Download presentation
Presentation is loading. Please wait.
Published byRebecca Hart Modified over 8 years ago
1
Punnett Squares
2
Are traits and variations equally shown? Are all traits and their variations equally shown in organisms? Why not? If your mom has blue eyes and your dad has brown eyes, does the offspring have 1 blue eye and 1 brown eye? How is it decided which trait you get?
3
Punnett Square Has anyone ever heard of a Punnett Square? What does it do? A Punnett Square is a way to look at the traits of two parents and predict what trait the organism will have. We are going to explore Punnett Squares with the trait of eye color
4
Symbols for traits When scientists look at traits inside a Punnett Square, there is a specific way to write the trait. A trait for is written with one letter, and the letter could be uppercase or lowercase. But if you look at a trait for an organism, the each trait always has 2 letter. For example, the trait for tasting PTC may be shown with a P. But when looking at a person, their trait would be Pp, PP, or pp. Why do you think one trait has 2 letters?
5
For this activity, the trait of eye color will be represented by a B. So organisms can have BB, Bb, or bb when representing their eye color trait To set up a Punnett square, you write the 2 letters for Dad’s trait on top of each square Then you write the 2 letters for Mom’s trait to the left of each square Finally, you bring whatever letters are outside the square inside the square Let’s do scenario one is the packet together. The dad is BB and the mom is bb.
6
Now that you have the correct letters inside the Punnett square, look at the plastic bag you each have. There are brown and blue squares. Each color of square has either a B or b on them. For each letter on your Punnett Square, I want you to place the colored square on top of the letter than matches the letter on the Punnett Square.
7
After you have one colored square for each letter on your Punnett Square, I want you to place the squares on top on one another for each trait. For example, the for two letters that go together for Dad’s trait, those 2 colored squares should be put on top of one another. Are there any questions?
8
Answer the questions below scenario 1 that we completed together. Now try the next scenarios on your own. Remember: To set up a Punnett square, you write the 2 letters for Dad’s trait on top of each square Then you write the 2 letters for Mom’s trait to the left of each square Finally, you bring whatever letters are outside the square inside the square Answer the questions below each scenario
10
Making Sense Now answer the Making Sense questions on your packet What trait do you think is dominant? What evidence do you have to support this? What trait do you think is recessive? What evidence do you have to support this? What happened when you put the blue and brown squares on top of one another?
11
Making Sense What do the four squares inside the Punnett Square represent? So does this mean that every parent is going to have 4 offspring? The four squares represent the chance, or probability of what trait their offspring will have. If in a Punnett square, there are 3 brown squares, and 1 blue square, what is the chance of having a child with blue eyes? Fill in the chart below the Making Sense questions
12
Homozygous and Heterozygous Who knows what homozygous means? Here is a hint. The root word “homo” means same in Greek. So looking at scenario 1 on our worksheet, do you think either parent is homozygous for a trait? What about heterozygous? The root word hetero in Greek means different. So now let’s look at scenario 2 in our worksheet. Are any of those parents heterozygous for their trait?
13
Homozygous and Heterozygous Homozygous means having 2 of the same letters in the trait. It means that trait is homozygous. Heterozygous means each letter is different for a trait On the notes section of the worksheet, copy down the definition of homozygous and heterozygous
14
Recessive vs. Dominant We said earlier that brown eyes was the dominant trait. If you had to define dominant trait, what would it be? What about recessive trait? So when writing dominant traits the letters are always capitalized. Recessive traits, the letters are always lowercase. Write the definitions of dominance and recessive in your notes.
15
Bringing it All Together Now let’s combine these terms. On your packet there is a table. For each parent in each situation, you are going to write them in where they below. So if the mom in scenario 1 is heterozygous dominant, under heterozygous dominant you will write scenario 1- mom.
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.