Variations among organisms or genetic variation mean that all biological systems, individuals and populations are different and that variation can be identified at a variety of levels.
Genetic variation is caused by variation in the order of bases in the nucleotides in genes and it can occur in both, coding regions and in the non-coding intron region of genes. New technology now allows scientists to directly sequence DNA and examine those variations. As a consequence, the genetic variation can result in phenotypic variation(different observable characteristics).
Variation in the order of nucleotides in the DNA sequence makes a difference in the order of amino acids in proteins coded by that DNA sequence. Differences in amino acid sequence influence the shape, and thus the function of the enzyme or some other proteins.