B65 Animal Genetic

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B65 Animal Genetic
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Lesson Outline

• Introduction
• Phenotype
• Environmental Factors
• Natural Selection
• Controlled breeding
• Two-Breed Cross
• Three Breed Rotation Cross
• Gene Transfer

• Genetic Engineering
• Differentiation
• Alleles
• Gene Dominance
• Punnett Square
• Mendilin Genetics
• Codominate Genes
• Additive Expression of Genes

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Introduction

• No two animals are exactly alike. Even with twins
  one may be taller, one may be heavier, or grow
  faster.
• The two main factors that contribute to these
  differences in animals are
• The environment.
• The genetic make up of the animal.

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Phenotype

• The phenotype is the physical appearance of the
  animal.
• The genotype is the genetic make up of the animal
• Both the environment and the genetic make up
  effect the physical appearance of the animal.

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Environmental Factors

• The quantity and quality of the feed
• Climate conditions
• Exposure to parasites and diseases
• The type of terrain (steep mountains, desserts,
  irrigated pasture)
• The producer has a lot of control over the
  animals environment.
• A producer can also influence, to a lesser
  degree, the genetic make up of an animal.

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Natural Selection

• In nature, genetics are passed on through the
  process of natural selection. The strongest,
  healthiest, most powerful animal generally
  spreads its genetics. Animals that are weak may
  have a poor immune system and are diseased, or
  may have conformation problems. Generally these
  animals do not survive long enough to pass on
  their genetics.

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Controlled Breeding

• A producer crosses two parents based on a desired
  outcome.
• A tough, dominant, alpha male may not be a
  desirable trait for domestic animals.
• Agriculture producers select for traits that have
  economic importance, such as low birth weight,
  growth rate, feed efficiency, mothering ability,
  carcass traits.
• The economically important traits are influenced
  by both the environment and the genetic make up
  of the animal.

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Controlled Breeding Programs

• Outcrossing Breeding purebred animals with
  unrelated purebred animals.
• Cross Breeding Breeding animals of the same
  species but of a different breed.
• Hybrid Vigor or Heterosis
• A biological phenomenon which causes crossbreeds
  to out produce the average of their parents
• Will achieve 15 to 25 immediate increase in
  yield
• The more dissimilar the breeds, the greater the
  heterosis (British breed crossed with Zebu breed)

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Two-Breed Cross

• Purebred bulls X purebred cows of another breed
• 8-10 increase in weaning weight

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Two-Breed Backcross or Crisscross

• Breed A X Breed B Crossbred calves
• Crossbred X Breed A or B
• Charolais Bull X Hereford Cow Cross
• Cross X Charolais
• Yields 67 of maximum heterosis

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Three Breed Rotation Cross

• 3 Breeds (Angus, Simmental, Charolais)
• Crossbred females bred to purebred bull of breed
  A
• Resulting cross mated to purebred bull of breed B
• Resulting cross mated to purebred bull of breed C
• Repeat rotation
• 87 of maximum heterosis

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Gene Transfer

• All selection is based on the concept that
  desired characteristics are passed on from the
  parents to the offspring.
• Humans have 46 chromosomes. Each parent
  contributes 23.
• A chromosome is a long protein strand on
  molecules called DNA.
• DNA is made up of segments called genes.

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Gene Transfer

• Each gene is responsible for a particular trait.
• Genes form a code or a blueprint for how the
  animal is to be formed.
• One chromosome (strand of DNA) will attach to
  another forming a spiral shape called a double
  helix.

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Gene Transfer

• Each half is bound together by substances called
  nucleotides.
• There are four main nucleotides
• Adenine
• Thiamine
• Guanine
• Cytosine

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Gene Transfer

• Nucleotides are shaped so that each substance can
  pair with one particular nucleotide.
• Adenine can only pair with thiamine.
• Cytosine can only pair with guanine.
• When cells undergo mitosis and divide, each half
  replicates itself so two strands exactly alike
  are formed. (DNA replication).

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Gene Transfer

• The genetic sequence on the DNA is used as a
  pattern for how the animal is to be constructed.
  RNA (Ribonucleic acid) reads the pattern and
  transfers the information to the rest of the
  cell.

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Genetic Engineering

• Genetic engineering is a technology that allows
  specific genetic information or traits to be
  built into or engineered into the genes of a
  species.
• In genetic engineering, segments of DNA are cut
  and spliced into existing DNA, placing new
  genetic information into the existing DNA.

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Differentiation

• As the embryo begins to grow and develop, cells
  differentiate. Some cells develop into muscle and
  bone, some into skin and some into internal
  organs.
• The process of how cells differentiate is not
  fully understood.

