IV. Source of Gene Variations: When cells divide each DNA molecule in the cell makes exact copies of itself. But sometimes the cell makes a mistake; bases may pair up incorrectly. The codon are changed the altered gene is passed on to the new cell. A- Mutation is any permanent change in the DNA of a cell. 1. Mutation increases with the exposure of DNA to some chemicals ands radiation that damage the DNA molecule. B. Chromosome Mutation: When a piece of chromosome breaks and are rearranged or lost. During meiosis chromosomes mutation may occur when chromosomes do not separate evenly. 1. Muscular Dystrophy= Weak muscles. 2. Down Syndrome or Trisomy 21= is caused as a result of a sex cell having too many 21st chromosomes. The fertilized egg, contains three 21st chromosomes instead of two. 3. Importance of Mutations= are a source of new traits or new forms of traits.