Answer the following question given this paragraph: 

A characteristic may be controlled by one gene with two alleles, but the two alleles may have a different relationship than the simple dominant-recessive relationship that you have read about so far. For example, the two alleles may have a codominant or incompletely dominant relationship. The former is illustrated by the flower in Figure below , and the latter in Figure below .


Q: How many alleles control a characteristic?


A:
2