Mrs. Anna WardSeventh Grade ScienceJames Martin MS

PROBABILITY OF INHERITANCE LESSON 2

DO NOW!!!!• Copy down this diagram in your notes!!!!

Announcements• Short Quiz tomorrow to check for understanding

• Notebook Exemplars• Don’t abuse this resource• You MUST do your work IN CLASS. I will remove the notebooks

as well as the information from my WIKI if I feel you are not working in class!

Please continue all of your HARD WORK!!!!

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

Punnett Square…What are they and why do we use them?

•A Punnett Square is a tool that we use to help determine the potential offspring of two parent organisms.

•Punnett Squares also help us determine the probability and ratios of these offspring.

Punnett Squares—STEP ONE

Identify the Genotypes of Each Parent!

In this case:

TT and tt

PUNNETT SQUARESSTEP TWO

DRAW A BOX WITH A CROSS.

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

t

t

Punnett Squares—STEP FOUR

Add the Alleles from One Parent to the Punnett Square.

TT x tt

T T

t

tT

T

T

T

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

tt

tt

Punnett Squares—STEP SIXCalculate 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?)

However, if those two plants are crossed…

What Happens???

Remember step one…IDENTIFY THE PARENT GENOTYPES!

Tt x Tt

STEP 2Draw the Box with a cross.

STEP 3Add in the Genotypes of the parents across the top and down the side.

Tt x Tt

T

t

t

T

STEP 4Add the alleles from one parent into the Punnett Square

Tt x Tt

T

t

t

T

T

T

t

t

STEP 5Add the alleles from the other parent into the Punnett Square

Tt x Tt

T

t

t

T

T

T

t

tT T

tt

NOTE: When writing genotypes, the DOMINANT allele ALWAYS comes first!!!!!

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

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.

Discovery Ed Video to help explain….

• http://player.discoveryeducation.com/index.cfm?guidAssetId=AB33E612-2755-4901-8A44-857151E3BB24

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.

Now it is time for you to practice…1. What would the result of crossing a Heterozygous Tall

pea plant (Tt) with a homozygous Tall pea plant?

2. What would be the result of crossing a homozygous Short pea plant (tt) with a homozygous Short pea plant (tt)?

3. What would be the result of crossing a heterozygous Tall (Tt) pea plant with a homozygous Short pea plant?

4. What would be the result of crossing a heterozygous tall pea plant with a heterozygous tall pea plant?

Exit Ticket…1. Which of the following is a heterozygous genotype?

a. Aa

b. BB

c. cc

d. DD

2. What is another name for the type of Punnett Squares we are completing?

3. What would happen if I cross a HOMOZYGOUS DOMINANT Brown Haired Woman (BB) with a HOMOZYGOUS RECESSIVE Blond Haired Man?