- Where both alleles are equally dominant
- Therefore, both alleles are expressed in the phenotype
e.g. Snapdragon plant has one allele codes for enzyme which catalyses formation of red pigment and other allele codes for enzyme that lacks this catalytic activity
If alleles showed the usual pattern of 1 dominant and 1 recessive the flower would be either red and white
But as they are co-dominant three colours of flower are found:
Homozygous (1st allele): Both alleles code forthe enzyme and so plant is
red
Homozygous (2nd allele): No enzyme is produced and so plant is white
Heterozygous: Their single allele for the functional enzyme produces some red and so plant is pink
CR = Red pigment
CW= White pigment
e.g. CRCR + CW CW
CR | CW | |
CR | CRCR | CRCW |
CW | CRCW | CWCW |
Phenotypic Ratio: 1
Pink
e.g. CRCW + CRCW
CR | CR | |
CW | CRCW | CRCW |
CW | CRCW | CRCW |
Phenotypic ratio: 2:1:1
Pink: Red: white