Download mutation PP

Mutation: DNA changes
DO NOW: 3/12
Objective:
Define mutation, identify several types, and
describe their effect on organisms.
Task:
1. If all mRNA molecules begin with the
sequence AUG, what DNA sequences
might be the beginning of a gene?
2 possibilities, in RED
5’ ATG CCC CAT 3’
• 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
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:
A.
B.
C.
D.
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:
A.
B.
C.
D.
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.
A.
B.
C.
D.
induced
inhibited
mutated
recombinant
Do you have it?
•
Mutations in which of the following cells
can be passed on to offspring?
A.
B.
C.
D.
Neurons (brain cells)
Epithelial (skin) cells
red or white blood cells
Germ (gonad) cells