 Often different genes can interact in a way that influences the same trait . In the Blue @-@ eyed Mary ( <unk> verna ) , for example , there exists a gene with alleles that determine the color of flowers : blue or magenta . Another gene , however , controls whether the flowers have color at all or are white . When a plant has two copies of this white allele , its flowers are white — regardless of whether the first gene has blue or magenta alleles . This interaction between genes is called <unk> , with the second gene <unk> to the first . 
