Dominant, Recessive, Heterozygous, Homozygous

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. • Is this genotype or phenotype? • HOW DO YOU KNOW? 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

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.

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 THREEdifferent 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 • 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 Tall Tall

18. Whiteboard Practice!

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. • What is this person’s phenotype?

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?

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!