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Mutations Types of Mutations • Gene mutation – a mutation that only affects one gene • Types of mutations can be determined by Type Description Example • Step 1 | Write the wild-type allele …TAGCCAGATA… above the mutated allele so that the Insertion A new nucleotide is added …TAGCGCAGATA… bases line up. …TAGCCAGATA… • Step 2 | Starting on the left, look Deletion A nucleotide is removed …TAGCAGATA… along both strands and underline Substitution A nucleotide is replaced …TAGCCAGATA… the first base that is different in the (point mutation) with a different nucleotide …TAGCCAGTTA… mutated allele. • Step 3 | Based on the difference between the two strands, identify the mutation that occurred. • Step 4 | If possible, use the overall lengths of the two strands to check your answer. • Chromosomal mutation – a mutation that affects multiple genes • Deletion • Amplification • Inversion • Insertion • Translocation • Some mutations happen during meiosis • Non-disjunction – an event in which the homologous chromosomes do not separate and instead both go to the same daughter cell Biology 6.3 – Mutations Mutations Effects of Mutations • Gene mutations can have different effects • Chromosomal mutations affect multiple genes • Have large impact on organism • Non-disjunction creates one gamete with extra copy and one with no information • If either fuses with normal gamete, individual formed has abnormal number of chromosomes • Ex) Down syndrome – a human genetic disorder caused by having an extra chromosome #21 • Physical and mental retardation • Overexpression – the creation of more protein than normal from a gene • If chromosome segment is deleted or inversed, organism might not be able to express any of the genes • Beneficial mutations – a mutation that increases an organism’s fitness • Ex) Fur color may allow organism to better blend into the environment, avoiding predators • Harmful mutation – a mutation that decreases an organism’s fitness • Ex) May make protein used to carry oxygen less efficient • Neutral mutation – a mutation that does not affect an organism’s fitness • All silent mutations are neutral mutations Biology 6.3 – Mutations Mutations Causes of Mutations • Mistakes that happen during DNA replication • Mutagen – an environmental agent that can damage DNA • Ultraviolet radiation and chemical toxins • Spontaneous damage by free radicals – reactive forms of molecules made by metabolism • Cause damage directly to nitrogenous bases of DNA • Antioxidants thought to neutralize free radicals • Checkpoint procedures during cell cycle prevent cell division if mistakes are found in DNA • Cells that do not pass checkpoint are marked for destruction • Mutations can accumulate if checkpoint system breaks down • If mutation removes checkpoint, cells with damaged DNA can replicate • Cells can repair own damage • UV radiation can be repaired when the damaged section of the strand is removed • Enzymes identify abnormal nitrogenous bases and chemically cut them out • Sometimes cannot repair damage • Ionizing radiation (from X-ray machines) causes physical breaks in one or both strands of DNA • Pieces of chromosome are lost or become attached to other chromosomes • Very dangerous and protection should be used when exposed to it • Babies and young children should take extra precautions to prevent mutations • Rapidly dividing cells are more susceptible to radiation, UV light, and free radicals • Extra precautions should be taken during pregnancy • Damage from mutagens accumulates as we age Biology 6.3 – Mutations