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Download Mutations - Biology R: 4(A,C)
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Section 12-4 • Determining the Sequence of a Gene • DNA contains the code of instructions for cells. Sometimes, an error occurs when the code is copied. Such errors are called mutations. • Mutations may result in disorders, diseases, changes in appearance, or they may have no effect at all. Changes in the DNA sequence that affect genetic information Mistakes occur every now and then There are many different types of mistakes: › Inserting the wrong base › Deleting a base › Skipping a base › Etc… Gene mutations result from changes in a single gene Chromosomal mutations involve changes in whole chromosomes Point mutations: mutations that affect one nucleotide occurring at a single point in the DNA sequence › Substituting one nucleotide for another generally change one of the amino acids in a protein In sickle celled anemia a different protein is made In cystic fibrosis a stop codon is made For example: DNA: mRNA: amino acids: TAC-GCA-TGG-AAT AUG-CGU-ACC-UUA Met – Arg – Thr – Leu The 2nd “C” in the DNA is substituted by a “T” DNA: TAC-GTA-TGG-AAT mRNA: AUG-CAU-ACC-UUA amino acids: Met – His – Thr – Leu Frame-shift mutations: mutations that add or remove a nucleotide, shifting the nucleotides (“reading frame”) to make different codons › Adding/removing one nucleotide affects every amino acid following the insertion or deletion severely altering the performance of the protein › For example: THE FAT CAT ATE THE RAT › Deletion of H:TEF ATC ATA TET HER AT Nucleotides are added, so different proteins are made, decreasing strength of muscles For example: DNA: mRNA: amino acids: TAC-GCA-TGG-AAT AUG-CGU-ACC-UUA Met – Arg – Thr – Leu A “T” is added between the 1st A & C DNA: TAT-CGC-ATG-GAA-T mRNA: AUA-GCG-UAC-CUU-A amino acids: Ile– Ala – Tyr – Leu There are four chromosomal mutations: › Deletion: loss of all or part of a chromosome › Duplication: segment of a chromosome is repeated › Inversion: orient part of chromosome in reverse direction › Translocation: part of one chromosome breaks off and attaches to another, nonhomologous, chromosome. Deletion Duplication Inversion Translocation