Genetics in Agricultural Breeding Programs

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Genetics in Agricultural Breeding Programs
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Natural Selection

• Mechanism for evolution in natural populations
• Organisms with best traits suited to the
  environmental factors affecting a population are
  most likely to survive and reproduce.
• Results in the inheritance of the same
  well-suited traits
• Important traits in natural selection-disease
  resistance, size, color pattern/camouflage, etc.

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Natural Selection

• Types of Natural Selection
• Stabilizing selection
• Directional selection
• Disruptive selection

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Stabilizing Selection

• Individuals with the average or norm for a trait
  have an advantage over other forms of the trait
• Example gray moths (norm) are favored over
  black and white moths

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Directional Selection

• Individuals with one extreme or less common
  version of a trait are favored over other forms
  of the trait.
• Example Black moths are favored over gray or
  white moths

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Disruptive Selection

• Multiple extremes or alternative forms of a trait
  are favored over the norm
• Example Black moths and white moths are favored
  over gray moths

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Selective Breeding

• Method of breeding plants and animals utilized in
  agriscience to produce offspring that possess
  certain characteristics desirable to
  agriculturists
• Utilized for generations-produced the first
  domestic animals in early civilizations

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Selective Breeding

• Used to select for a variety of traits including
• Muscling/Size
• Fat content
• Breeding Capability
• Color
• Speed/Agility
• Temperament
• Milk Production

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Selective Breeding

• Methods for selective breeding
• Artificial insemination
• Pen/field breeding
• Isolation Breeding-inbreeding
• Mechanical pollination of plants
• Hybridization of plants and animals

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Selective Breeding

• Selective breeding is accomplished much quicker
  in plants than animals due to growth rates and
  ease of propagation/production

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Selective Breeding Techniques

• Objective Summarize the process and purpose of
  selective breeding techniques

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Techniques in Animals

• Progeny testing is used to determine the value of
  male livestock by analyzing the transmission of
  traits to offspring and its breeding potential
• Artificial insemination has proven to have the
  greatest impact on animal breeding since the
  first domestication of livestock.

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Artificial Insemination

• Semen is collected from male individuals
  methods vary widely by the type of animal
• Artificial vaginas are used for larger mammals.
• Semen is checked for viability and flash frozen
  in specialized straws.
• Straws should be placed in storage tanks filled
  with liquid nitrogen, till use.
• Semen stored under proper conditions has proven
  viable decades later (-320ºF)
• Female is treated with prostaglandin (hormone) to
  induce estrus or heat
• Semen straws are immediately thawed in water
  (99ºF) and soon after inserted into the mother
  using a specialized release gun.

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Sperm Sexing

• Utilizes a cytometer cell sorter to separate male
  sperm from female sperm
• Sperm with X chromosomes (female sperm) weigh
  more (contain more DNA) than those with a Y and
  can thus be dyed and separated because they
  absorb more dye

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Invitro-Fertilization

• Method of removing eggs from a mother for
  fertilization under laboratory conditions.
• A large number of eggs are collected from the
  ovaries of an outstanding female and fertilized
  in Petri dishes under laboratory conditions
• Embryos can be inserted into surrogate mothers or
  frozen for later use
• Offers the most control and requires the least
  amount of semen.

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Birth Through Surrogate Mothers

• Hormones are used to cause the female to
  superovulate (produce a large number of eggs).
• Original mother undergoes artificial insemination
• Fertilized eggs are removed by a process called
  FLUSHING to be placed in other female animals for
  development.

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Cross-Pollination in Plants

• Method used to select particular parents for the
  production of seed in plants.
• Process
• Plants possessing desirable characteristics are
  selected and carefully monitored
• Pollen can be gathered from male plants (or
  flowers) months or in some cases, years in
  advance and refrigerated for storage
• Flowers on the female part must be covered prior
  to opening, and if capable of self-pollination,
  must have the stamens removed.
• Once the female flowers open, pollen from the
  male should be placed on the stigma, and the
  flower covered again.
• Record keeping is critical in crossing plants.

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Selecting Plants and Animals for Breeding
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Observe Patterns of Heredity

• The occurrence of genetic disorders in offspring
  or parents is an indicator that the parent may
  have a recessive gene for the disorder
• Though genetic recombination is random, some
  animals are more likely to transmit genes than
  others
• Keeping careful breeding records improves
  effectiveness

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Select Animals Carefully

• Along with a good genetic background, animals
  used in selective breeding should be
• Healthy-old injuries or illnesses are not a
  factor unless they are a result of genetic
  propensities or impair breeding capabilities
• Carefully monitored-nutrition levels, pests and
  stress can all reduce breeding viability. Some
  very good specimens are completely isolated.

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Select Animals Carefully

• Hybrids should be avoided, since traits expressed
  in the organism are rarely transmitted to
  offspring
• The process of inbreeding isolates genes for only
  a single generation, as many are recessive.

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Carefully Plan Breeding Crosses

• Plants can be crossed not only within species
  (interspecific), but also within genus
  (intergeneric), and even, in rate cases family
  (interfamilial)
• Animals are usually limited to crosses within the
  same species

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Methods for Producing Selective Breeding Programs
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Inbreeding

• Crossing organisms that are genetically related
• Crossing two plants to produce an f1 generation,
  then crossing two of the f1 offspring to create
  an f2 generation

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Backcrossing

• Crossing offspring from a cross with one of the
  previous parents, or a similar organism, to
  maximize the expression of certain traits.
• Often used after intergeneric crosses to produce
  offspring that possess more characteristics from
  one genus.