Probability Punnett Squares

							 PROBABILITY &
PUNNETT SQUARES




      Mrs. Sinkaus
    Academic Biology
        Fall 2008
             BELL RINGER




            What do these pictures show?
What is unusual about this hand and foot? Look closely!!
BELL RINGER CONT.

              •The hand and foot
              have six fingers and
              toes instead of five.

              •This is the result of
              a genetic disorder
              referred to as
              Polydactyly –
              having more than
              five digits.
          BELL RINGER CONT.


                              What religious group
                             do these people belong
                                       to?




 They are Amish - lead a
  simple life centered on
family and religion. Large
   population resides in
  Lancaster County, PA.
         BELL RINGER CONT.
The Amish live separately
 from the rest of society.
They typically marry only
   other Amish people.
    What if I told you
   Polydactyly is more
   common among the
    Amish than in the
general population. Why
do you think that is true?


             Why might it someday be important for you
             to know if you are a carrier for a genetic
             disease?
OBJECTIVES
As a result of this lesson you (my students)
will be able to:

•Explain how geneticists use the principles of
probability
•Describe how geneticists use Punnet Squares
•Distinguish between the concepts heterozygous and
homozygous
•Solve genetic problems using a Punnet Square
•Explain the difference between probable genotypic
and phenotypic ratios and actual numbers of offspring
            This lesson will address Science and
           Technology PA Standards 3.3.10C, and
                        3.2.10C,D
       WHAT IS PROBABILITY?

  Probability is the likelihood
that a particular event will occur

     Example: A coin flip

What are the possible outcomes
    when you flip a coin?

Answer: There are two – it could
   land heads up or tails up
    WHAT IS PROBABILITY? CONT.
  Probability is the likelihood
that a particular event will occur

     Example: A coin flip

What are the chances a coin will
       land heads up?

       Answer: 50% or ½

What are the chances a coin will
        land tails up?

       Answer: 50% or ½
       WHAT IS PROBABILITY? CONT.
If you flip a coin 3 times in a row, what
  is the probability it will land heads up
                 every time?

           Each coin flip is an
 independent event – each time the
   coin is flipped, the probability of it
         landing heads up is ½ .
The probability of flipping 3 heads in a
                  row is:
             ½ x ½ x ½ = 1/8
  Remember: Past outcomes do not
        effect future outcomes!
      HOW DOES PROBABILITY RELATE TO
                GENETICS?
        The principles of probability can be used to
          predict the outcomes of genetic crosses!


                    Coin Toss Lab
•   Work with a partner
•   Click here to practice your probability skills
•   Follow the instructions on this worksheet to
    complete the Coin Toss Lab
          COIN TOSS LAB DISCUSSION
   Did your results equal your calculated
    probabilities?

   What did you notice as your number of tosses
    increased?

Answer: The more times you tossed your coin, the
 closer your actual results should have been to
 your predicted probability.
 Probable outcomes are not always equal to
   actual outcomes; however, the two should
  get closer as the number of trials increases.
             HOMEWORK REVIEW

 When an organism has two identical alleles for a
   particular trait (ex. TT or tt), it is said to be
                      _______.
             Answer: Homozygous

When an organism has two different alleles for the
   same trait (ex. Tt), it is said to be _________.
            Answer: Heterozygous
       HOMEWORK REVIEW CONT.

 This girl is displaying one of the traits from
        your homework – which one?
            Answer: Widow’s Peak

         What is her phenotype?
      Answer: She has a Widow’s Peak

What is a possible genotype given that Widow’s
           Peak is a dominant allele?
              Answer: AA or Aa
      INTERACTIVE ACTIVITY



Click here to practice your
 knowledge of genotype and
 phenotype in this web lab!
             PUNNETT SQUARES
 Let’s combine our knowledge of probability with
  our understanding of genotype and phenotype.




Click on the Punnett Square above to learn how to
    use Punnett Squares to predict the genotypes
   and phenotypes of offspring given the parents’
                    genotypes!
       MORE PUNNETT SQUARES!
Work with a partner to complete this web lab on
               Punnett Squares.

Click on the rooster below to enter the web lab!
                    CLOSURE
  Let’s return to our Bell Ringer…
 What is the genetic disorder that is
       displayed in this picture?
        Answer: Polydactyly

  Polydactyly is a dominant genetic
  disorder. John is heterozygous for
 Polydactyly – What is his genotype?
             Answer: Pp

     What is John’s phenotype?
Answer: He displays the symptoms of
    the disorder – he has six toes.
              CLOSURE CONT.
  John (Pp) marries Diane who is
 homozygous for Polydactyly. What
   are the chances they will have a
     child who is homozygous for
             Polydactyly?
Use a Punnett Square to answer the
              question!
         CLOSURE CONT.
       Answer: 2/4 or 50%
     P      p
P   PP     Pp
P   PP     Pp
                HOMEWORK

    Click on Sponge Bob for a worksheet on
Bikini Bottom Genetics for more Punnett Square
                    practice!