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Genetics

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					Genetics
         Genetics
• the study of heredity
• the way in which traits of
  parents are passed on to
  offspring
  Father of Genetics
• Gregor Mendel
• Austrian monk
• did experiments with peas
  and proved that certain
  characteristics……..
          ……….
• Such as color and height, are
  passed from parent to
  offspring
       Differences
• all differences in organisms
  are not caused by genetics
• some are caused by the
  environment
• the conditions under which
  the animals are raised
    Parts of the cell
• cell membrane - contains the
  cytoplasm and the nucleus
        Cytoplasm
• protects and cushions the
  nucleus
          Nucleus
• contains the genetic material
     Chromosomes
• carry the genes
• exist in pairs in all cells
  except sperm and egg cells
           Genes
• single determiner of a
  hereditary trait
      Cell Division
• two types
• Mitosis
• Meiosis
          Mitosis
• cell division for growth
• this division never ends
• chromosome pairs are
  duplicated exactly alike
          Mitosis
• each new cell is exactly like
  the old ones
• asexual division
• chromosomes are in pairs
          Mitosis
• steps of mitosis
• Prophase (Interphase)
• Metaphase
• Anaphase
           Steps
• Telophase
• Cytokinesis
• ** PMATC
          Meiosis
• cell division of reproductive
  cells (sperm and egg)
• each new cell is not exactly
  like the old one
         Meiosis
• in each new cell
  chromosomes are not in pairs
• each new cell contains half
  of the original number of
  chromosomes
          Meiosis
• allows for random
  assortment of parental genes
          Gamete
• mature egg or sperm cell
• each gamete has half the
  original number of
  chromosomes
     Dominant gene
• in a pair, hides the effect of
  another gene
     Recessive gene
• the gene which is hidden by a
  dominant gene
        Examples
• of dominant genes
• tongue rolling
• free ear lobes
• polled cattle
         Examples
• of recessive genes
• color red in Holsteins
• dwarfism
         Symbols
• dominant genes
• capital letters
          Symbols
• recessive genes
• lower case letters
      Homozygous
• gene pairs
• one which carries two genes
  for a trait
• both represented by capital or
  lower case letters
      Homozygous
• polled - PP
• horned - pp
     Heterozygous
• gene pairs
• one which carries one
  dominant and one recessive
  gene
       Heterozygous
• Pp
         Genotype
• genetic makeup of an animal
  or a given trait expressed by
  symbols
• Ex: PP, AA, Pp, Aa, aa
        Phenotype
• physical appearance
  expressed in words
• Ex: polled, horned
    T t
          Mitosis

T         t
                  Meiosis

                  Mitosis
    t         t
    Steps of Meiosis
• Prophase I ( Interphase)
• Metaphase I
• Anaphase I
• Telophase I
    Steps of Meiosis
• Prophase II (Interphase)
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis
              If
• two heterozygous animals
  are mated
• the number of traits being
  selected is six
• the total number of offspring
  is over 16,000,000
        Incomplete
        Dominance
• when one gene does not hide
  the effect of the other in a
  gene pair
• result is a mixture of the two
  traits
       Incomplete
       Dominance
• Roan coloring in cattle
• RR X WW = RW
• Red X White = Roan
• Roan - mixture of red and
  white hairs
  Sex determination
• male sex chromosomes
• male mammals have two
  different sex chromosomes
• XY
• females are XX
  Sex determination
• poultry
• the female determines the sex
  of the offspring
• female is ZW
• male is ZZ
   Sex Linked Traits
• genes which are carried only
  on the sex chromosomes
• ex: red green color blindness
• 2:25 males
• 1:150 females
  Sex Linked Traits
• hemophilia
• bleeders’ disease
• more common in males than
  in females
   Sex Linked Traits
• barred feather pattern vs
  black in chickens
          Mutation
• when a new trait is shown
  that did not exist in either
  parent
         Mutation
• the new breed of polled
  Herefords
• which resulted from the
  crossing of two horned
  animals
 Causes of Mutations
• radiation (nuclear accident or
  x-ray)
• chemicals
 Systems of breeding
• purebreeding
• inbreeding
• outcrossing
• grading up
• crossbreeding
      Purebreeding
• purebred is defined as a
  member of a breed
• the animals of which possess
  a common ancestry
• distinctive characteristics
       Purebreeding
• is registered or eligible for
  registry
       Outcrossing
• mating of animals of
  different families within the
  same breed
• relatively safe system of
  breeding
       Outcrossing
• unlikely that two unrelated
  animals would carry the
  same undesirable genes and
  pass them on
        Grading up
• mating of purebred sires to
  grade females
• relatively inexpensive and is
  dependent upon the quality
  of the sire
        Inbreeding
• mating of related animals
• closebreeding - a form of
  inbreeding
• most intensive form
• animals are very closely
  related
      Closebreeding
• sire to daughter
• son to dam
• brother to sister
     Closebreeding
• was used on foundations but
  is not used much today
• used in the development of
  the Quarter Horse breed
     Closebreeding
• animals are more uniform
• more chance for undesirable
  recessive gene expression
      Linebreeding
• refers to the mating of
  animals which are more
  distantly related
• cousins, grandparents, half
  sibling
      Linebreeding
• used favorably today because
  there is less chance of
  expression on undesirable
  recessive traits
      Linebreeding
• less chance of genetically
  superior stock
• considered middle of the
  road
     Crossbreeding
• mating of animals from
  different breeds
• often causes hybrid vigor
      Hybrid Vigor
• causes crossbreds to
  outproduce the average of
  their parents
• some breeds cause hybrid
  vigor better than others
      Hybrid Vigor
• breeding a British breed,
  Angus, to an Indian Breed<
  Brahman
• compared to an Angus X
  Shorthorn cross
     Hybrid Vigor
• Angus X Brahman would
  have more hybrid vigor
        Selection
• based upon
• type
• pedigree
• showring winnings
• production records

				
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