A gene in one strand has the same function as that opposite it in the counterpart strand. We then say that the organism is homozygous with respect to that gene. They may also be different, in which case one of the pair of sequences determines the traits, and the effect of the other is eclipsed. When this happens, the trait of the homozygous state with regards to the dominant allele and this heterozygous state are similar. The alleles may also be equally dominant and the compromise trait is different from that of the homozygous state.
Genes are responsible for the presence of specific enzymes in the cell.
These enzymes influence the complex chemical reactions that are constantly taking place in the cell. Specific traits are, therefore, the outcomes of the interactions among many molecules. The individual steps of the interactions are directed by specific enzymes. In genetic engineering, we introduce specific genes into the cell. An introduced gene may get inside an organelle or inside the nucleus.