Transcript Mutation - Teacherpage

DNA Mutations
Chapter
12.4
Mutation
• Mutation: Any change in a gene is a mutation.
• Substances that cause a mutation are called
mutagens.
• Mutations can also happen spontaneously.
Point Mutation
• A change in one nucleotide
• Original:
The fat cat ate the wee rat.
Point Mutation: The fat hat ate the wee rat.
Point Mutation
• Base Substitution - One nucleotide is
replaced with another nucleotide.
ACC CUA GGC AUC AU
ACC UUA GGC AUC AU
“C” is substituted with “U”
Redundant Systems
• Sometimes these mutations have no effect!! Ex.
The codons of UCU, UCC, UCA, & UCG all code
for the amino acid Serine. Any substitution in
the third base of the codon has no effect.
• However, a substitution in the first or the
second base of the codon, changes the
code for the amino acid.
• UUU codon is for phenylalanine
• UCU codon is for serine
• CUU codon is for leucine
Frameshift Mutations
• Either the insertion or a deletion of a nucleotide
which results in a shift in the code and mistakes
from the point of mutation on.
• Original
• Frame Shift
The fat cat ate the wee rat.
The fat caa tet hew eer at.
Somatic Cell mutations
• Mutations happen in all
organisms, if it happens in a
somatic cell then only the
individual is affected.
Meiosis Mutations
• If it happens in a gamete then the
mutation is passed on to the
offspring.
Meiosis Mutations
• Mistakes during meiosis:
Mistakes during meiosis, such as
non-disjunction, can result in
three chromosomes instead of a
pair (trisomy) or more than three
(polyploidy).
Down’s Syndrome
• Trisomy in humans can result in birth defects
such as trisomy 21, or Down’s syndrome.
Quick Review
• Point mutations occur
as a result of a
change in one
nucleotide.
• The 2 basic types of
point mutations are
base substitutions
and frame shift.
Quick Review
• Substitution
mutations are the
result of one
nucleotide being
replaced by another.
This results in one
amino acid being
incorrectly coded.
Quick Review
• Frame shift mutations
are the result of
either a deletion or an
insertion of a
nucleotide. This
results in a mistake in
all the triplet codes
from the mutation on.
Gene Mutations
• Gene Mutations occur as a result of changes in
chromosomal fragments. There are four basic
types:
• 1. Translocation
• 2. Inversion
• 3. Insertion
• 4. Deletion
Gene Mutations
1.Translocations When part of one
chromosome breaks
off and is added to a
different
chromosome.
Gene Mutations
2. Inversion – When
part of a chromosome
breaks out and is
reinserted backwards.
Gene Mutations
3. Insertion
When part of a
chromatid breaks off
and attaches to its
sister chromatid.
The result is a
duplication of genes
on the same
chromosome.
Gene Mutations
4. Deletion
When part of a
chromosome is left
out.
Mutations & Evolution
• Mutations that have a
negative effect
usually result in the
loss of that mutation
due to the law of the
survival of the fittest.
Mutation & Evolution
• However, there are
times that the
mutations are
beneficial and result
in the evolution of the
species and increased
variation in the
population.
• We’ll learn much
more about this next
unit!!!