1. Looking at incomplete and codominance
Monohybrid Crosses
Looking at incomplete and codominance

2. Incomplete Dominance
The dominant allele can’t completely hide the recessive allele, so a heterozygous genotype results in a phenotype that is a mix of the other 2 phenotypes

3. Example 1
In some plants, red (R) flower color is incompletely dominant over white (r) color. Show the cross between two plants heterozygous for flower color.
R r R r
G = RR, Rr, rr GR = 1:2:1
P = red, pink, white PR = 1:2:1 RR Rr rr

4. Example 2
Show the cross between a homozygous dominant and a heterozygous plant.
R R R r
G = RR, Rr GR = 2:2:0
P = red, pink PR = 2:2:0 RR Rr

5. Codominance
Occurs when both alleles for a gene are expressed in a heterozygous offspring
No allele is dominant or recessive

6. Example 1
In horses, red coat is codominant with white coat. Show the cross between a red (R) horse and a white horse (R’).
R R R’
G = RR’ P = Roan GR = 0 (RR): 4 (RR’): 0 (R’R’) PR = 0:4:0
RR’

7. Example 2 Show the cross between a white horse and a roan horse. R’ R’
G = RR’, R’R’ P = roan, white GR = 0:2: PR = 0:2:2
RR’
R’R’