Download 07. Mutations

Mutations
• Mutations – errors made in DNA
sequence that are inherited
• May have bad, good or no side effects
Types of Mutations
1. Silent Mutations – a mutation that does
not result in a change in the amino acid
coded for and therefore, does not
change the phenotype
 Also, since parts of your genes are noncoding, if the mutation happens in the
non-coding region, it may not have an
effect on the operation of the cell
 (P. 260)
2. Missense Mutations – a mutation that
results in the single substitution of one
amino acid in the resulting polypeptide
 Sickle cell anemia occurs from a
missense mutation
3. Nonsense Mutations – a mutation that
converts a codon for an amino acid into a
termination codon
 Only the part of the polypeptide before the
stop codon is produced, so once it hits the
stop codon, the rest of the polypeptide is
not made
 Often times these mutations are lethal to
the cell (it dies!)
• Silent, missense and nonsense mutations
arise from substitution of one base pair
for another
Frameshift Mutations
• When mutations change the reading
frame, they are called frameshift
mutations
• Deletion is a type of mutation that occurs
when one or more nucleotides are
removed from the DNA sequence (the
protein structure gets drastically changed,
resulting in a defective protein)
• Insertion is the placement of an extra
nucleotide in a DNA sequence, this also
shifts the reading frame (this will also
cause drastic changes to proteins)
• When thinking of frameshift mutations, if
one or two nucleotides are added/deleted,
this will cause a shift in the reading frame,
but if three are added/deleted, it will not
shift the reading frame (because amino
acids are coded with 3 codons, an amino
acid will be added or removed)
• Insertion and deletion mutations are
known as point mutations
• Point mutations are specific to one base
pair in the genome
• Translocation mutations involve large
segments of DNA and are the transfer of a
fragment of DNA from one site in the
genome to another location
• Translocation mutations can happen when
one chromosome breaks and loses a
piece and another chromosome breaks
and loses a piece. The pieces get
switched. This can result in a fusion
protein, with an altered function.
• Some types of leukemia are associated
with this.
• Transposable elements (jumping genes)
are segments of DNA that are moved as a
unit from one location to another on
chromosomal DNA
• If they fall in a coding region of a gene,
they will disrupt the transcription, leaving it
inactive
• Inversion is the reversal of a segment of
DNA within a chromosome, there is no
gain or loss in genetic material, but if the
break is in the wrong spot, it can disrupt
the gene
Causes of Genetic Mutations
• Spontaneous mutations occur without
chemical change or radiation but as a
result of errors made in DNA replication
• Mutagenic agents are things that can
cause a mutation. They are called
induced mutations because they are
caused by chemical agents or radiation
(e.g. UV radiation, cosmic rays, X rays,
certain chemicals)
• Read page 261 and 262 – “Causes of
Genetic mutations” and “Debate: Cell
Phones and Brain Cancer”
• Questions P. 263
• #1, 2, 3, 4, 5, 6, 7, 8, 9
• http://videos.howstuffworks.com/hsw/1041
8-molecules-and-evolution-types-ofgenetic-mutations-video.htm