Mutations

Mutation A permanent, heritable change in the DNA of an organism. One or several nucleotides can be added, deleted, or replaced. Most mutations are neutral, many are harmful, some are lethal, and a few are beneficial.

Mutations Can Alter Phenotypes Mutations in genes can result in changes to the phenotype by altering the shape (and therefore the function) of the resulting protein.

What causes mutations? Mutations often happen when mistakes occur during replication. Also caused by mutagens like UV light, radiation, and certain chemical toxins.

How often do mutations happen? Mutations are rare events. The average rate of mutations is one in a million replications.

Are mutations always harmful? Most mutations produce no observable effect – they are “neutral.” Of those that have significant effect, most are harmful or lethal. Some mutations are beneficial. It all depends on the environment in which the mutation occurs. Examples: General & Humans

Types of mutations Point mutation: a different nucleotide replaces the original Missense: results in a single amino acid change (altered protein) Nonsense: results in a premature stop codon (shortened protein) Silent: results in the same amino acid (unaltered protein)

Missense Mutation

Nonsense Mutation

Silent Mutation

Types of mutations Frameshift mutation: a deletion or insertion that alters the "reading frame" causing the codons that follow it to be changed

Normal Protein → Normal Function A A U|U A C|U G C|U C U|G G A|G A G|U G U|G A A|U U U|G U G Asn Tyr Cys Ser Gly Glu Cys Glu Phe Val Normal Protein → Normal Function A A U|U A C|U G C|U C U|G G A|G A G|U G A|A U U|U G U|G U U A A U|U A C|U G C|U C U|G G A|G A G|U G A|A U U|U G U|G U U U|G A A|U U U|G U G U U Asn Tyr Cys Ser Gly Glu Shorter Protein → Loss of Function

(A) Dogs have two copies of the wild-type allele (+/+). (B) Dogs are heterozygous with one wild-type allele and one mutant cys → stop allele (mh/+). (C) Dogs are homozygous for the mutant allele with two copies of the cys → stop mutation (mh/mh).

Are you a mutant? A. Yes B. No Scientists estimate about 1-6 point non-silent mutations in coding DNA per individual. The total number of point mutations per individual is much higher, but almost all of these are either silent or are in non-coding DNA. These are the mutations you inherited from your parents. However, since DNA replication takes place in your body so many times during your lifetime, many of your cells likely contain mutations. A. Yes B. No

What is a Mutation?

Mutate a Sentence! We can think about DNA gene sequence as a sentence made up entirely of three-letter words. In the DNA sequence, each three-letter word is a "codon," specifying a single amino acid in a protein.

Mutate a Sentence! Have a look at this "sentence": thesunwashotbuttheoldmandidnotgethishat If we were to split this sentence into individual three-letter words, we would read it like this: The sun was hot but the old man did not get his hat

Mutate a Sentence! The sentence represents a gene. Each letter corresponds to a nucleotide, and each word represents a codon. Only one of the three possible "reading frames" translates into an understandable sentence. In the same way, only one three-letter "reading frame" within a gene codes for the correct protein.

Mutate a Sentence! What if you shifted the three-letter "reading frame?“ In the space below, show how you can change the "reading frame" of the above sentence by inserting or deleting letters within the sentence. The result should be a "nonsense" sentence.

Mutate a Sentence! X The sun was hot but the old man did not get his hat hes unw ash otb utt heo ldm and idn otg eth ish at

Mutate a Sentence! Now make a mutation that maintains or changes the meaning of the sentence without creating such nonsense. The sun was hot but the old man did not get his hat The sun was hot but the old man did get his hat The sun was hot but the old man did not eat his hat The sun was not hot but the old man did get his hat