Mendelian Genetics - PowerPoint by gjjur4356

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									                 Mendelian Genetics
Augustinian                                   While assigned to
Monk at Brno                                  teach, he was also
Monastery in                                  assigned to tend
Austria (now                                  the gardens and
Czech Republic)                               grow vegetables
                                              for the monks to
Not a great teacher                           eat.
but well trained in
math, statistics,                             Mountains with
probability,                                  short, cool growing
physics, and                                  season meant pea
interested in plants                          (Pisum sativum)
and heredity.            Gregor Mendel        was an ideal crop
                       “Father of Genetics”   plant.
Contributions in 1860s (US Civil War Era)
  • Discovered Genes as Particles of Inheritance
  • Discovered Patterns of Inheritance
  • Discovered Genes Come from Both Parents
                              http://forensicservices.utah.gov/biology/pictures/sperm.jpg
    Egg + Sperm = Zygote
                                             QuickTime™ and a
                                   TIFF (Un compresse d) decompressor
    Nature vs Nurture               are needed to se e this picture.

    Sperm means Seed (Homunculus)




                                                                                            http://academic.evergreen.edu/v/vivianoc/homunculus.gif
  • Discovered One Form of Gene (Allele) Dominant
    to Another
  • Discovered Recessive Allele Expressed in
    Absence of Dominant Allele
Mendel worked with peas (Pisum sativum)
    • Good choice for environment of monastery
    • Network provided unusual varieties for testing
    • Obligate self-pollination reproductive system
        Permits side-by-side genetic barriers
        Cross-pollinations require intentional process

    • Crosses meticulously documented
    • Crosses numerically/statistically analyzed
    • Scientists of 1860s could not understand math
    • Work lost in journals for 50 years!
    • Rediscovered in 1900s independently by 3 scientists
    • Recognized as landmark work!
One Example of Mendel’s Work
          Tall                x            Dwarf              Phenotype
P
          DD                                dd                Genotype
      Homozygous                          Homozygous
       Dominant                            Recessive
                          All Tall           Clearly Tall is Inherited…
F1                                           What happened to Dwarf?
                            Dd
                        Heterozygous         1.       Tall is dominant to Dwarf
                                             2.       Use D/d rather than T/t for
                                                      symbolic logic
                       F1 x F1 = F2
                       possible gametes
     Punnett Square:    D            d
                                             3/  Tall
F2                 D
                       Tall        Tall           4
                                             1/ Dwarf
        possible       DD          Dd          4
        gametes        Tall       Dwarf      Dwarf is not missing…just masked
                   d                         as “recessive” in a diploid state…
                       Dd          dd
                                             there IS a female contribution.
Mendel as a Scientist                          F2                F1 x F1 = F2
                                                                 possible gametes
                                           Punnett Square:
Test Cross:                                                       D           d
   Unknown Tall     x   Dwarf                               D
                                                                 Tall        Tall
                         dd                   possible           DD          Dd
                                              gametes            Tall      Dwarf
                        possible gametes                     d
If Unknown is DD:                                                Dd         dd
                          d          d
                         Tall      Tall
                    D
         possible        Dd        Dd
         gametes                               Test Progeny All Tall
                         Tall      Tall
                    D
                         Dd        Dd
                                                1/       of F2 Tall are DD
                                                     3
                        possible gametes
If Unknown is Dd:                               2/
                          d          d               3   of F2 Tall are Dd
                         Tall      Tall
                    D
         possible        Dd        Dd
         gametes                               Test Progeny Half Tall
                        Dwarf     Dwarf
                    d                                    Half Dwarf
                         dd        dd
Another Example of Mendel’s Work
         Green                  x             Yellow             Phenotype
P
          gg                                   GG                Genotype
      Homozygous                             Homozygous
       Recessive                              Dominant
                        All Yellow             Clearly Yellow is Inherited…
F1                                             What happened to Green?
                            Gg
                        Heterozygous            1.       Yellow is dominant to Green
                                                2.       Use G/g rather than Y/y for
                                                         symbolic logic
                       F1 x F1 = F2
                        possible gametes                 NEVER use G/Y or g/y
     Punnett Square:     G            g
                                                3/  Yellow
F2                 G
                       Yellow       Yellow           4
                                                1/ Green
        possible        GG           Gg           4
        gametes        Yellow       Green       Green is not missing…just masked
                   g                            as “recessive” in diploid state
                        Gg           gg
Mendel as a Scientist                           F2              F1 x F1 = F2
                                                                 possible gametes
                                            Punnett Square:
Test Cross:                                                       G           g
   Unknown Yellow x        Green                            G
                                                                Yellow    Yellow
                            gg                 possible          GG        Gg
                                               gametes          Yellow     Green
                         possible gametes                   g
If Unknown is GG:                                                Gg         gg
                          g           g
                        Yellow     Yellow
                    G
         possible        Gg         Gg
         gametes                               Test Progeny All Yellow
                        Yellow     Yellow
                    G
                         Gg         Gg
                                               1/       of F2 Yellow are GG
                                                    3
                         possible gametes
If Unknown is Gg:                              2/       of F2 Yellow are Gg
                          g           g             3

