The condition in which neither allele is dominant or recessive is called codominance.

Here's how it works:

* Dominant alleles express their trait even if only one copy is present.

* Recessive alleles only express their trait if two copies are present.

* Codominant alleles both express their traits equally.

Example:

In the case of human blood types, the alleles for A and B are codominant. If someone inherits one A allele and one B allele, they will have blood type AB, expressing both A and B antigens on their red blood cells.

Let me know if you'd like more examples or explanation!