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From a growth culture of the host cells, those containing the DNA 
fragment of particular interest are selected and allowed to multiply. 
The resulting population of identical cells is called a "clone. "* In some 
experiments the DNA will be extracted from the cells for study; in 
others, the properties of the cells themselves will be investigated. 
In the experiments discussed in the Guidelines, the host cells are 
generally single -cell microorganisms such as bacteria, or animal or 
plant cells that were originally obtained from living tissue but are grown 
as single cells under special laboratory conditions. 
The process of producing recombinant DNA molecules and intro- 
ducing them into cells is illustrated in Figure IV- 3. 
Recombinant DNA technology represents a method that is applicable 
to many areas of biological research. Essentially, it represents a new 
tool. 
Indeed, investigations carried out under a variety of NIH Institutes 
and programs, and many non-NIH-supported studies in the United States 
and throughout the world as well, are utilizing this technique, much 
as a new instrument may be applied to studying many different things. 
Diverse areas of biological research to which recombinant DNA 
experiments are already being applied include studies of-- 
• bacterial enzymes and metabolism, 
• the synthesis of hormones (e.g. , insulin), 
• the reproduction of viruses, 
• the organization of chromosomes, and 
• the structure and regulation of genes coding for the synthesis 
of globin (hemoglobin), immunoglobulins, histones, and ovalbumin 
(egg protein). 
Thus, except with the aim of improving the technology, investigations 
of "recombinant DNA" per se will not occur. Rather, recombinant DNA 
technology will be used, where applicable, as an additional tool for 
increasing understanding of normal and abnormal biological processes. 
*The word "clone" means a population of cells derived from a single 
cell. In recombinant DNA experiments, it refers to a population of 
single cells with identical DNA content — thus the term ^'molecular 
cloning. " Molecular cloning is therefore different from the growth of 
whole organisms (e.g., frogs) from single cells, a process which is 
also called "cloning. 1 
