Genetics

							Genetics

 Chapter 4
              Genetics
• Is the science of heredity.
• Heredity is the transmission of genetic
  or physical traits from parent to
  offspring.
          Gregor Mendel
• Austrian Monk
• Considered the “Father of Heredity”
• He conducted plant breeding
  experiments in their monastery
  garden.
• In 1865 he made his work public, units
  of inheritance.
    What makes us unique?
• Each of the 100 Trillion cells in our
  body except the red blood cells
  contains the entire human genome, in
  the nucleus of every cell is the genetic
  information “blueprint” to construct
  the individual.
• It is the Deoxyribonucleic acid (DNA)
• Function of DNA
  – Genetic code for almost every organism.
  – Provide template for protein synthesis.
       Composition of DNA
• The structure of DNA was discovered by
  Watson and Crick in 1953.
• It is a twisted double helix molecule,
  containing sugar, phosphates, and
  nitrogenous bases.
• The sugar is deoxyribose and the
  phosphoric acid molecules are always the
  same and provides for the structure (side of
  the ladder).
• The only difference between us is the order
  and arrangement of the four bases (rungs of
  the ladder).
          Bases of DNA
• Adenine= A
• Thymine= T
• Guanine= G
• Cytosine= C
• A always pairs with T
• C always pairs with G
          Bases of RNA
• Adenine= A
• Uracil= U
• Guanine= G
• Cytosine= C
• G always pairs with C
• T from the DNA = A in the RNA
• A from the DNA = U in the RNA
DNA Model
          Chromosomes
• The DNA in every cell is located in
  rod like segments called chromosomes
• Chromosomes occurs in pairs in every
  cell of our body except in the sperm
  and ovum.
• Chromosomes numbers are the same
  for each specie.
    Chromosome Numbers
Specie    Diploid #   Haploid #
Cattle    60          30
Swine     38          19
Sheep     54          27
Horse     64          32
Human     46          23
Chicken   78          39
Goat      60          30
Donkey    62          31
          Chromosomes
• There are 2 sex chromosomes included
  in the diploid number of the
  chromosomes.
• All of the other chromosomes are
  referred to as autosomes.
• In mammals if the sex chromosomes
  are alike, XX it results in a female.
• If the sex chromosomes are different,
  XY it results in a male.
        Sex Determination
• Female can contribute only a X chromosome
  towards the sex of their offspring.
• Male can contribute an X or a Y
  chromosome toward the sex of their
  offspring.
• Absence of an Y chromosome results in a
  the embryo developing into a female.
• Presence of an Y chromosome results in the
  embryo developing into a male.
Sex Determination
         • Gametogenesis =
           Formation of
           gametes through
           meiosis.
         • Male = 4 viable
           spermatids
         • Female = 1 viable
           ovum, 3 polar
           bodies.
Tell me what I am ?????
Tell me what I am ?????
              Cell Division
• Meiosis
  – Is the form of cell division which results
    reducing the chromosome number from the
    diploid # to the haploid #.
  – Occurs only in the sex cells, sperm and ovum.
• Mitosis
  – Is the form of cell division which results in the
    formation of identical daughter cells, keeps the
    chromosome number constant.
  – Tissue growth and repair.
  – Occurs throughout the body except in the sex
    cells.
      Genotype or Gamete
• Genotype contains two copies of the
  gene.
  – AaBB
• Gamete (sex cells) contains only one
  copy of the gene.
  – AB
• Determine the possible gametes of
  AaBB
  – AB        aB
      Gamete or Genotype
• State if its a gamete or genotype.
• Aa
•D
• DdEeFFgg
• sRtxyq
• AaBBeeFF
• adgEFT
 List all the possible gametes.
• From the genotype AaBb
• AB
• Ab
• aB
• ab
                Genes
• Chromosomes contains several units
  of inheritance “genes”.
• Genes usually occurs in pairs, one
  from each parent.
• Some traits are inherited directly from
  one set of genes.
• Some traits are inherited through
  several sets of genes.
                 Genes
• It was presumed that we were
  composed of about 100,000 genes to
  construct us.
• Today, research has proven that
  number is a lot less than 100,000.
• Extra credit for the student that can
  find an article about the current
  number of genes.
           Terms to know
• Homozygous- contains 2 identical genes for
  the same trait, AA, BB, cc
• Heterozygous- contains 2 different genes
  for the same trait, Aa, bB, Cc
• Phenotype- Outward appearance of a trait,
  coat color, polled, horned.
• Genotype- Genetic classification of a gene,
  AA, Aa, aa.
• Allele- Location of a gene on the
  chromosome.
• F-one = First cross mating.
• F-two = Second cross mating.
  What are dominant genes?
• The gene that express itself, the powerful
  and dominant gene.
• It has the power to overshadow the
  recessive gene when there is complete
  dominance.
• Some examples are:
  –   White faced in cattle
  –   Droopy ears in swine
  –   Polled in cattle
  –   Black coat color in Angus cattle
 What are Recessive Genes?
• The gene that is overshadowed by a
  dominant gene
• Recessive genes can only express
  themselves in the absence of the
  dominant gene
• Polled vs Horned (Pp) (pp)
• Black wool vs white (Ww) (ww)
• Dwarfism vs normal size (dd)
• Albino
           Punnet Square
• Angus- Black coat color is dominant.
• BB = Homozygous Dominant and Black
• Bb = Heterozygous and is black
• bb = Homozygous recessive and red
• A heterozygous bull is mated to 50
  homozygous recessive cows.
• How many calves are black?
• How many calves are red?
• What is the genotypic and phenotypic
  ratios?
    Punnet Square

