Download Mutations - Biology R: 4(A,C)

Section 12-4
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Determining the Sequence of a Gene
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DNA contains the code of instructions for cells.
Sometimes, an error occurs when the code is
copied. Such errors are called mutations.
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Mutations may result in disorders, diseases,
changes in appearance, or they may have no
effect at all.
Changes in the DNA sequence that
affect genetic information
 Mistakes occur every now and then
 There are many different types of
mistakes:

› Inserting the wrong base
› Deleting a base
› Skipping a base
› Etc…
Gene mutations result from changes in a
single gene
 Chromosomal mutations involve
changes in whole chromosomes


Point mutations: mutations that affect
one nucleotide occurring at a single
point in the DNA sequence
› Substituting one nucleotide for another
generally change one of the amino acids in
a protein
In sickle celled anemia a
different protein is made
In cystic fibrosis a
stop codon is made
For example: DNA:
mRNA:
amino acids:
TAC-GCA-TGG-AAT
AUG-CGU-ACC-UUA
Met – Arg – Thr – Leu
The 2nd “C” in the DNA is substituted by a “T”
DNA:
TAC-GTA-TGG-AAT
mRNA:
AUG-CAU-ACC-UUA
amino acids:
Met – His – Thr – Leu

Frame-shift mutations: mutations that add or
remove a nucleotide, shifting the nucleotides
(“reading frame”) to make different codons
› Adding/removing one nucleotide affects every
amino acid following the insertion or deletion
severely altering the performance of the protein
› For example: THE FAT CAT ATE THE RAT
› Deletion of H:TEF ATC ATA TET HER AT
Nucleotides are added, so different proteins
are made, decreasing strength of muscles
For example: DNA:
mRNA:
amino acids:
TAC-GCA-TGG-AAT
AUG-CGU-ACC-UUA
Met – Arg – Thr – Leu
A “T” is added between the 1st A & C
DNA:
TAT-CGC-ATG-GAA-T
mRNA:
AUA-GCG-UAC-CUU-A
amino acids:
Ile– Ala – Tyr – Leu

There are four chromosomal mutations:
› Deletion: loss of all or part of a chromosome
› Duplication: segment of a chromosome is
repeated
› Inversion: orient part of chromosome in
reverse direction
› Translocation: part of one chromosome
breaks off and attaches to another, nonhomologous, chromosome.
Deletion
Duplication
Inversion
Translocation