Why do children resemble their parents and yet are still different?
Why can we recognize the different species and varieties of animals and plants?

The characteristics of form, function and behavior of organisms are passed from generation to generation through genetic information. Information on the size, color, number of flowers, fruits, operation of the senses and behavior of the organism is found in the genetic code. The set of transmissible characters is known as genotype and its expression (anatomy, physiology and behavior) is known as phenotype.

Within the nucleus of cells of living beings (except for those of the Archaea and Bacteria) are organelles shaped like sticks, known as chromosomes (from the Greek chrome, color and body soma). The name comes from their staining properties. Each species has a characteristic number of chromosomes. Some species have few chromosomes, while others have many; maize has 10 pairs, some butterflies have more than 200 pairs and humans have 23 pairs.

Chromosomes are composed of long chains of molecules of deoxyribonucleic acid (or DNA for short). These chains are divided into functional segments containing particular information, known as genes. The gene is the unit of storage and transmission of information regarding heredity of the species.