Phenotypic ratio in codominance

Options

A. `1 : 2 : 1`
B. `3 : 1`
C. `2 : 1`
D. `2 : 1 : 3`

Answer

To determine the phenotypic ratio in codominance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Codominance**: In codominance, both alleles in a heterozygous organism express themselves fully and simultaneously. This means that neither allele is dominant or recessive.

**Hint**: Remember that in codominance, both traits are visible in the phenotype.

2. **Identify the Alleles**: Let's consider two alleles, A and B. When an organism has one A allele and one B allele (genotype AB), it will express traits from both alleles.

**Hint**: Think of examples where both traits can be seen, like AB blood type in humans.

3. **Crossing the Alleles**: If we cross a pure A phenotype (AA) with a pure B phenotype (BB), the F1 generation will all be heterozygous (AB).

**Hint**: Visualize the Punnett square for this cross to see the offspring.

4. **Self-Pollination of F1 Generation**: When we self-pollinate the F1 generation (AB x AB), we can determine the genotypes of the F2 generation. The possible genotypes will be:
- AA (homozygous for A)
- AB (heterozygous)
- BB (homozygous for B)

5. **Determine Genotypic Ratio**: The genotypic ratio from this self-pollination will be 1 AA : 2 AB : 1 BB.

**Hint**: Count the combinations from the Punnett square to find the ratio.

6. **Determine Phenotypic Ratio**: Since both A and B alleles are expressed in the AB genotype, the phenotypic ratio will match the genotypic ratio. Therefore, the phenotypic ratio is also 1 (A phenotype) : 2 (AB phenotype) : 1 (B phenotype).

**Hint**: Remember that in codominance, the phenotypes reflect the genotypes directly.

### Conclusion:
The phenotypic ratio in codominance is 1:2:1, which is the same as the genotypic ratio.

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