Define/Explain: Co-dominance.

(N/A) Co-dominance is a phenomenon in which both alleles of a gene pair express themselves equally in the $F_1$ generation. In this case,the $F_1$ generation resembles both parents. $A$ classic example of co-dominance is the $ABO$ blood grouping system in humans,where individuals with $I^A I^B$ genotype express both $A$ and $B$ antigens on the surface of their red blood cells.