Recessive gene

A recessive gene was a type of gene that would not manifest unless two copies were present. For example, in Human-Skagaran hybrids the Skararan cranial genes were recessive, meaning that in an hybrid with only 1/4th Skagaran ancestry would look Human. 

Within the Borg Collective, acces to Unimatrix Zero was controled by a recessive genetic mutation.