The gene that does not express itself and is concealed by the presence of another gene for the same trait is called a recessive gene.

Here's a simple explanation:

* Alleles: Genes come in different forms called alleles. For example, a gene for eye color might have an allele for brown eyes and an allele for blue eyes.

* Dominant and Recessive: Some alleles are dominant, meaning they will always express their trait if present. Others are recessive, meaning they will only express their trait if two copies of the recessive allele are present.

* Example: Let's say brown eyes are dominant (B) and blue eyes are recessive (b). If someone has one brown eye allele (B) and one blue eye allele (b), they will have brown eyes because the brown eye allele is dominant. They still carry the blue eye allele, but it is masked by the brown eye allele.

So, the recessive gene is the one that is "concealed" or not expressed in the presence of the dominant gene.