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