The basic unit of classification of living things is species. species is the smallest unit containing members which have the largest number of features in common and usually interbreed among themselves.
Thus, the group of deer describes a specie since they can interbreed freely and are similar in characteristic features.
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.
