a 1 picogram = 965 million base pairs, haploid nucleus
b DNA content of unreplicated haploid chromosome complement
Source: Data from Arumuganathan and Earle, 1991.
have added genes to potatoes from bacteria, viruses, chickens, and moths. The foreign gene can also be modified by molecular techniques before introduction into the plant (for example, by incorporating DNA base pair substitutions).
However, a key question is whether the fact that genes can be obtained from broader sources for plant biotechnology inherently impacts the safety of the resulting genetically engineered organism (see section 2.2.1 and section 2.4.2). Foreign genes engineered into plants may or may not be homologous to genes already present in the plant or the food supply.
1.3 HISTORY AND IMPACT OF BREEDING METHODS
Selection for desirable traits and hybridization has been used since the advent of human agriculture, but the logic underlying the inheritance of traits was not discovered until the middle 1800s. In the 1860s, Gregor Mendel demonstrated the process of heredity by hybridizing different varieties of pea (Pisum sativum) and examining traits such as flower and seed color, seed and pod shape, flower position, and plant height in sub-