R R' R RR RR' R' RR' R'R'
Let's consider a fish-themed example to illustrate codominance and incomplete dominance. Suppose we have a fish population with two alleles that control the color of their scales: R (red) and B (blue). The possible genotypes and phenotypes are:
| Question # | Correct Answer | Common Mistake to Watch For | | :--- | :--- | :--- | | 1 | 1. Red, 2. White, 3. Pink | Writing "Red and White" for Pink (That’s codominance) | | 2 | 50% Pink, 50% White | Forgetting to list both Genotype AND Phenotype | | 3 | 1:2:1 (Red:Pink:White) | Writing 3:1 (That’s Mendel’s ratio, not incomplete dom.) | | 4 | Red and White stripes | Writing "Pink" | | 5 | 50% Red, 50% Striped | Writing "25% White" (White requires two ( F^W ) alleles) | | 6 | 1 Red : 2 Striped : 1 White | Confusing Striped fish with Blended fish | | 7A | First cross (Green) | Forgetting that "blending" = Incomplete | | 7B | Second cross (Patches) | Forgetting that "both" = Codominant | | 8 | False | Saying "True" because they saw a 1:2:1 ratio | | 9 | 0% | Saying 25% or 50% |
| | ( F^R ) | ( F^W ) | | :--- | :--- | :--- | | ( F^R ) | ( F^R F^R ) (Red) | ( F^R F^W ) (Striped) | | ( F^W ) | ( F^R F^W ) (Striped) | ( F^W F^W ) (White) |
Before diving into the answer key, let’s review the definitions, as these are the most common points of confusion on the worksheet.