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 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?

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

Punnett Square Diagram Dominant Alleles Recessive Alleles T t

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

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

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

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

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.

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!

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?

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?