     B       b
b    Bb      bb
b    Bb      bb
                 Results
• 2 heterozygous =
  Bb
• 2 Homozygous
  Recessive bb
• 25 Black, 25 Red
• Genotypic ratio =
  0:2:2
• Phenotypic ratio =
2 Black: 2 Red
What are Sex Linked Genes?
• Some recessive genes are attached to
  the X and Y chromosomes
• Humans: Colorblindness and
  Baldness are on the X chromosomes
• In Men, traits expressed anytime
  present
• In Women, must have two recessives
  to show trait
• Children get baldness from mothers
    If Dad is bald, will you be
               bald?
           X B        Y




X         X X B        X    Y




X         X X B       X Y
    Baldness is carried by the
            mother
          X          Y




X B       X X B       XBY




X        X X         X Y
      What if Mom is bald?
        X          Y




X B     X X B       XBY




X B     X X B      XBY
        What is Incomplete
          Dominance?

• If both genes express themselves
• Shorthorn Cattle: Red male mated to a
  White female = Roan calf
• RR crossed rr = Rr
           Punnet Square
• Shorthorn Cattle
• RR = Red
• rr = white
• Rr = roan
• If a red bull (RR) is mated to a white
  cow (rr), what color will the calves be?
Shorthorn: Red X White
    R        R

r Rr          Rr
r Rr          Rr
           Punnet Square
• If a red bull (RR) is mated to a roan
  (Rr) cow, what color will the calves
  be?
Shorthorn: Red X Roan
     R       R
R    RR      RR
r     Rr      Rr
What if Both Parents are
         Roan?
       R         r
R     RR         Rr
r       Rr        rr
      What is a Mutation?
• Dramatically different from what is
  expected genetically
• Horned calf from polled parents
• Loss of some or extra body parts
• Lethal Mutation: causes death at birth
• Sublethal Mutation: limits animals
  ability to grow to maturity
• Beneficial Mutation: loss of tail in
  lambs
      What is Heritability?
• Chance that traits will be inherited
• Low: multiple births, fat covering
• Medium: birth wt, wean wt, milk,
  wool grade, carcass wt, rate of gain
• High: Loin eye area, fleece length &
  quality
          Mating Systems
• Upgrading: mating purebreds with grade
  animals
• Inbreeding: mating closely related animals
• Linebreeding: mating distantly related
  animals
• Outcrossing: mating unrelated animals in
  the same breed.
• Crossbreeding: mating animals of same
  species but different breeds.
      What is Hybrid Vigor?
            Heterosis
• Offspring will outperform either of the
  parents
• Corn Breed A yields 100 bu/acre
• Corn Breed B yields 100 bu/acre
• Crossbreed A & B yields corn that
  yields 200 bu/acre
• Vigor only expressed in crossbreeding
              The End
• You can use your notes to do the next
  two worksheets.