Genes is found in the DNA. It decides a specific characteristic. Genes can transform and take two or more option structures and these structures are called Alleles. Presently allele happens in an altered spot in a chromosome and in people we have two arrangements of chromosomes.
There are 46 chromosomes in the human. 23 from the dad, 23 from the mother = 46 chromosomes.
This feature of DNA is termed complimentary base pairing, in that the base that compliments a certain base, say A, is always paired with base T, and likewise every T has its pair partner always as A. The same holds true with C with G, and vice versa.
The answer should be proteins. Because the protein is consists of different kinds of amino acids(usually 20 in total). And our cell can not produce essential amino acids itself.