Mutations Section 12-4

Objectives for this section  Contrast gene mutations and chromosomal mutations

Kinds of Mutations  Mutations are changes in the genetic material  Gene mutations—mutations that produce changes in a single gene

Kinds of Mutations  Point mutations—gene mutations involving one or a few nucleotides Include:  Substitutions—one base is changed to another Usually affect no more than a single amino acid

Kinds of Mutations  Insertions and deletions—a base is inserted or deleted from the DNA sequence Can have a very dramatic effect—remember that codons are read in groups of 3, so adding or deleting a base causes the rest of the bases to be read incorrectly

Kinds of Mutations  This is called a frameshift mutation, because it shifts the reading frame of the genetic message  Frameshift mutations can alter a protein so much that it us unable to perform its normal functions

Frameshift Mutations

Kinds of Mutations  Chromosomal mutations—mutations that produce change in whole chromosomes Involve changes in the number or structure of chromosomes May change the locations of genes of chromosomes May even change the number of copies of some genes

Kinds of Mutations  Four types of chromosomal mutations: Deletions—loss of all or part of a chromosome Duplications—produce extra copies of parts of a chromosome Inversions—reverse the direction of parts of chromosomes Translocations—when part of one chromosome breaks off and attaches to another

 Deletion (A)  Inversion (B)  Translocation (C)  Duplication (D)

Significance of Mutations  Many, if not most, mutations are neutral. This means that they have little or no effect on the expression of genes or the function of the proteins for which they code.  Mutations that cause dramatic changes in protein structure or gene activity are often harmful, producing defective proteins that disrupt normal biological activities.

Significance of Mutations  Mutations are not all bad—they are the source of genetic variation in a species—some of this variation may be highly beneficial.  Some breeders take advantage of mutations— polyploidy Plants that are polyploidy (meaning that the organism has an extra set of chromosomes) are often much larger and stronger than diploid plants.