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Lecture 26: Mutations & Polymorphisms (Types of mutations (Through…
Lecture 26: Mutations & Polymorphisms
The larger the genome size, the lower the rate of mutation
Types of mutations
Mismatch mutations: error in replication
Through tautomeric shifts, bases can incorrectly pair
T pairs with G not A
A pairs with C not T
G pairs with T not C
Single-stranded DNA backbone break
Missing base
Bulky side group attached to a base
Cross-linked thymine bases
Double-stranded DNA backbone break
Alkylation-induced specific mispairings
DNA polymerase proofreads the genome
Other sources of mutations:
Transposable elements (retrotransposons)
UV radiation
Causes thymine dimers
Cytosine demethylation
Removes entire cytosine from backbone- source of cancer
Ionizing radiation (like X-rays)
Environmental mutagens
Blood types are based on membrane proteins
Different codons can specify the same amino acid (usually just the last base pair that is different)
Other way of classifying mutations
Nonsense (stop codon)
Nonsynonymous
Readthrough (stop codon replaced with amino acid)
Synonymous (doesn't change amino acid)
Most mutations affect noncoding regions
Some amino acids have similar chemical properties-function in similar ways