The answer is genes. Genes is the simplest unit in terms of function and physical unit of heredity. These are made of enormous number of DNA which act as the intructions to make the molecules needed by the organisms. Each organism have two copies of genes, usually one is inherited from the parent. Alleles are forms of same gene with slight differences in the DNA sequence. This can help in the unique physical attribute of the organism. Each genes are made of DNA. Each chromosome contains many genes.
