1. 11.2 Probability and Punnett Squares

2. Probability
The likelihood that a particular event will occur is probability

3. Probability Example: flipping a coin
50% chance you will get heads, 50% chance you will get tails
Also called a 1 in 2 chance (1/2)

4. Probability
IMPORTANT: Each event does not effect the event before or the event after
You have EXACTLY the same probability each time

5. Probability of Many Events
Multiply the probabilities for each flip.
Example: if you want to see what your probability is to get heads 3 times in a row, you would calculate (½) x (½) x (½) = 1/8

6. Probability and Genetics
The principles of probability can be used to predict the outcomes of genetic crosses.
Example: predict the offspring of a cross between two individuals.

7. Probability Activity State the question and hypothesis.
Answer the pre-activity questions together as a class.
Flip a coin 100 times.
Record how many times the coin landed on heads and how many times the coin landed on tails.
Calculate the frequency (totals) of heads and tails.
Calculate the percentage of heads and tails.
Answer the post-lab questions.

8. Probability Worksheet
Things to remember:
One event does NOT effect a later event
Probability of multiple events, you must multiply each probability

9. Punnett Squares

10. 1. Punnett Squares
Diagram used to determine the results of a genetic cross

11. Punnett Squares Genes have two different possibilities
Two different alleles
These alleles separate during gamete formation (segregation)

12. 2. Terminology
Dominant Allele: the trait that will always be seen if it is present
It is “stronger” than the recessive trait
Represented by a capitol letter

13. Terminology
Recessive Allele: the trait that will only be seen if a dominant allele is not present
Overpowered by dominant alleles
Represented by a lower case letter

14. Phenotype and Genotype
Physical characteristics
Example: hair color, height, eye color
Genotype
Genetic makeup

15. Phenotypes and Genotypes
Important: Some individuals may have the same phenotype with different genotypes
Example: Aa will look like AA
Same phenotype but different genotypes!

16. Terminology Homozygous: two identical alleles for a trait
Also called “pure”
“homo-” means “same”

17. Terminology Heterozygous: two different alleles for a trait
Considered “hybrid” for that trait
“hetero-” means “different”

18. Dominant and Recessive
Homozygous dominant: two dominant alleles
Will show the dominant trait
Example: AA
Homozygous recessive: two recessive alleles
Will show the recessive trait
Example: aa
Heterozygous
One dominant and one recessive allele
Example: Aa

19. Practice with Genetics Terminology
Get a piece of paper.
Cut the paper into 4 sheets.
On each sheet write:
Two sheets with a capitol A
Two sheets with a lower case a
Terms: Heterozygous, Homozygous, Homozygous recessive, Homozygous dominant

20. Punnett Squares

21. 1. Baby Steps Through the Punnett Square
Determine the genotypes of the parents
Write down your cross
Draw a punnett square
Split the letters of the genotype for each parent and put them outside the punnett square
Fill in the punnett square to determine the genotypes of the offspring
Summarize – percentages of genotypes and phenotypes (these may be different percentages!)
Keep on practicing!

22. Making Babies!
This activity involves using the terms we just learned in order to create an individual with each trait.
Once you have gotten each trait, you will draw your baby.
Yes, you may name it!