What is mutation?
• Mutation is a change in the sequence of bases in DNA or RNA
• They are heritable changes in the genetic information
• Mutations drive evolution
Mutations in non-coding DNA;
• Mostly harmless
• SNPs (single nucleotide polymorphisms); it is called for a mutation when more than 1%
of population has the mutation
1
, o If it happens in the non-coding region; it is harmless
o If it happens in the coding region; you could have a change in the function of the
gene but it will still be functioning because it is polymorphism. (You can survive with
this mutation)
Classification of mutations;
1. Gene mutations (DNA mutations); arise during replication or recombination
o Base substitutions (point mutations) (synonymous)
o Deletion (nonsynonymous)
o Insertion (nonsynonymous)
2. Chromosomal mutations
• Synonymous mutations: do not alter amino acid sequence (and are sometimes silent
mutations)
• Nonsynonymous mutations: alters the amino acid sequence of a protein
Base substitutions (point mutations);
• Transition; purine is substituted with another purine/pyrimidine is substituted with
another pyrimidine
• Transversion; purine is substituted with another pyrimidine/pyrimidine is substituted
with another purine
Occurrence types of point mutations;
• Silent; change in 3rd nucleotide such that due to wobble pairing same amino acid is
specified (no effect to the protein)
• Missense; one base change causes an amino acid to change
o Conservative missense; the change is very small
o Non-conservative missense; the change is very big
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, • Nonsense; one base change causes an amino acid to change to a stop codon
• Neutral; changes are neither beneficial nor detrimental
Deletion and insertion
• They result in frameshift
• Insertion is adding one or more nucleotides to the sequence
• Deletion is removing one or more nucleotides to the sequence
• Insertion or deletion of multiples of 3 are in-frame since they do not alter the reading
frame of the genetic code
Types of chromosomal mutations
• Variation in chromosome structure
• Variation in number of chromosomes
Types of variations in chromosome structure
• Deletion; a portion of the chromosome breaks and get lost
• Duplication; a part of the chromosome is copied and additional genetic material is
present
• Inversion; to take a part of the chromosome turn it around and put it back in
o Pericentric inversion; includes centromere
3
, o Paracentric inversion; does not include centromere
• Translocation; a piece of one chromosome breaks off and attaches to another
chromosome
• Insertion; a portion of the chromosome is inserted to another chromosome
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