what is an allele is masked
In complete dominance, the effect of one allele in a heterozygous genotype completely masks the effect of the other. The allele that masks the other is said to be dominant to the latter, and the allele that is masked is said to be recessive to the former. Complete dominance therefore means that the phenotype of the heterozygote is indistinguishable from that of the dominant homozygote.