There are approximately 100,000 genes in a human cell, only a small number of which have been identified and roughly located on the various chromosomes. DNA carries chemically coded information from generation to generation, providing instructions for growth, development, and functioning. Through sexual reproduction, new combinations of chromosomes result. One member of each pair of chromosomes is inherited from each parent. This sexual genetic recombination leads to variability within the species.
Mutations are simply chemical changes to the DNA molecule.
Mutations produce much of the variability on which natural selection operates. Variability is the raw material for natural selection. Specialized features of organisms which allow them to perform useful functions are called adaptations . Similar body plans suggest common origins. Analogy - body parts with similar function , without regard to origin.