1. Incomplete dominance and co-dominance
Inheritance patterns that are different from that seen in straight dominant-recessive traits

2. Incomplete Dominance
F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Therefore there is a third blended phenotype.
Example: snapdragons (flower colour)
red (RR) x white (R’R’)
RR = red flower
R’R’= white flower R R’

3. Incomplete Dominance R produces the RR’ F1 generation All RR’ = pink
(heterozygous individuals
display an intermediate
phenotype - pink.)
produces the
F1 generation
RR’

4. Codominance
Two alleles are expressed (multiple alleles) in heterozygous individuals.
Example – petunia flowers can show codominance
If a purple flowered petunia is crossed with a white flowered petunia, purple and white flowered offspring will result.

5. Petunia cross Purple petunia (PP) x white petunia (WW) P P W
All PW = purple and
white (heterozygous
individuals display
both phenotypes)
produces the
F1 generation PW PW PW PW

6. Blood type in humans is an example of a codominant trait
1. type A = IAIA (AA) or IAi (AO)
2. type B = IBIB (BB) or IBi (BO)
3. type AB = IAIB (AB)
4. type O = ii (OO)

7. Codominance IB IAIB IA IBi i Example: homozygous male B (IBIB) x
heterozygous female A (IAi) IA IB i
IAIB
IBi
1/2 = IAIB
1/2 = IBi

8. Codominance Example: male O (ii) x female AB (IAIB) i IA IB IAi IBi

9. Codominance
Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents.
boy - type O (ii) X girl - type AB (IAIB)

10. Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi
phenotypes = A and B

11. Answer Questions # 1-6 on page 244