What happens when we change DNA? MUTATIONS

 What do you think a mutation is?  What happens to you during a mutation? MUTATIONS

 Mutations are ANY change in an organism’s DNA.  Mutations usually happen during if a mistake is made during replication (S phase). MUTATIONS

 As we’ve discussed before, your cells have many ways to prevent mutations from happening.  Cells use proofreading when duplicating DNA.  If a cell detects a mistake is made in phase G2, it self-destructs (apoptosis).  Your genetic code is degenerate. This means that there are multiple possibilities to make most of the amino acids. MUTATIONS

 Mutations will either change the individual DNA sequences, or an entire chromosome.  We will look at DNA mutations first. There are four types:  Substitution  Deletion  Insertion  Inversion MUTATIONS

 A substitution switches one DNA letter for another.  These are usually point mutations – mutations that only affect one letter!  Example: Original sequence: THE FAT CAT ATE THE RAT. Mutant sequence: THE FAT HAT ATE THE RAT. MUTATIONS

 Many point mutations are also silent mutations – they will NOT change the amino acids that are created.  Original sequence: AUG CCA GGG UGU Amino acids: Met – Pro – Gly - Cys  Mutant sequence: AUG CCC GGU UGU Amino acids: Met – Pro – Gly - Cys MUTATIONS

 A deletion removes one or more DNA letters at once.  These are always frameshift mutations – mutations that change how codons are divided.  Example: Original sequence: THE FAT CAT ATE THE RAT. Mutant sequence: THE FAT ATA TET HER AT. MUTATIONS

 An insertion adds one or more DNA letters at once.  These are also always frameshift mutations!  Example: Original sequence: THE FAT CAT ATE THE RAT. Mutant sequence: THE FAT WCA TAT ETH ERA T. MUTATIONS

 An inversion reverses a sequence of DNA letters.  These usually happen during mitosis (M phase), as chromosomes line up in metaphase.  Example: Original sequence: THE FAT CAT ATE THE RAT. Mutant sequence: THE FAT HTE TAT ACE RAT. MUTATIONS

 Remember, point mutations leave the same number of nucleotides.  In contrast, frameshift mutations either add or remove nucleotides.  Point mutation: AUG CGA UUA → AUG CUA UUA Met – Arg – Leu → Met – Leu – Leu  Frameshift mutation: AUG CGA UUA → AUG CGG AUU A Met – Arg – Leu → Met – Arg - Iso MUTATIONS

 Now we will look at chrmosomal mutations.  Mutations that affect ONLY ONE chrmosome: 1.Deletion 2.Duplication 3.Inversion MUTATIONS

 Now we will look at chrmosomal mutations.  Mutations that affect TWO chrmosomes: 1.Insertion 2.Translocation MUTATIONS

 Sometimes, there is an error when egg or sperm cells divide, resulting in too many or too few chromosomes.  How do you think this type of change would impact an organism? MUTATIONS: NON-DISJUNCTION EX: TRISOMY 21 (DOWN SYNDROME)