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Transcript
Ch 12-4 Genetic Mutations What is a Mutation? • Changes in the genetic code of DNA Original DNA: ATAGGCCTAGCAGTCG Mutated DNA: ATAGGGCTAGCAGTCG OR Mutated DNA: ATAGGCCTAGCAAGTCG OR Mutated DNA: ATAGGCCTAGAGTCG Mutations can occur in two different types of cells: • Somatic (body) cells – Ex. Skin, heart, liver, lung, blood, muscle • Gamete (sex/reproductive) cells – Ex. Sperm, Egg Mutations in somatic cells • Usually result in killing that body cell only. • Usually do not affect the individual. – Exception: If the mutation occurs in the DNA that controls the cell cycle (division), it can result in cancer. • Can NOT be passed on to the next generation Mutations in Gamete(sex) cells • Means that every cell of the developing fetus/baby will have that mutation. • Usually do not affect the individual with individual with the genetic disorder. • Can be passed on to the next generation There are two types of mutations that can occur. • Gene mutations – Mutations that produce changes in a single gene • Chromosomal mutations – Mutations that produce changes in parts of or whole chromosomes. Type of Single Gene Mutations POINT Two Types of Single Gene Mutations • Point • Frameshift 1. Point Mutation-a single point in the DNA sequence is affected. • Can be a substitution in which one base is changed into another. 1. Point Mutation-a single point in the DNA sequence is affected. • Can be a substitution in which one base is changed into another base during replication. • Example: • Original Sequence DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acid: Met - Arg - Thr - Leu (In this DNA sequence notice the 5th base in the DNA sequence has been changed) Mutated Sequence DNA: TAC GTA TGG AAT mRNA: AUG CAU ACC UUA Amino Acid: Met - His - Thr - Leu Point mutations usually affect no more than a single amino acid. • The protein may be slightly affected or not affected at all. • Ex using a sentence. – THE FAT CAT ATE THE RAT – THE FAT CAT ATE THE HAT Types of Gene Mutations – Frame Shift 2. Frame Shift Mutation • A single gene or nitrogen base is deleted or inserted from the mRNA sequence causing a shift in the “reading frame” of the genetic code. • If a nucleotide is inserted or deleted, the bases are still read in groups of three, so every codon after is changed. • Example: • DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acid: Met - Arg - Thr - Leu *(Notice in this DNA sequence a T has been added to the sequence after the second base) DNA: TAT CGC ATG GAA T mRNA: AUA GCG UAC CUU A Amino Acid: Iso - Ala - Tyr - Leu • The affect of frame shift mutations is usually more dramatic than point mutations. • Frameshift mutations may change every amino acid that follows the point of the mutation. • Frameshift mutations can alter a protein so much that it is unable to perform its normal functions. Example using a sentence • THE FAT CAT ATE THE RAT TEF ATC ATA TET HER AT Chromosomal Mutations: • Involves changes in the number or structure of chromosomes • Can change the locations of genes on chromosomes, and the number of copies of some genes Chromosomal Mutations 5 types of Chromosomal Mutations: 1.Deletion-Loss of all or part of a chromosome. 2.Duplication- extra copies of parts of the chromosome are made. 3.Inversion- reverses the directions of parts of a chromosome. 4.Translocation- Part of a chromosome breaks off and attaches to another chromosome. 5.Non-disjunction- when chromosomes fail to separate during meiosis. Non-disjunction • Results in abnormal numbers of chromosomes. Typically you have 2 of each. – Trisomy (3) means a person has an extra copy of a chromosome. – Monosomy (1) means a person is missing a copy of a chromosome. What causes mutations? • Usually during DNA replication. • Sometimes from Environmental Factors – UV radiation – Chemicals (lead, asbestos) – Pollution – Tobacco smoke – Viruses