1. Gene Squares

2. Gene Squares
Key Question: How can you predict the probability of traits appearing? Initial Thoughts:

3. Evidence – Punnett Squares
Step by Step 1. Write the possible alleles donated by each parent along the top and left side of the table?
Skye
*Each T along the top represents an allele in the sperm cell produced by Skye. Each t on the left represents an allele in the egg cell from Poppy. TT
T T
Poppy t tt t

4. Evidence – Punnett Squares
Step by Step 2. Complete each box of the table by combining one allele from the top and one allele from the left.
Skye TT
* When you combine one allele from each parent into a box, you are representing a sperm cell fertilizing an egg.
T T Tt
Poppy t tt t

5. Evidence – Punnett Squares
Step by Step
3. Now you can use the Punnett square to make some conclusions.
*All of the offspring of Skye and Poppy will have one allele for blue tail color and one allele for orange tail color. Their genotypes will be Tt. An organism that has alleles for two different traits is called heterozygous. Because blue tail color is dominant over orange, the phenotype of all offspring is blue tails, as found in the breeding experiment between Skye and Poppy.

6. Evidence – Punnett Squares
The cross between the Generation 2 (Tt) critters Ocean and Lucy is: Ocean X Lucy Tt X Tt T = allele for blue tail color (dominant) t = allele for orange tail color (recessive) *Note that while Ocean and Lucy both have blue tails, they are both heterozygous.

7. Evidence – Punnett Squares
Complete this Punnett square for the cross between Ocean and Lucy?
Ocean
a. Place Ocean’s and Lucy’s alleles on the dotted lined in the Punnett square.
b. Complete the Punnett square by filling in each box with the allele above it and the allele to its left. Tt
Lucy
----- Tt
-----

8. Evidence – Punnett Squares
Use either a blue pencil or a regular pencil to shade in the squares for offspring that will have blue tails in your Punnett square.
About what fraction of the offspring of Ocean and Lucy are predicted to have blue tails, according to the Punnett square?
About what fraction are predicted to have orange tails?

9. Analysis Questions
Why is it impossible for offspring to show the recessive trait if one parent is homozygous for the dominant trait?
What is the probability of having a boy (xy) vs. a girl (xx)?
Dad
x y x
Mom x

10. Analysis Questions contd.
A scientist has some purple-flowered pea plants. She wants to find out if the pea plants are homozygous for the purple flower color.
What cross will be best to find out if the purple-flowered peas are homozygous?
Use Punnett squares to show what will happen if the plants are crossed with white-flowered plants and
the purple-flowered plants do not have an allele for the white trait.
the purple-flowered plants do have an allele for the white trait.

11. Summary
What did you think about predicting the probability of traits before?
What did you learn from your evidence about predicting the probability of traits?
What are some further thoughts or questions you have about predicting the probability of traits?

12. Reflection
How can you tell if a flower is homozygous dominant? What experiment can you do?

13. Big Idea