective Animal Selection

• Dairy Predicted Transmitting Ability (PTA)
• analogous to an EPD
• Milk, Protein, Fat, Cheese
• Somatic Cell Score, Productive Life
• Udder Structure, Teat Structure
• Swine
• Number born alive, 21 day litter weight
• backfat depth, days to 230 pounds
• Selection indexes for maternal or growth

SELECT SIRES, INC.
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Genetic Improvement
selection plus crossbreeding
selection, no crossbreeding
Level of Performance
crossbreeding, no selection
no selection, no crossbreeding
TIME