The Cell Cycle

13.3 Mutations Mutations – heritable changes in genetic information (changes to the DNA sequence) Two types - gene and chromosomal mutations Mutations can be caused by chemical or physical agents (mutagens) Chemical – pesticides, tobacco smoke, environmental pollutants Physical – X-rays and ultraviolet light

13.3 Mutations Gene mutations Point Mutation: mutations that affect a single nucleotide Frameshift mutation: shift the reading frame of the genetic message. Can change the entire protein so it doesn’t work Gene Mutations Explained

13.3 Mutations

13.3 Chromosomal Mutations Chromosomal mutation: mutation that changes the number or structure of chromosomes.

13.3 Chromosomal Mutations Types of chromosomal mutations: Deletion: The loss of all or part of a chromosome Duplication: A segment is repeated Inversion: part of the chromosome is reverse from its usual direction. Translocation: one chromosome breaks off an attaches to another chromosome.

Karyotype of a normal male Nondisjunction Karyotype of a Patau’s male (notice chromosome #13 has three chromosomes instead of two) Karyotype of a normal male

Silent and nonsense mutations Silent: an alteration in a DNA sequence that does not result in an amino acid change because many codons code for the same amino acid. For instance: GAA and GAG both code for amino acid GLU Nonsense mutation: replacement of one base in the DNA code results in a “stop” codon therefore shortening the protein.