Which of the following conditions represent a case of co-dominant genes.

Options

A. a gene expresses itself, suppressing the phenotypic effect of its alleles
B. genes that are similar in phenotypic effect when present separately, but when together interact to produce a different trait
C. alleles, both of which interact to produce a trait, which may or may not resemble either of the parental types
D. alleles, each of which produces an independent effect in a heterozygous condition

Explanation

To determine which of the given conditions represents a case of co-dominant genes, we need to understand the concept of co-dominance in genetics.

### Step-by-Step Solution:

1. **Understand Co-Dominance**: Co-dominance occurs when both alleles in a heterozygous individual contribute to the phenotype independently and distinctly. This means that both traits are expressed simultaneously without blending.

2. **Analyze the Options**: We will evaluate each option provided to see which one aligns with the definition of co-dominance.

- **Option 1**: "A gene expresses itself suppressing the phenotypic effect of its alleles."
- This option suggests that one allele suppresses the effect of the other, which is not characteristic of co-dominance.
- **Conclusion**: Incorrect.

- **Option 2**: "Genes that are similar in phenotypic effect when present separately but together introduce a different trait."
- This implies that the alleles produce a different trait when combined, which does not align with co-dominance where both traits are expressed distinctly.
- **Conclusion**: Incorrect.

- **Option 3**: "Alleles both of which attract to produce a trait which may or may not resemble either of the parent types."
- This option suggests a blending or intermediate trait, which is not a characteristic of co-dominance.
- **Conclusion**: Incorrect.

- **Option 4**: "Alleles each of which produces an independent effect in heterogeneous condition."
- This option accurately describes co-dominance, as both alleles are expressed independently in the phenotype.
- **Conclusion**: Correct.

3. **Final Answer**: Based on the analysis, the correct option that represents a case of co-dominant genes is **Option 4**.