1. Incomplete Dominance and Codominance
Thursday, October 20, 2011

2. Simple Dominance
Dominant: An organism with a dominant allele for a trait will ALWAYS have that trait.

3. Simple Dominance
Dominant: An organism with a dominant allele for a trait will ALWAYS have that trait.
Recessive: An organism with a recessive allele for a trait will only show that form when the organism is homozygous recessive (has 2 recessive alleles).

4. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth

5. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
Which allele is dominant, warty or smooth?

6. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
Which allele is recessive, warty or smooth?

7. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
What is the genotype of a pumpkin that is homozygous recessive?

8. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
What is the genotype of a pumpkin that is heterozygous for pumpkin shape?

9. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
What is the phenotype of a pumpkin that has the genotype WW?

10. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
What is the phenotype of a pumpkin that has the genotype Ww?

11. Examples of Simple Dominance
Pumpkin shape: W = warty w = smooth
What is the phenotype of a pumpkin that has the genotype ww?

12. Examples of Simple DominanceW w w w

13. Examples of Simple DominanceW w w Ww ww Ww ww w

14. Examples of Simple Dominance
What is the probability that these two pumpkins will have a warty baby pumpkin? W w w Ww ww Ww ww w

15. Examples of Simple Dominance
What is the probability that these two pumpkins will have a warty baby pumpkin? W w w Ww ww
75% Ww ww w

16. Simple dominance is not the whole story…
Some alleles are neither DOMINANT or RECESSIVE and some traits are controlled by multiple alleles or multiple genes.

17. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. Think blend in.

18. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. Think blend in
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.

19. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We use two capital letters, since neither letter is completely dominant or completely recessive.

20. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We use two capital letters, since neither letter is completely dominant or completely recessive.
Example: Blending colors.

21. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We usually use two capital letters, since neither letter is completely dominant or completely recessive.
Example: Blending colors.
W = white petals
R = red petals RR WW

22. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We usually use two capital letters, since neither letter is completely dominant or completely recessive.
Example: Blending colors.
WW = white petals
RR = red petals
WR = pink petals
WR or RW

23. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We usually use two capital letters, since neither letter is completely dominant or completely recessive.
Example: Blending colors.
Note: Testmakers sometimes use one letter instead of two! RR ww Rr

24. Simple dominance is not the whole story…
INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other.
The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.
We usually use two capital letters, since neither letter is completely dominant or completely recessive.
Example: Blending colors.
Note: Testmakers sometimes use one letter instead of two!
The trick is to see if the heterozygous genotype has a “new” blended phenotype. RR ww Rr

25. Let’s practice!

26. Simple dominance is not the whole story…
CODOMINANCE: When both alleles show up (neither allele is recessive). Think together.

27. Simple dominance is not the whole story…
CODOMINANCE: When both alleles affect the phenotype (appearance).
Example: Spots of both colors, blood type, sickle cell disease.

28. Codominance
RR = red
WW = white
RW or WR = red and white spotted