Genes can be affected and changed by a number of circumstances. Some changes may be beneficial. Other may be harmful. In either case, the effects will be transmitted to one's offspring.
a. A gene may be lost, for example, by a gamete. The resulting off-spring may then not have a certain trait. For example, some individuals are unable to produce a specific enzyme because they do not have the appropriate gene. A metabolic process using that enzyme may be impossible for that individual.
b. Some individuals may have an excessive number of genes. Examples are individuals with an extra X or Y chromosome. This can substantially affect both anatomy and personality.
c. Genetic charts and genetic counseling are sometimes used to advise prospective parents of genetic problems they may expect with their offspring.
d. Technical advances in the biological sciences have made genetic engineering possible. Thus, we see the rise of an industry devoted to altering the genetic makeup of microorganisms for the purpose of producing certain chemicals. The chief value of many of these chemicals will be to correct deficiencies in humans, such as insulin for diabetes. (In cloning, individual cells are cultured to produce numerous organisms, all with the same genotype.)
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