Mutations

Mutations

MUTATIONS

Cells have evolved mechanisms to avoid errors during DNA replication. Strands are “proofread” to ensure accuracy and correct any mistakes.

Still, changes in the genetic message (nucleotide sequence of DNA) can occur. Mutations can arise spontaneously or as a result of exposure to mutagens.

Types of Mutations2 Categories : point mutations and chromosomal

POINT MUTATIONS – mutations at a specific base pair. Include:

i) Silent Mutation

- has no effect due to occurring in introns of DNA or

redundant nature of genetic code (e.g.

GAA and GAG both code for glutamic acid)

DNA: CCCATTCTT if CCCATTCTC

mRNA: GGGUAAGAA GGGUAAGAG

ii) Missense Mutation

- alters codon causing it to code for a different

amino acid (e.g. cause of sickle cell anemia)

iii) Nonsense Mutation

- alters codon changing it to a STOP codon and

only part of the protein is translated

- lead to non-functional proteins

iv) Base-pair Insertion/Deletions

- when one or more nucleotide pairs are either

inserted or deleted from a gene

- have a greater effect on proteins than substitutions

- can cause frameshift mutations: occurs when

number of nucleotides inserted/deleted is not 3 or a

multiple of 3

- causes nucleotides to be improperly grouped into

codons producing non-functional proteins (unless at

end of gene)

HEY MAN HOW ARE YOU BRO

Compare to:

HEY MAN HWA REY OUB RO_

HEY MAN HOQ WAR EYO UBR O__

Chromosomal Mutations: - involve large segments of DNA

Duplication

Translocation

Inversion

A B C D E F G

A B E D C F G

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