Mutations

A mutation is a permanent change in the DNA sequence of a gene. Mutations in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene. What is a mutation?

How do mutations happen? Like words in a sentence, the DNA sequence of each gene determines the amino acid sequence for the protein it encodes. The DNA sequence is interpreted in groups of three nucleotide bases, called codons. Each codon specifies a single amino acid in a protein. How do mutations happen?

We can think about the DNA sequence of a gene as a sentence made up entirely of three-letter words. In the sequence, each three-letter word is a codon, specifying a single amino acid in a protein. Have a look at this sentence: Thesunwashotbuttheoldmandidnotget hishat. Mutate a sentence

Thesunwashotbuttheoldmandidnotget hishat.   If you were to split this sentence into individual three-letter words, you would probably read it like this: The sun was hot but the old man did not get his hat.

This sentence represents a gene. Each letter corresponds to a nucleotide base, and each word represents a codon. What if you shifted the three-letter "reading frame?" You would end up with: T hes unw ash otb utt heo ldm and idn otg eth ish at. Or Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.

Now, going back to the original sentence: Thesunwashotbuttheoldmandidnotget hishat.   See how you can mutate the reading frame of this sentence by inserting or deleting letters within the sentence.

What types of mutations can occur in DNA sentences? Point mutations are single nucleotide base changes in a gene's DNA sequence. This type of mutation can change the gene's protein product in the following ways: What types of mutations can occur in DNA sentences?

Missense mutations are point mutations that result in a single amino acid change within the protein. Nonsense mutations are point mutations that create a premature "translation stop signal" (or "stop" codon), causing the protein to be shortened. Silent mutations are point mutations that do not cause amino acid changes within the protein.

Insertion mutations and deletion mutations add or remove one or more DNA bases. Insertion and deletion mutations cause frameshift mutations, which change the grouping of nucleotide bases into codons. This results in a shift of "reading frame" during protein translation.

Gene mutation vs. Chromosomal mutation Gene mutation: Changes or shifts in one or more nucleotides. (Point mutations or frameshift mutations) Chromosomal mutation: Changes in the number or structure of chromosomes. Gene mutation vs. Chromosomal mutation

Significance of mutations Most mutations have no effect on gene expression. Some will cause changes in protein production and will disrupt normal biological activities. Some mutations produce genetic variety in a species and be highly beneficial. Significance of mutations