Mutations Notes
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Mutations and Other Mistakes Mutations Sometimes cells make mistakes when replicating their own DNA, inserting an incorrect base or even skipping a base as the new strand is put together What is a Mutation? Mutations = changes/mistakes in the sequence of nitrogen bases made in the DNA Can be caused by mutagens = any agent that causes a mutation Examples: X-rays, UV light, nuclear radiation, asbestos, cigarette smoke , etc Two types: Gene mutations- when a single gene is affected Chromosomal mutations- changes in the number or structure of a chromosome. When do Mutations Occur? Mutations can occur during: preparation for cell division -mitosis protein synthesis meiosis (production of gametes = sex cells) If a mutation occurs in a sperm or egg cell, that mutation is passed onto offspring If a mutation occurs in a body cell, that mutation affects only the organism and is not passed onto offspring Types of Mutations Gene Mutations Chromosomal Mutations Types of Mutations Gene Mutations occur at a single point in the DNA Point sequence . Only one (or a few) bases are affected. Chromosomal Mutations Types of Mutations Gene Mutations Point Substitutions When 1 DNA base is changed to another Chromosomal Mutations Substitution when one based is changed to another, usually causes a change in one amino acid, or a stop in the protein Types of Mutations Gene Mutations Point Substitutions Silent a base is changed, but the amino acid that it codes for is not changed. Chromosomal Mutations Silent Mutations a base is changed, but the amino acid that it codes for is not changed. Example: DNA code mRNA Amino Acid CAT GUA Valine CAG GUC Valine Types of Mutations Gene Mutations Point Substitutions Causes a “shift” and changes the way the DNA sequence is read Frameshift Silent Chromosomal Mutations Types of Mutations Gene Mutations Point Substitutions Chromosomal Mutations Frameshift Silent Insertion A base is added to the DNA sequence Types of Mutations Gene Mutations Point Substitutions Chromosomal Mutations Frameshift Silent Insertion Deletion A base is removed from the DNA sequence Frameshift Mutations Insertion or deletions cause the amino acids coded to be different because of missing or added nucleotides. Insertions and Deletions Types of Mutations Gene Mutations Point Chromosomal Mutations Frameshift Deletion Loss of all or part of chromosome Substitutions Silent Insertion Deletion Deletions These involve the loss of all or part of a chromosome Ex: ABCDEF ACDEF Turner syndrome when one of the two X chromosomes in females is either missing or incomplete. The most common symptoms are short stature and infertility. Types of Mutations Gene Mutations Point Chromosomal Mutations Frameshift Deletion Duplication Substitutions Extra copies of some of a chromosome made Silent Insertion Deletion Duplications These occur when extra copies of some of a chromosome made Ex: ABCDEFABCDDEF Triple X Syndrome extra X chromosome in each of a female’s cells. Associated with the increased risk of learning disabilities and delayed development of speech and language skills. Down’s Syndrome caused by the presence of all or part of a third copy of chromosome 21 Types of Mutations Gene Mutations Point Chromosomal Mutations Frameshift Deletion Duplication Substitutions Silent Insertion Deletion Inversions Reverse the direction of some of the chromosome Inversions These reverse the direction of parts of the chromosome Ex: ABCDEFEFCDBA Recombinant 8 syndrome A rearrangement of chromosome 8 causes recombinant 8 syndrome, a condition that involves heart and urinary tract abnormalities, moderate to severe intellectual disability, and a distinctive facial appearance. Types of Mutations Gene Mutations Point Chromosomal Mutations Frameshift Deletion Inversions Duplication Substitutions Silent Translocations Insertion Deletion part of one chromosome breaks off and attaches to another Translocations These occur when part of one chromosome breaks off and attaches to another Ex. ABCDEFGHIJKL ABCJKLGHIDEF Acute Promyelocytic Leukemia rearrangement (translocation) of genetic material between chromosomes 15 and 17. blood cells are stuck at the mitosis stage, and they multiply abnormally = cancer This mutation is acquired during a person's lifetime and is present only in certain cells. It is not inherited Are ALL Mutations Bad? No… Depending on the type of mutation and its location, the protein may not be altered. In some cases it can be changed so much that it disrupts the entire sequence and the protein is not made. Mutations can be: Harmful Helpful Neutral Are ALL Mutations Bad? Mutations are significant to living things because they cause genetic variations, which lead to evolution. Harmful Mutations Cause changes in protein shape or gene activity. Biological activities are affected by these. Examples: Cancers Sickle cell anemia Caused by a point mutation that changes the shape of a hemoglobin Helpful Mutations Makes genes with function that are useful to organisms in different environments, Examples: African mosquitoes are resistant to the chemicals that once killed them. Stronger bones in humans Increased resistance to HIV Polyploidy (extra set of chromosomes) in plants makes them bigger and stronger. Sickle Cell Anemia Carriers are protected against malaria.
