Mutation: DNA changes DO NOW: 3/12 Objective: Define mutation, identify several types, and describe their effect on organisms. Task: If all mRNA molecules begin with the sequence AUG, what DNA sequences might be the beginning of a gene?

5’ ATG CCC CAT 3’ 2 possibilities, in RED Read as a coding strand (5’3’) ATG transcribed to AUG. Read as a template strand (3’5’), TAC translates to AUG.

UPDATE! Bio3: FlyDay VI, Seminar TOMORROW Reports due at end of seminar Pedigrees Squares Conclusions Handouts Show up prepared to defend your results and think on your feet!

Back to the DNA… Refresher: Replication Transcription Translation DNA mRNA Protein

Transcription: DNA  mRNA The information carried by DNA is copied into mRNA form by the enzyme RNA polymerase (and others). Translation: mRNA  Protein The information carried by mRNA is translated into a sequence of amino acids. This requires a ribosome (containing rRNA) and tRNA to bring the correct amino acids to the mRNA

DNA changes Sometimes, a gene can be “turned on” (induced, or activated) and cause a protein to be made, while at other times it can be “turned off” (inhibited or repressed) to save energy - like a light bulb Genes also change over time, like people do. A mutation is a change in a DNA sequence.

MUTATION: A Change in a DNA Sequence Any change to a DNA sequence is a mutation. Therefore, a MUTANT is an organism with a DNA sequence that has changed… meaning all of us! Very few mutations are advantageous, some are harmful, but most make no difference at all (silent mutations), since about 90-95% of your DNA does not code for proteins. Note: only mutations present in gametes can be passed on to offspring!

Pop-Culture Mutants?

Definitely Not This One…

Mutation Causes Replication errors (about 1/108, 1/1010 after error correction) Mutagens Chemicals that modify or mimic bases Radiation Retroviruses, transposons, gene splicing. Base analogs: 5-bromo-uracil can replace thymine in DNA, causing mutations because it can base-pair with guanine

Mutations Cause Variation in Populations Mutation produces new alleles that can give organisms new characteristics. Variation is ESSENTIAL for evolution to take place.

Mutant Flies

Gene Splicing and Transgenic Organisms Gene splicing is when genes from two or more organisms are combined to make a transgenic organism RECOMBINANT DNA: A DNA molecule with information from 2 or more organisms.

Mutation Type 1 Genome Mutations (nondisjunction): a change in chromosome number. Always serious, often lethal.

Mutation Type 2: Chromosomal Mutations Chromosomal mutations affect large pieces of chromosomes. Their effects vary. Examples: Deletion (A) Inversion (B) Translocation (C) Duplication (D)

Mutation Type 3: Single Gene Mutations As the name implies, single gene mutations affect only a single gene. .

Types of Single Gene Mutations Deletions: One or more bases is removed from a sequence. ATTAGG becomes ATGG Insertions: One or more bases is added. ATTAGG becomes ATTAAGG Point Mutations: One or more bases is replaced with a different base ATTAGG becomes ATAAGG

More Mutation Examples Missense: (point mutation) The cat ate the rat  The cat ate the hat Nonsense: (new stop signal) The cat ate the rat  The cat ate Frameshift: (insertion or deletion changes reading frame) The cat ate the rat  Ath eca tat eth era t.

Mutations that Matter Most mutations have no effect. Those that do have an effect are usually bad: Cancer Loss of function (protein doesn’t work anymore) A tiny fraction of a fraction have a positive effect Increased survival & reproduction (Michael Phelps Marfan Syndrome, etc…)

Do you have it? A mutation is: When a gene is turned on When a gene is turned off A change in a DNA sequence Always bad for the organism that has it

Do you have it? These types of mutations are the most serious because they can change the whole protein structure, not just one amino acid: Point mutations Frameshift mutations Insertions of 3 nucleotides Always bad for the organism that has it

Do you have it? The lac gene produces an enzyme that breaks down lactose (a type of sugar) and provides energy to a cell. The gene needs to be _____________ if lactose is to be used. induced inhibited mutated recombinant

Do you have it? Mutations in which of the following cells can be passed on to offspring? Neurons (brain cells) Epithelial (skin) cells red or white blood cells Germ (gonad) cells