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Section 11-2: Probability and Punnett Squares

Section 11-2: Probability and Punnett Squares. 1. Probability. The likelihood that a particular event will happen For example: A Coin Toss 2. A coin has a 50% chance to be heads or tails 3. Is the outcome of the flip determinant on past flips? No!. Probability and Genetics.

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Section 11-2: Probability and Punnett Squares

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  1. Section 11-2: Probability and Punnett Squares

  2. 1. Probability • The likelihood that a particular event will happen • For example: A Coin Toss • 2. A coin has a 50% chance to be heads or tails • 3. Is the outcome of the flip determinant on past flips? • No!

  3. Probability and Genetics • How does probability effect genetics? • The Segregation of Alleles • 4. When alleles segregate it is completely random, very similar to a coin toss. • Interesting to think of how things could have been different don’t you think?

  4. The Punnett Square • 5. Allows possible gene combinations to be predicted by the use of a diagram • Can be used to predict and compare genetic variations that will result from a cross • As well as the probability of occurance

  5. Punnett Square Diagram Dominant Alleles Recessive Alleles

  6. 8. Homozygous • Having two identical alleles for a particular trait • Ex: TT or tt • “True-Breeding” for • a Particular Trait • Examples: • Hydras • Mushrooms • Bacteria

  7. 10. Heterozygous • Organisms having two different alleles for the same trait • Ex: Tt • “Hybrids” for a particular trait • Examples: • Cross Pollinating Plants • Mules • The majority of higher • organisms

  8. 9. Phenotype • The physical characteristics of an organism • In our Punnett Square example what are our phenotypes? • Tall • TT or Tt • Short • tt

  9. 7. Genotype • The genetic makeup of an organism • In our Punnett Square example what would the genotypes be? • TT- 25% • Tt- 50% • tt- 25%

  10. Phenotype VS Genotype: Plant 1: Homozygous (TT) Plant 2: Heterozygous (Tt) 12. Just because an organism has the same phenotype, that doesn’t mean it always has the same genotype.

  11. 13.Probability and Segregation • Let’s look at our Hybrid Cross results: • 14. Mendel’s Requirements for Segregation • ¾ of plants displayed the Tall phenotype • ¼ of plants displayed the Short phenotype • 3:1 ratio of tall to short plants • Did Segregation occur in relation to Mendel’s model? • YES!

  12. Probabilities Predicting Averages • 15.Probabilities predict the average outcome of large scale events, BUT not precise individual events • 16. For example: Coin Toss • You can get 50:50 ratio but it could take you numerous tosses • Are the odds in our favor for just 2 tosses?

  13. Probabilities Predicting Averages • 17. The larger the number of offspring in a genetic cross, the better chances that the values will show the 3:1 ratio. • 18. So which would offer the better data? • An F1 generation of 100? • An F1 generation of 1000?

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