1. Co-dominance, Incomplete Dominance
Catalyst
The talkative allele is dominant to quiet.
Create a Punnett square showing potential offspring from a heterozygous father and homozygous recessive mother.
List the percentages for genotype AND phenotype
Write in complete sentences!
Don’t talk during the Catalyst!

2. By the end of today, SWBAT…
Objectives
By the end of today, SWBAT…
Create and analyze Punnett Squares for co-dominant and incompletely dominant alleles.

3. Catalyst Review Talkative = _____ Quiet = _____ Father = _____ _____
Mother = _____ _____
Homozygous dominant = _____ %
Homozygous recessive = _____ %
Heterozygous = _____ %
Fill in on Promethean

4. If You’re Confused About Percents…
Each square is one quarter of the whole
What percent of the offspring will be homozygous dominant?
What percent of the offspring will be homozygous recessive?
What percent of the offspring will be heterozygous?
What percent of the offspring will show the dominant trait?
What percent of the offspring will show the recessive trait? A a A AA Aa
50 cents = 50%
0 cents = 0%
50 cents = 50% A AA Aa
100 cents = 100%
0 cents = 0%

5. Review: Dominant/Recessive
A dominant allele is capable of masking, or covering up, a recessive allele.
PP = purple
Pp = purple
pp = white
This slide hidden. Not strictly necessary. But if you think your students could use some more practice, un-hide it.

6. Review: Dominant/Recessive
In pea plants, purple flowers (P) are dominant over white flowers (p). Show the potential offspring between two heterozygous plants.
P p
GENOTYPES: P p PP Pp
PP: 25%
Pp: 50%
pp: 25%
This slide hidden. Not strictly necessary. But if you think your students could use some more practice, un-hide it. Pp pp
PHENOTYPES:
Purple: 75%
White: 25%

7. Incomplete Dominance Key Point #1:
In incomplete dominance, one allele does not mask the other. In heterozygotes, the phenotype is IN BETWEEN dominant and recessive.
Example: In snapdragon flowers, red (R) and white (r) are incompletely dominant.
During this slide, early finishers should get whiteboards + markers for their tables.

8. Incomplete Dominance r R R R R r R R r r r r

9. Guided Practice (GP) 1 GENOTYPES: PHENOTYPES:
In humans, being tall (T) and short (t) is incompletely dominant.
Show the potential offspring of a heterozygous father and a homozygous recessive mother.
Fill in percents for genotype and phenotypes.
GENOTYPES:
TT:
Tt:
tt:
Fill in on Promethean.
PHENOTYPES:
Tall:
Short:
Medium:

10. Guided Practice (GP) 2 GENOTYPES: PHENOTYPES:
In African-Americans, dark skin (D) and light skin (d) are incompletely dominant.
Show the potential offspring of a homozygous dominant father and a homozygous recessive mother.
Fill in percents for genotype and phenotype.
GENOTYPES:
Fill in on Promethean.
PHENOTYPES:

11. Guided Practice (GP) 3 GENOTYPES: PHENOTYPES:
In dragons, long tails (L) and short tails (l) are incompletely dominant.
Show the potential offspring of a homozygous recessive father and a heterozygous mother.
Fill in percents for genotype and phenotype.
GENOTYPES:
Fill in on Promethean.
PHENOTYPES:

12. Co-Dominance AA = normal cells SS = sickle cells AS = half of each
Key Point #2:
In co-dominance, both alleles are dominant. In heterozygotes, both alleles are expressed EQUALLY.
Example: Sick cell anemia in humans
AA = normal cells
SS = sickle cells
AS = half of each

13. Sickle Cell Anemia

14. Sickle cells easily get stuck in the circulatory system.

16. Why would African Americans be so much more likely to have Sickle Cell anemia?

18. The story gets more interesting
People who are AA get malaria and die.
People who are SS have decreased life expectancy.
People who are AS are resistant to malaria!!!
Having some sickled cells hurts them, but the benefit outweighs the cost

19. Sickle Cell Anemia A S A A AA AA AS AS GENOTYPES: PHENOTYPES: AA: 50%
Being normal (A) and having sickle cell anemia (S) are co-dominant.
Show the potential offspring of a normal father and a heterozygous mother.
Fill in percents for genotype and phenotype.
A A
GENOTYPES:
AA: 50%
AS: 50%
SS: 0% A S AA AA
PHENOTYPES: AS AS
Normal: 50%
Some normal, some sickle: 50%
Sickle Cell: 0%

20. GP 4 GENOTYPES: PHENOTYPES:
Being normal (A) and having sickle cell anemia (S) are co- dominant.
Show the potential offspring of two heterozygous people.
Fill in percents for genotype and phenotype.
GENOTYPES:
AA:
AS:
SS:
PHENOTYPES:
Normal:
Some normal, some sickle:
Sickle Cell:

21. GP 5 GENOTYPES: PHENOTYPES:
In cows, color is co-dominant. Show the potential offspring between a white bull (WW) and a red cow (RR).
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:

23. GP 6 GENOTYPES: PHENOTYPES:
In dragons, teeth can either be long (L) or sharp (S). Show the potential offspring between a heterozygous dragon, and a dragon that is homozygous for sharp teeth.
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:

24. Blood Typing
Sometimes there are more than two alleles for a trait. The most important one for you to learn about is… blood type!
Key Point #3:
Blood type has three alleles: IA, IB, and i.
IA and IB are co-dominant.
i is recessive.
Before KP#3, ask students if they know their blood type.

25. Blood Types IA and IB are co-dominant i is recessive IA IA = Type A
IB IB = Type B
IA IB = Type AB
i is recessive
IA i = Type A
IB i = Type B
i i = Type O

26. Blood Typing IB IA i IAIB IB i IA i i i GENOTYPES: i PHENOTYPES:
Show the potential offspring between a mother who is heterozygous for Type A blood and a father who is heterozygous for Type B blood.
IA i
GENOTYPES: IB i
IAi: 25%
IBi: 25%
IAIB: 25%
ii: 25%
IAIB
IB i
IA i
i i
PHENOTYPES:
Type A: 25%
Type B: 25%
Type AB: 25%
Type O: 25%

27. GP 5 GENOTYPES: PHENOTYPES:
Show the potential offspring between a father who is homozygous for Type A blood and a mother who is homozygous for Type B blood.
GENOTYPES:
Fill in on Promethean board.
PHENOTYPES:

28. GP 6 GENOTYPES: PHENOTYPES:
Show the potential offspring between a mother who is Type O blood and a father who is Type AB blood.
GENOTYPES:
Fill in on Promethean board.
PHENOTYPES:

29. Conclusion Incomplete dominance: Co-dominance:
Heterozygotes are a BLEND of the two alleles.
Example: pink snapdragon flowers
Co-dominance:
Heterozygotes show BOTH alleles EQUALLY.
Example: sickle cell trait, roan cows

30. Exit Question
In Mr. LY’s students, raising your hand (R) and shouting out answers (r) is INCOMPLETELY DOMINANT. Angelina is heterozygous, and Jaron is homozygous recessive.
Create a Punnett square showing potential offspring.
List the percent probability of each genotype AND phenotype
Write in complete sentences!
Don’t talk during the Exit Question!