Mutations

Nitrogen Bases --> Genes --> DNA --> Chromosomes

A section of DNA that directs the making of a specific protein is called a gene. Genes control the traits inherited by an organism. If a change occurs in the sequence of nitrogen bases, the trait may be changed. Any permanent change in the sequence of nucleotides is called a mutation. Some mutations, like flower color in plants, are not harmful, but some mutations can cause disease. For example, sickle cell anemia and cystic fibrosis are diseases caused by mutations. Although many mutations are harmful, they also add genetic diversity to a species. Also, if a mutation causes a change that is beneficial, the individuals with this mutation will have an advantage over organisms without the mutation.

Gene mutations produce a change in a single gene. If a different nucleotide replaces one that was originally present, it is called a substitution mutation. If a base is added, it is called an insertion mutation. If a base is deleted, it is called a deletion mutation.

Chromosomal mutations occur at the chromosomal level. Chromosomal mutations change the number or structure of a chromosome. For example, a piece of chromosome may break off. Chromosomal mutations are more dangerous than gene mutations because of the amount of DNA that is moves, inverted, or deleted.

Mutations are usually random events. Some mutations are caused by mutagens, substances in the environment like ultraviolet light, X rays, radioactive substances, and pollutants. Only changes in gametes (eggs and sperm) are passed on to offspring.

Other mutations occur when a cell copies its DNA in preparation for cell division.