1. Probability of Inheritance Lesson 2
Mrs. Anna Ward
Seventh Grade Science
Ridge Road MS

2. DO NOW!!!!
Copy down this diagram in your notes!!!!

3. Agenda Review from yesterday. What is a Punnett Square?
Why do we use them?
What can they tell me?
How to do a Punnett Square
Six Steps to Success
Discovery Ed video
Think, Pair, & Share Practice

4. Punnett Square…What are they and why do we use them?
A Punnett Square is a chart used to show the possible ways genes from two parents can combine in order to predict possible genotypes of offspring
Punnett Squares also help us determine the probability and ratios of these offspring.

5. Punnett Squares— STEP ONE
Identify the Genotypes of Each Parent!
In this case:
TT and tt

6. PUNNETT SQUARES STEP TWO
DRAW A BOX WITH A CROSS.

7. Punnett Squares— STEP THREE
Add the Genotype information from One parent across the top.
Add the Genotype information from the other parent down the side.
TT x tt t t

8. Punnett Squares— STEP FOUR
Add the Alleles from One Parent to the Punnett Square.
TT x tt T T t t T T

9. Punnett Squares— STEP FIVE
Add the Alleles from the other Parent to the Punnett Square.
TT x tt t T t T t t T t T t

10. Punnett Squares— STEP SIX Calculate the Results
The final result of crossing a Pea Plant (TT) with a Pea Plant (tt) is that all the offspring will have the GENOTYPE “Tt”.
CFU: If all the genotypes are “Tt” what is the phenotype? (Are they tall or short?)

11. However, if those two plants are crossed…
What Happens???
Remember step one…IDENTIFY THE PARENT GENOTYPES!
Tt x Tt

12. STEP 2
Draw the Box with a cross.

13. STEP 3 T t
Add in the Genotypes of the parents across the top and down the side.
Tt x Tt T t

14. STEP 4 T t
Add the alleles from one parent into the Punnett Square
Tt x Tt T T t t T t

15. STEP 5 T t
Add the alleles from the other parent into the Punnett Square
Tt x Tt T T T T t t T t t t
NOTE: When writing genotypes, the DOMINANT allele ALWAYS comes first!!!!!

16. Step 6—Calculate the Final Results..
When crossing two plants with a Tt genotype we get…
One plant with the genotype TT
Two plants with the genotype Tt
One plant with the genotype tt

17. Checking for Understanding…
What are the phenotypes for the Genotypes of this Punnett Square?
One plant with the genotype TT
Two plants with the genotype Tt
One plant with the genotype tt
TALL
TALL
Short
In other words, we get three tall plants for every one short plant.

18. Discovery Ed Video to help explain….
E A E3BB24

19. Punnett Squares
The type of Punnett Squares we are doing are MONOHYBRID CROSSES.
Monohybrid Crosses are used to evaluate the potential genotypes of offspring when looking at traits that are determined by a single allele.
You will need to know the steps for completing a Monohybrid Cross (or Punnett Square).
Glue in the Punnett Square Cheat Sheets into your science notebook.

20. Now it is time for you to practice…
What would the result of crossing a Heterozygous Tall pea plant (Tt) with a homozygous Tall pea plant?
What would be the result of crossing a homozygous Short pea plant (tt) with a homozygous Short pea plant (tt)?
What would be the result of crossing a heterozygous Tall (Tt) pea plant with a homozygous Short pea plant?
What would be the result of crossing a heterozygous tall pea plant with a heterozygous tall pea plant?

21. Exit Ticket… Which of the following is a heterozygous genotype?Aa BB cc DD
What is another name for the type of Punnett Squares we are completing?
What would happen if I cross a HOMOZYGOUS DOMINANT Brown Haired Woman (BB) with a HOMOZYGOUS RECESSIVE Blond Haired Man?