                        Yellow     Yellow
                    G
         possible        Gg         Gg
         gametes                                Test Progeny Half Yellow
                        Green      Green
                    g                                         Half Green
                         gg         gg
Mendel as a Scientist
                                             Actual Results             Decision
Test Cross:
                                            3 Yellow 2 Green                Gg
   Unknown Yellow x        Green
                            gg              2 Yellow 3 Green                Gg
                         possible gametes   1 Yellow 4 Green                Gg
If Unknown is GG:
                          g           g      Small families do not follow
                        Yellow     Yellow    expected ratios perfectly!
                    G
         possible        Gg         Gg      0 Yellow 5 Green                Gg
         gametes        Yellow     Yellow    Rare, but it can happen!
                    G
                         Gg         Gg      4 Yellow 1 Green                Gg
                                             It only takes 1 green to be sure
                         possible gametes    the unknown is Gg!
If Unknown is Gg:
                          g           g     5 Yellow 0 Green                GG
                        Yellow     Yellow          <5% chance unknown is Gg
                    G
         possible        Gg         Gg       1/     • 1/2 • 1/2 • 1/2 • 1/2 = 1/32
                                                  2
         gametes        Green      Green
                    g                             You could be wrong (rarely)!
                         gg         gg
                                             After 1900 several scientists tried to
Genetics After Mendel                        replicate Mendel’s crosses using other
                                             species including snapdragon.
      Red                Yellow
P                  x
      PRPR                PYPY

                                 When these alleles go walking, they both do
                                 some talking (codominance)!
          All Orange
F1                               OK, so we cannot use R/r nor Y/y so we pick
             PRPY                a third letter…P for the petal color gene.
                                 Notice: we do NOT mix R/Y or r/y!
        F1 x F1 = F2
                         possible gametes
     Punnett Square:     PR           PY
F2                 PR
                        Red        Orange        This F2 will NOT have a 3:1 ratio
                                                 of phenotypes.
        possible        PRPR        PRPY
        gametes         Orange     Yellow        Instead it shows a 1:2:1 ratio!
                   PY
                         PRPY       P YP Y       The exception here proves the rule.
In addition to this, there are multiple alleles possible:
      PR = red PY = yellow p = no pigment

The combination of alleles in a diploid determine the flower color:
     PRPR = red                PRp = pink
     PRPY = orange             PYp = cream
     PYPY = yellow             pp = white

Human hair color follows a similar pattern:
      Alleles: HBn = brown HBd = blonde hR = red hbk = black
The combinations of these alleles determine the base hair color:
    HBnHBn = dark brown HBdHBd = blonde            hRhR = red
    HBnHBd = sandy brown HBdhR = strawberry hRhbk = red
    HBnhR = auburn                    blonde
    HBnhbk = dark brown HBdhbk = blonde            hbkhbk = black
                                                  Recessive can
      Dominant does NOT mean frequent!
                                                   be common!
 Another Example of Recessive Being Common: Pisum sativum
  Garden Peas: green seed, wrinkled seed, dwarf stature, white flower
                   gg           ww            dd              aa
                   In other words: a quadruple double-recessive
                     is the most common garden pea on Earth!
 Quantitative Inheritance: multiple genes control trait
              Highest Crop Yield: AABBCCDDEE
         Intermediate Crop Yield: AabbCCDdEe
               Lowest Crop Yield: aabbccddee

                 Darkest Skin Color: AABBCCDDEE
            Intermediate Skin Color: AaBbCcDdEe
                 Lightest Skin Color: aabbccddee
AaBbCcDdEe x AaBbCcDdEe can produce a huge range of colors!
    Yet TV talk show guests argue this point for Maury, etc.
Phenotype = Genotype + Environment
   Crop Yield = Genotype
                 + Minerals       Optimizing these
                    + Water       factors determines
                    + Light       agricultural
                     - Pests      productivity…last
                        etc.      part of our course!


