25.4
Gene Mutation
Gene Mutations
Mutation: a permanent genetic change
Gene Mutation: a change in the sequence of
bases within a gene
Ex.: THE CAT ATE THE RAT
Frameshift Mutations: changes the length
of the codon sequence through nucleotide
addition or deletion
• Occur most frequently
• can result in a non-functional protein
Addition: THE ECA TAT ETH ERA T
Deletion: THC ATA ET HER AT
Point Mutations: a change in a single
nucleotide, changing the codon
Substitution: point mutations that occurs
when one base is exchanged for another
Silent Mutation: when the substitution has no
noticeable effect (still codes for the same
amino acid)
Ex.: UAU become UAC
Types of Mutations
Nonsense Mutation: substitution changes
amino acid codon to stop codon
• Ends too early, may be unable to function
• Ex.: UAC changes to UAG (from tyrosine to
stop)
Missense Mutation: substitution changes
amino acids, resulting in wrong sequence
• May or may not affect protein function/shape
• Ex.:: if UAC canges to CAC, histidine
incorporated into protein instead of tyrosine
Rearrangements can also occur – genes can
be moved to different locations
Ex.: ATC GCC  ACT GCC
Tandem Repeats: copies of repeated codons
Ex.: ATC GCC  ATC ATC GCC
Protein Folding and Stability
Sickle Cell Disease
• Codon for glutamic acid (GAA) changed to
valine (GUA)
• Changes hemoglobin’s
structure
▫ Glutamic acid is
polar, valine is
nonpolar
Causes of Mutations
1) Spontaneity – especially with point
mutations
2) Mutagens: substances that cause mutations
(ex. radiation such xrays/UV light and
organic chemicals like pesticides)
▫ Can cause bases to mispair, change
chemical structure of bases, substitute for
nucleotides
▫ Xrays and gamma rays: electrons absorb
energy, becoming free radicals
Body-Cell VS. Sex-Cell Mutation
• Somatic cell mutations aren’t passed to
next generation
▫ Occur in body cells
• Neutral Mutations: doesn’t affect
organism (ie. codes for same a.a., occurred
in exon, etc.)
• Mutations in sex-cells (germ-line cells) are
passed onto offspring
▫ May not affect parent, but could impact
offspring
▫ When mutation results in abnormal
protein in sex cell, organism is impacted
▫ Organism not impacted when abnormal
protein in an isolated body cell