 The set of alleles for a given organism is called its genotype , while the observable traits of the organism are called its phenotype . When organisms are heterozygous at a gene , often one allele is called dominant as its qualities dominate the phenotype of the organism , while the other allele is called recessive as its qualities recede and are not observed . Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype , or <unk> by expressing both alleles at once . 