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Differentiation

• Sex cells called gametes undergo meiosis and only
  carry one strand of DNA.
• At conception, chromosome halves from each parent
  combine to form a paired chromosome.
• There is almost an infinite number of ways that
  the genes can be arranged on a strand of DNA.
  This arrangement determines the make up of the
  new animal.

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Alleles

• Each male gene that controls a specific trait
  combines with the female gene for the same trait.
  
• A pair of genes that control a specific trait are
  called alleles.
• If both genes that control a specific trait are
  alike, they are said to be homozygous.
• For example, if the male gene for hair color is
  black and the female gene that controls hair
  color is also black.

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Gene Dominance

• If they are different (black red), they are
  said to be heterozygous.
• In this case one gene will be dominate and
  determine coat color.
• Dominant gene trait overpowers others
• Recessive gene must be accompanied with another
  recessive gene to express trait

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Gene Dominance

• P polled
• p horned
• Genotype is the genetic make up of the animal.
• Phenotype is the physical appearance of the
  animal.
• If a homozygous horned cow (pp) is mated to a
  homozygous polled bull (PP), what will the
  genotypic and phenotypic ratio of the calves be?

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Punnett Square
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Monohybrid Cross

• A monohybrid cross is an estimation of a
  predicted outcome for a single trait.
• If a homozygous horned cow (pp) is bred with a
  heterozygous polled bull (Pp), what percent of
  the calves will be polled?

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Monohybrid Cross
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Monohybrid Cross

• What results if two heterozygous animals are
  mated.

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Dihybrid Cross

• A dihybrid cross is a estimation of a predicted
  outcome for two traits.
• What results if an Angus bull that is homozygous
  black and polled (BBPP) is bred with a red
  shorthorn cow which is homozygous red and horned
  (bbpp).
• The bull BBPP can be simplified to BP (black
  polled is the only possible contribution for the
  bull).
• The cow bbpp can be simplified to bp (red
  horned is the only possible contribution for the
  cow).

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Dihybrid Cross
Black 100 Polled 100 Horned 0
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Dihybrid Cross

• Now if two of the offspring which are
  heterozygous for black/red and polled/horned
  (BbPp) are mated.
• How do you do a Punnett square for two
  heterozyous animals?
• Use all possible gene combinations.
• Both the bull and cow are BbPp.
• What are the possible contributions?
• BP, Bp, bP, bp for both animals. (4 x 4 grid)

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Dihybrid Cross
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Dihybrid Cross

• Black Polled 9 out of 16 or 56.25
• Black Horned 3 out of 16 or 18.75
• Red Polled 3 out of 16 or 18.75
• Red Horned 1 out of 16 or 6.25

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Dihybrid Cross

• If a heterozygous bull (BbPp) is mated to a
  homozygous cow (BBPP).
• What are the outcomes?

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Dihybrid Cross
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Dihybrid Cross

• If a (BbPp) bull is mated to a (BBPp) cow.
• what are the outcomes?

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Dihybrid Cross
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Mendilin Genetics

• Paint color is a desirable characteristic of
  paint horses and is dominate to solid color.
• If a homozygous dominate stallion is bred with a
  solid colored mare, how likely is it that a paint
  foal will result?
• What if the stallion is heterozygous for paint
  color?

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Codominate Genes

• Some alleles may have two dominate genes.
• Shorthorn cattle are red, white or roan.
• Red shorthorns carry the gene for red coat color
  RR.
• White shorthorns carry the gene for white coat
  color WW.
• Cattle that are roan or spotted carry a gene for
  red and a gene for white RW.
• Both are dominant, creating a spotted or roan
  colored animal.

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Shorthorn Red X White
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The Additive Expression of Genes

• Instead of a single pair, a number of genes may
  be added together to produce a single trait.
• Examples
• Milk production is controlled by several genes.
• Size and body capacity of the female
• Hormone production
• Mammary size and function
• Rate of gain
• Reproduction

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Genetic Mutations

• Occasionally a defect will happen and genetic
  traits are not passed on as intended.
• Example two headed calves
• An abnormality is similar to a mutation, only it
  is caused by something in the environment

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Genetic Mutations
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Genetic Mutations

• Sometimes genetic mutations can be used to
  introduce new kinds of species.
• Polled Hereford Cattle

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Determining an Animals Sex

• Whether a mammal is a male or a female is
  determined upon conception.
• Gamete (sex cell) contains one half of the sex
  chromosome from the parent.
• The female chromosome is referred to as XX.
• When the chromosome divides and half goes to the
  offspring each half is the same.

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Determining an Animals Sex

• The male chromosome is referred to as XY. And
  when divided, a gamete will be either X or Y.
• When the male and female gamete combine they will
  either be XX female or XY male.
• What is the probability of a male being conceived
  over a female child?

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What Sex Will the Offspring Be?
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Sex Determination