Some diseases, such as cystic fibrosis, are transmitted by recessive genes. Mutation is the term used for a spontaneous change in a chromosome or gene. Normally chromosomes duplicate themselves exactly during cell division. Occasionally, however, the new cells contain an altered gene or chromosome. If the mutation occurs in an ovum or sperm involved in reproduction, the new trait will be expressed in the offspring.
Many mutations are so minor that they have no visible effect.
A mutation that is very harmful will usually result in the death of the fetus and spontaneous abortion. Occasionally a mutation is beneficial. Favorable mutations gradually tend to spread through a population. The accumulation of mutations over millions of years has contributed to evolution. All rights reserved.