1. Dominant, Recessive, Heterozygous, Homozygous
Catalyst:
Toby has a deep voice.
Is this genotype or phenotype?
HOW DO YOU KNOW?
Paula has one allele for being tall, and one allele for being short.
Write in complete sentences!
Don’t talk during the Catalyst!

2. Objectives By the end of today, all SWBAT…
Differentiate between homozygous and heterozygous genotypes
Determine the phenotype of an organism, based on its genotype

3. Quick Review All living organisms have two alleles for every gene
Gene controls one trait
Allele = version of a gene
Genotype = which alleles you got from parents
Phenotype = physical expression of the genotype
This could be the gene for anything; it doesn’t matter. Ask them where did they get the top and the bottom. Could get different all

4. New Vocabulary
Key Point #1: Genotypes are either heterozygous or homozygous.
What do you think these words mean?
Homo = “same”
Hetero = “different”
Homozygous = two of the SAME alleles
Heterozygous = two DIFFERENT alleles
Examples
Tierra has two alleles for brown eyes. She is homozygous for eye color.
Reginald has one allele for green eyes, and one allele for brown eyes. He is heterozygous for eye color.
Stress importance of this vocabulary

5. Check for Understanding (CFU)
Michael has one allele for a widows peak, and one allele for a straight hairline.
Homozygous or heterozygous for hairline shape?

6. Check for Understanding (CFU)
Adam has two alleles for curly hair.
Homozygous or heterozygous for hair type?

7. Check for Understanding (CFU)
Byron has two alleles for hairy forearms.
Homozygous or heterozygous for amount of forearm hair?

8. Check for Understanding (CFU)
Jordan has one allele for straight hair, and one allele for wavy hair.
Homozygous or heterozygous for hair type?

9. Principle of Dominance
The two types of alleles are dominant and recessive.
Key Point #2: If an organism is heterozygous, a dominant allele will mask the recessive allele.
Example: hair color (gene)
The brown allele is dominant, the blonde allele is recessive
Yashira has two blonde alleles. Her hair color is blonde.
Melvin has two brown alleles. His hair is brown.
Jelisa has one brown allele and one blonde allele. Her hair is BROWN!!!

10. Check for Understanding (CFU)
Long fingers is dominant, short fingers is recessive
Aisha has two dominant alleles
What type of fingers does she have?

11. Check for Understanding (CFU)
Long fingers is dominant, short fingers is recessive
Ros’Joan has one dominant allele and one recessive allele
What type of fingers does she have?

12. Check for Understanding (CFU)
Long fingers is dominant, short fingers is recessive
Dweldon has two recessive alleles
What type of fingers does he have?

13. Check for Understanding (CFU)
Long fingers is dominant, short fingers is recessive
Kody has one dominant allele and one recessive allele
What type of fingers does he have?

14. But Mr. J, I’m Lazy! Let’s abbreviate things.
Key Point #3: There are three rules for abbreviating genotype
Dominant allele = capital letter
Recessive allele = lowercase letter
BOTH alleles use the first letter of the dominant trait
Long tails in dogs are dominant, short tails are recessive
Long = L
Short = l

15. Dominant and Recessive Genotypes
For every gene you have two alleles, and each of those could be dominant or recessive.
So a dog could have THREE different GENOTYPES for tail length:
LL (homozygous dominant)
Ll (heterozygous)
ll (homozygous recessive)

16. Dominant and Recessive Phenotypes
But dogs could only have two different tail lengths.
Remember that a dominant allele will mask a recessive one. So for this genotype you get….
LL (long tail)
Ll (long tail)
ll (short tail)

17. Let’s Practice More T, t Tt Tall Tall
Pea plants can have two alleles for the gene for height: tall and short. Tall is dominant to short.
What letters would represent the two alleles?
What would be the genotype of a heterozygous flower?
What would be the phenotype of a flower with TT?
What would be the phenotype of a flower with Tt?
T, t Tt
Walk them through the example problem. They will try to do T and S. Make sure that they DON’T
Tall
Tall

18. Whiteboard Practice!
Add your direcdtions here

19. Guided Practice
Hitchhiker’s thumb is a trait in humans. Normal thumbs are dominant to Hitchhiker’s thumb. Using the letter “H,” show an individual who is homozygous recessive for the gene for hitchhiker’s thumb.
What is this person’s phenotype?
Write the genotype for someone heterozygous.

20. Guided Practice
The bunnies of the forests of Louisiana can either be brown or black. Brown is dominant to black.
Write all the genotypes possible for a brown bunny.
What would the phenotype be for a bunny with the genotype of Bb?
What would be the phenotype of a bunny with the genotype of BB?

21. Guided Practice
People can have either free or attached earlobes. Free is dominant to attached.
What letters would you use to represent the alleles?
What genotype is someone who is Ff?
What phenotype is someone who is ff?
What phenotype is someone who is homozygous dominant?

22. Guided Practice
Chickpeas can be either green or yellow. Yellow is dominant to green.
What is the genotype of a green pea? Explain.
What is the genotype of a yellow pea? Explain.
What is phenotype of a pea plant that is YY?
What is the phenotype of a heterozygous pea plant?
This is our synthesis slide. If they get it, they should get it, if not then you know they may have a few problems left to work out.

23. Independent Practice (IP)

24. Key Point Wrap-Up
Key Point #1: Genotypes are either heterozygous or homozygous.
Homozygous = two of the SAME alleles
Heterozygous = two DIFFERENT alleles
Key Point #2: If an organism is heterozygous, a dominant allele will mask the recessive allele.
Key Point #3: There are three rules for abbreviating genotype
Dominant allele = capital letter
Recessive allele = lowercase letter
BOTH alleles use the first letter of the dominant trait

25. Exit Question
The gene for fur color in mice has alleles for brown and white. Brown is dominant to white.
What letters are used for the alleles?
Write the genotype AND phenotype for a mouse that is homozygous recessive.
Write in complete sentences!
Don’t talk during the Exit Question!