   Human Skin Color = Genotype
                         + Sun (UV) Exposure
                               - Aging Factors
          The sun exposure effect is most obvious in
           people of intermediate skin base color
             but everyone can have “tan lines.”
Who Gets To Mate With Whom?                       …Two Extremes
  Inbreeding Depression: related parents give same recessives to children
     Hemophilia: Queen Victoria’s Mutation and Diseased Grandchildren
     Tay-Sachs: Jewish Populations             Incest Taboo…but
     Bipolar: Irish Populations
     Dog Diseases: German Shepherd hip dysplasia

  Hybrid Vigor: recessives of one family are “covered” by dominant of other family

    Wild Corn A x Wild Corn B
                                            “Half-breed” is better
       High Yield Hybrid Corn!

    Are Human Cultures of “Great Melting Pots” Superior?
                  “Mutt” is best dog!
Mechanisms Preventing Inbreeding in Plants
   Evolution of Unisexuality: Dioecious Holly and Kiwi
          Common Gardener Error at Nursery Pickup

    Timing Separation of Bisexuality
          • Protandry: Male First, Then Female (Alstromeria, Campanula)
          • Protogyny: Female First (Oenothera)
          • Sequence in Cucumis: Male, Bisexual, Female, Parthenocarpic

   Self-Incompatibility: Sweet Cherry, Almond, Filbert
          • pollen germination prevented
          • pollen tube growth halted
          • synergid action (sperm release) prevented
          • sperm deactivated
Going Outside the Box of a Species: Bread Wheat
 AA (diploid wheat)                     x         DD (diploid grass)
    Triticum urartu                                 Aegilops tauschii


      AD (sterile diploid)   colchicine   AADD
      similar to mule!     or spontaneous (fertile tetraploid)


  BB (diploid grass)
    Aegilops speltoides

                                                 BBAADD
                                colchicine
       BAD (sterile triploid)                 Fertile hexaploid
                              or spontaneous
                                               Bread Wheat
                                             Triticum aestivum
Bread Wheat Created 7500 BC with spontaneous doubling of DNA
         Levy A. A. and M. Feldman. 2002. The impact of polyploidy on grass genome evolution. Plant Physiol. 130: 1587-1593.
Yet Another Example of Mendel’s Work
         Wrinkled              x               Round               Phenotype
P
          ww                                    WW                 Genotype
      Homozygous                              Homozygous
       Recessive                               Dominant
                        All Round               1.        Round is dominant to Wrinkled
F1
                            Ww                  2.        Use W/w rather than R/r for
                        Heterozygous                      symbolic logic: in handwriting
                                                          make it legible!   Ww
      F1 x F1 = F2                                   NEVER use W/R or w/r
                       possible gametes
     Punnett Square:    W             w
F2                 W
                       Round        Round
                                                 3/
        possible        WW           Ww              Round
                                                      4
        gametes        Round       Wrinkled      1/ Wrinkled
                   w                               4
                        Ww           ww
Mendel as a Scientist                          F2            F1 x F1 = F2
                                                             possible gametes
                                           Punnett Square:
Test Cross:                                                   W          w
   Unknown Round x        Wrinkled                       W
                                                             Round     Round
                           ww                 possible        WW        Ww
                                              gametes        Round   Wrinkled
                        possible gametes                 w
If Unknown is WW:                                             Ww       ww
                         w          w
                        Round     Round
                    W
         possible        Ww        Ww
         gametes                               Test Progeny All Round
                        Round     Round
                    W
                         Ww        Ww

                        possible gametes
If Unknown is Ww:
                          w         w
                        Round     Round
                    W
         possible        Ww        Ww
         gametes                               Test Progeny Half Round
                      Wrinkled Wrinkled
                    w                                    Half Wrinkled
                        ww       ww
Mendel as a Scientist
                                              Actual Results             Decision
Test Cross:
                                             3 Round 2 Wrinkled Ww
   Unknown Round x          Wrinkled
                             ww              2 Round 3 Wrinkled Ww
                          possible gametes   1 Round 4 Wrinkled Ww
If Unknown is WW:
                           w          w       Small families do not follow
                         Round      Round     expected ratios perfectly!
                    W
         possible         Ww         Ww      0 Round 5 Wrinkled Ww
         gametes         Round      Round     Rare, but it can happen!
                    W
                          Ww         Ww      4 Round 1 Wrinkled Ww
                                              It only takes 1 wrinkled to be
                          possible gametes    sure the unknown is Ww!
If Unknown is Ww:
                           w          w      5 Round 0 Wrinkled WW
                         Round      Round           <5% chance unknown is Ww
                    W
         possible         Ww         Ww       1/     • 1/2 • 1/2 • 1/2 • 1/2 = 1/32
                                                   2
         gametes        Wrinkled Wrinkled
                    w                              You could be wrong (rarely)!
                          ww       ww

								
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