Punnett Squares (PowerPoint download) by yurtgc548

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									Mendelian
Genetics
            1
Gregor Mendel
  The Father of Genetics




                           2
             Gene
• A discrete unit of hereditary
  information consisting of a
  specific nucleotide sequence in
  DNA (or RNA in some viruses)


                                    3
                   Alleles
• •Alleles are alternate forms of a gene.
• •Examples: tall and short for plant height or purple
  or white for flower color.
• •Every trait has at least two alleles- one from each
  parent.
• •The location of an allele on a chromosome is
  known as its locus (loci = plural form).


                                                     4
          Genotype
• •The letters that represent
  (symbolize) the trait being
  investigated. The genetic make-
  up of an organism.
• •Examples: Bb, BB, bb

                                    5
           Phenotype
• The actual representation of the genes.
  The Physical appearance or traits in an
  organism resulting from its genetic
  makeup (what you see).
• Examples: tall, purple flower or white
  flower, blond hair, freckles, etc.

                                            6
          Dominant
• The allele that is fully expressed
  in an organism (observed).
• •Represented by capital letters.
• •Tall = T


                                   7
          Recessive
• •The allele that is masked by
  the dominant allele.
• •Represented by lower case
  letters.
• •Short = t
                                  8
        Homozygous
• When both alleles (letters) are
  the same.
• BB = Homozygous Dominant
• bb = Homozygous recessive


                                    9
       Heterozygous
• When the alleles (letters) are
  different.
• One upper case letter and one
  that is lower case.
• Bb = Heterozygous
                                   10
      Example Problem
• Round = R
• wrinkled = r
• If a plant has round seeds, do we
  know what its genotype is?
• It could be RR or Rr
• If a plant has wrinkled seeds, do
  we know what its genotype is?
• Yes, it is rr.                      11
       Punnett Square
• A method for finding predicted
  outcomes and probabilities for
  offspring from any cross.
• A chart for predicting the traits
  of offspring.

                                      12
     Some more terms:
• P-generation is the parental generation.
• The p-generation produce the F1
  generation.
• The F1 generation crossed with itself
  produces the F2 generation.


                                         13
Example Problem




                  14
• In foxes, red coat color is determined by
  the dominant gene R; silver-black coat is
  determined by the recessive gene r. A
  homozygous (pure) red male is crossed
  with a silver-black female. (The P
  generation).
 1.What is the genotype of the
 female?
                                              15
    What are the genotype
percentages of their offspring?
•First…make a Punnett square
for showing your work




                               16
Example Problem
       R          R

  r   Rr      Rr

  r   Rr      Rr
                      17
        Assignment
• Section 32-3




                     18
Assignment
 33-4 & 33-5


               19
              B = Brown   1 point
#1            b = blue

         B          b

     b   Bb         bb

     b   Bb         bb
                              20
                              1 point
 #1
• 1/2 or 50% chance of blue-eyed.

• 1/2 or 50% chance of Brown-eyed.



                                    21
         T = Tall     1 point
#2       t = short
          T          t

     t   Tt          tt

     t   Tt          tt
                          22
#2 What fraction of           1 point

offspring would be tall?

• 1/2 or 50% would be Tall.




                                  23
         W = White   1 point
#3       w = black
          W          w

     W   WW          Ww

     w   Ww          ww
                          24
                              1 point
#3a What fraction of the
offspring will be white?

• 3/4 or 75% will be white.



                                  25
                              1 point
#3b What fraction of the
 offspring will be black?
• 1/4 or 25% will be black.



                                  26
                            1 point
#3c What fraction of each
 genotype will you get?
 • 1/4 or 25% will be WW
 • 1/2 or 50% will be Ww
 • 1/4 or 25% will be ww.

                                27
                              1 point

#3d What fraction of each
 phenotype will you get?
• 3/4 or 75% will be White.
• 1/4 or 25% will be black.

                                  28
     RR = Red         1 point
     WW = White
#4   RW = Roan
                  R   R

       W     RW       RW

       W     RW       RW
                           29
                             1 point

 #4 Give the fraction of
 each color of offspring?
• 1/1 or 100% will be Roan - RW.


                                   30
     RR = Red         1 point
#5   WW = White
     RW = Roan
                  R   W

        W     RW      WW

        W     RW      WW
                          31
                             1 point

 #5 Give the fraction of
 each color of offspring?
• 1/2 or 50% will be Roan - RW.
• 1/2 or 50% will be White - WW.


                                   32
      G = Green       1 point
#1a   g = red
                  G   g

        G       GG    Gg

       g        Gg    gg
                           33
                           1 point

#1a Give the fraction of
   each genotype of
      offspring?
• 1/4 or 25% will be GG.
• 1/2 or 50% will be Gg.
• 1/4 or 25% will be gg.
                               34
      G = Green       1 point
#1b   g = red
                  G   g

        g       Gg    gg

       g        Gg    gg
                           35
                           1 point
#1b Give the fraction of
   each genotype of
      offspring?
• 1/2 or 50% will be Gg.
• 1/2 or 50% will be gg.

                               36
                              1 point
#2a What is the fraction
  of each phenotype?
• 3/4 or 75% will be Green.
• 1/4 or 25% will be red.


                                  37
                             1 point
#2b What is the fraction
  of each phenotype.
• 1/2 or 50% will be Green
• 1/2 or 50% will be red.


                                 38
                       b          b
   #3
               B     Bb          Bb
     1 point


               b     bb           bb

•The mother had to be heterozygous or Bb
since the couple had a blue eyed child.
                                       39
                                1 point
 #4
•There would be a 50% chance that the
2nd child from the couple would have a
brown eyes.




                                    40
                               2 points
 #5             The couple had two
                spotted and two
• Spotted = S
                white kittens.
• white = s
• Mother = ss since she is white.
• Father’s Genotype would be Ss.
• Father’s Phenotype would be
  Spotted
                                    41
                                5 points
 #6
• Man has blue eyes - bb.
• G-Ma has blue eyes - bb.
• Woman has brown eyes - Bb.
• 50% of children would be Bb. (Brown)
• 50% of children would be bb. (Blue)

                                     42
Please put a score on top
     of their paper.
 • Put the number correct out of
               28



                                   43
         Punnett Squares
• Why are punnett squares useful?
• We can use a punnett square to predict the
  probable genotypes and phenotypes for
  offspring from a genetic cross.
• Genotype = What is inside the genes, the
  make-up.
• Phenotype = The outward expression of
  the genes.                           44

								
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