WordNet sense 1 (an allele that produces the same phenotype whether its paired allele is identical or different):

dominant allele

WordNet sense 2 (greatest in status or authority or power):

sovereign, supreme

WordNet sense 3 (having superior power and influence):

overriding, paramount, predominant, predominate, preponderant, preponderating

WordNet sense 4 (responsible for making and enforcing rules and laws):

governing

WordNet sense 5 (able to control or determine policy):

controlling

WordNet sense 6 (most powerful or important or influential):

ascendant