Mutations in DNA

Mutations

• A mutation is a change in a DNA sequence. • Can happen if – There is a mistake in replication.– Bases change spontaneously due to random

movement of atoms in the DNA molecule. – In contact with chemicals, radiation, or

ultraviolent rays. They make more frequent errors in base pairing.

Types of Mutations

–Point Mutations or Substitutions: bases are mismatched

GAG CTC GAG Valine

Correct DNA Correct mRNA Correct AA

GCG CTC GGG Glycine

A should pair with T, but instead G is mismatched to T

Point mutation mutated mRNA Wrong AA

Mutations

• Example: Sickle Cell Anemia• http://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_06

Insertion: one or more new nucleotide pairs are inserted into a gene.

Correct DNA: ATA CCG TGA TAT GGC ACT

Correct mRNA: UAU GGC ACU

Correct amino acids: Tyrosine Glycine ThreonineExtra inserted base shifts how we read the codons (3 bases), which changes the amino acids

Frameshift mutation ATG ACC GTG Ain DNA: TAC TGG CAC T

Mutated mRNA: UAC UGG CAC U

Wrong amino acids: Tyrosine Tryptophan Histadine

Deletion- One or more nucleotide pairs are deleted.

Mutations

• If a mutation happens in a sex cell (sperm or egg), it may be passed on to future generations.

• Frameshift Mutation: Deletions and insertions of one or two nucleotides can have catastrophic effects on genes because all the codons that follow the deletion or insertion will be altered.

Example

THE DOG SAW THE CATor

THD OGS AWT HEC AT

Overall Types of Mutationsadd to the bottom of note sheet

• Missense : ANY mutation that alters the codon so as to produce an altered amino acid in the protein

• Nonsense : ANY mutation that changes a codon that specified an amino acid to one of the STOP codons

• Silent : ANY mutation that causes no change in the protein and cannot be detected without sequencing the gene

Four Outcomes of Nucleotide Substitutions

1. The protein may be unchanged. 2. The new protein may be equivalent to the

original one. 3. Protein function may be changed by an

altered amino acid sequence. 4. Protein function may be destroyed by a

premature stop codon.

Rate of Mutations in Human Gametes.

• In humans, mutation rates range from about 1 in every 100,000 gametes to 1 in 1,000,000 gametes.

Mutations to control genes can transform one body part into another. Scientists have studied flies carrying Hox mutations that sprout legs on

their foreheads instead of antennae!

Sickle Cell Anemiahttp://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_06

Name Mutationshttp://www.nature.ca/genome/04/0413_e.cfm