Presentation on theme: "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."— Presentation transcript:
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 Tt T t Dominant AllelesRecessive Alleles
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?