Chapter 12.4 Mutations

Kinds of Mutations Mutations are changes in the genetic material. Sometimes when DNA is copied mistakes are made where there is an incorrect base or a base skipped. These are mutations. Mutations that produce a change in a gene are called gene mutations. Mutations that cause changes in whole chromosomes are called chromosomal mutations.

Gene Mutations Point mutations are mutations that occur at a specific point. These include substitutions – where one base is changed into another. As well as insertions and deletions – adding or removing a base. Example: Original DNA TTCGAA Point mutation substitution – TTCCGAA Substitution mutations usually only affect one codon so only a single amino acid.

Frameshift mutations are mutations that shift the reading frame Frameshift mutations are mutations that shift the reading frame. It is an insertion or deletion of a base. Original DNA - TTCGAA Frameshift mutation insertion – TGCGAA Frameshift mutation deletion – TCGAA This mutation will affect all the amino acids following the mutation.

Chromosomal Mutations This is changing the number or structure of chromosomes. This may move the location of certain genes or change the number of copies of some genes. There are 4 types of chromosomal mutations: Deletions – losing all or part of a chromosome Duplications – make extra copies of parts of chromosomes Inversions – reversing the direction of parts of chromosomes Translocations – part of 1 chromosome breaks off and attaches to another

Significance of Mutations Many mutations are neutral – they do not change the gene. Mutations that cause dramatic changes are usually harmful. Mutations cause many genetic disorders like sickle cell anemia, cystic fibrosis, cancer. Mutations can be beneficial in plants polyploidy – complete extra sets of chromosomes can produce larger and stronger plants.