1. Incomplete Dominance Codominance Multiple Alleles
In a nutshell!
HW: Complete the HW
Packet (by Monday)
Resubmission of genetics Quiz 2 by Monday

2. Review: Dominant/Recessive
One allele is dominant over the other (capable of masking the recessive allele)
PP = purple
Pp = purple
pp = white

3. Review Problem: Dominant/Recessive
In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants.
P p
GENOTYPES:
- PP (1); Pp (2); pp (1)
- ratio 1:2:1 P p PP Pp
PHENOTYPES: Pp pp
- purple (3); white (1)
- ratio 3:1

4. Incomplete Dominance
A third (new) phenotype appears in the heterozygous condition.
RR = red
rr = white
Rr = pink

5. Problem: Incomplete Dominance
Show the cross between a red and a white flower.
GENOTYPES:
R r
- RR (1); Rr (2);
rr (1)
- ratio 1:2:1 R r Rr rr RR
PHENOTYPES:
Red (1); Pink (2);
white (1)
- ratio 1:2:1

6. Problem: Incomplete Dominance
Show the cross between a pink and a white flower.
GENOTYPES:
R r
- Rr (2); rr (2)
- ratio 1:1 r rr Rr
PHENOTYPES:
- pink (2); white (2)
- ratio 1:1

8. Codominance
The heterozygous condition, both alleles are expressed equally
Sickle Cell Anemia in Humans
SS = sickle cells
NN = normal cells
NS = some of each
sick

9. What do you notice about the letters N and S in the Genotypes of F1?
Sickle cell anemia
Problem: Codominance
Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick.
N S
GENOTYPES:
- NS (2) SS (2)
- ratio 1:1 S NS SS
PHENOTYPES:
- carrier (2); sick (2)
- ratio 1:1
What do you notice about the letters N and S in the Genotypes of F1?

10. How Do We Determine If a Trait IS
Dominant/Recessive
Incomplete Dominance
Co-Dominance Rr RW
Look at the Phenotype of the
HETEROZYGOUS offspring

11. Multiple Alleles
Sometimes there are more than two alleles for a trait – can you think of any?
Blood type in humans
Blood Types?
Type A, Type B, Type AB, Type O
Blood Alleles?
A, B, O (often expressed – IA, IB, I)

13. Rules for Blood Type A and B are codominant
AA = Type A
BB = Type B
AB = Type AB
A and B are dominant over o
Ao = type A
Bo = type B
oo = type O

14. Problem: Multiple Alleles
Show the cross between a mother who has type O blood and a father who has type AB blood.
Io Io
GENOTYPES:
IA Io (2) IB Io (2)
- ratio 1:1 IA IB
IA Io
IB Io
PHENOTYPES:
- type A (2); type B (2)
- ratio 1:1
What do you notice about the letters N and S in the Genotypes of F1?

15. Blood Type – Two Ways to Write It

16. In Cases of CO-Dominance
Both alleles are expressed in the heterozygote and both take a CAPITAL CASE letter
An index letter may identify the allele
Therefore (Blood):
Normal haemoglobin allele is also HbN
Sickle cell allele is also HbS

17. Comprehension Questions
ROAN CATTLE
Red Hair (RR)
White (WW)
HETEROZYGOUS =
Is this
A: Codominance
B: Incomplete Dominance
What color is the Heterozygous Offspring?

18. BIRD WINGS White Wings (WW) Blue Wings (BB) Heterozygous =
What gives it away that it is CO-Dominance?

19. Rose Color Red Rose (RR) White Rose (ww) Heterozygous = Is this
A: Codominance
B: Incomplete Dominance
What gives it away that it is Incomplete-Dominance?

20. Human Skin Color Incomplete dominance Controlled by 4 to 6 genes!!!
(Take Away – ONE CHARACTERISTIC MAY BE CONTROLLED BY MULTIPLE GENES!)