For example, cattle breeders select the largest bull to father the next generation of calves, resulting in larger animals-and more meat on the table. By selecting the most desirable parents, breeders increase the chance that the genes responsible for their valuable traits will be passed on to the next generation. Today, biotechnology makes it possible to enter the genetic world of plants and animals-to gain a greater degree of control over the selection of genes than was possible with traditional breeding. Animal material, for instance, can be transferred into plants. Finding One's Way Within a Cell One of the main challenges for biotechnologists is to find their way around the extremely complex, microscopic world within the cell.
Cells can contain thousands of genes.
The complete set of instructions for making an organism is called its genome. A genome contains the master blueprint for all cell structures and activities for the lifetime of the cell or organism. Found in every nucleus of every cell, an organism's genome consists of tightly coiled threads of DNA and associated protein molecules, organized into structures called chromosomes. DNA molecules consist of two strands that wrap around each other to resemble a twisted ladder. The ladder's sides are connected by rungs of chemicals called bases, which are arranged in pairs.