Incomplete Dominance Is When Neither Allele Is Completely Dominant
- Incomplete dominance and codominance are two distinct patterns that differ at the phenotypic level.
- In addition to the codominance seen in the ABO blood group system, there are other inheritance patterns where neither allele is completely dominant.
Incomplete Dominance: Heterozygotes Display Intermediate Traits
- In incomplete dominance, neither allele is entirely dominant.
- The heterozygous phenotype represents a blend or intermediate of the two parental traits.
Pink Flowers in Mirabilis jalapa
- CR is the allele for red flowers, and CW is the allele for white flowers.
- Heterozygotes (CRCW) produce pink flowers because neither allele completely dominates.
- Predicting Flower Color
- If two pink-flowered plants (CRCW) are crossed:
- The offspring ratio is 1 red (CRCR), 2 pink (CRCW), and 1 white (CWCW).
- This demonstrates how incomplete dominance leads to a unique intermediate phenotype.
- If two pink-flowered plants (CRCW) are crossed:
| Gametes | $C^R$ | $C^W$ |
|---|---|---|
| $C^R$ | $C^RC^R$ (Red) | $C^RC^W$ (Pink) |
| $C^W$ | $C^RC^W$ (Pink) | $C^WC^W$ (White) |
When solving genetic problems, always define the alleles clearly. For example, use $C^R$ for red and $C^W$ for white to avoid confusion.
