National Geographic : 1985 Apr
classic graphic on how to cope. Here is a man up to his chin in monsoon floodwaters, and yet obvi ously delighted with his good fortune in retriev ing his old sewing machine. Edson W. Trumbull West Newton, Massachusetts Genetic Engineering Far better than any current textbook or scientific periodical, your December 1984 article on genet ic engineering explains in clear, concise steps the response of tissue cells to antigens and techniques to change the genetic blueprints. The artwork ac companying this article is equally imaginative and exciting. In fact it has upgraded my knowl edge of this topic immeasurably. John M. Keshishian, M.D. Washington, D. C. In your article about genetic engineering, you in cluded a picture of two genetically identical twin calves. If they are identical, then why are the col or patterns on their heads and legs different? James Zumbro Charleston, South Carolina The hairpatternfortwin calves is geneticallycar ried but not the instructionfor each individual hair; therefore, slight variationswill exist.