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MUTATIONS
Mutations are errors made in the DNA sequence that are inherited
These errors may have deleterious side effects, no effect, or positive side effects for an
organism
Errors made may change the protein and if the protein is essential for the cell structure or
metabolism then the outcome can be a damaged or even a dead cell
Types of Mutations
1. silent mutation
 has no effect on the cell; it occurs usually in the noncoding regions (introns) of the DNA,
that could be cut out and never show up
 can also be caused by the redundancy in the genetic code (different triplets code for the
same amino acid)
2.
missense mutation
 involves a substitution that results in a different aa being placed in the sequence
 ex/ sickle cell anemia
3.
nonsense mutation
 involves a change in the DNA sequence that causes a stop codon to replace a codon for an
aa; only the part of the protein prior to the stop codon will be produced.
 they are often lethal to the cell.
Frameshift Mutations
 Frameshift mutations are caused by insertions (an extra nucleotide is inserted) or
deletions (one or more nucleotides are removed from the DNA sequence (see Fig.1, p.260)
 If a frameshift mutation happens to insert one or two nucleotides, it can have devastating
effects because every amino acid in the polypeptide chain
 If a frameshift mutation inserts three nucleotides, it will just insert an extra amino acid
into the chain
Point Mutations
 Point mutations are caused by a substitution (the wrong base pair is substituted for the
correct one)
 Point mutations can be silent, missense or nonsense
 See Fig.1, p.260
Chromosomal Changes
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Translocation is when a part of one chromosome is exchanged with another nonhomologous
chromosome.
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Ex/ Chromosome 14 may get a segment from chromosome 8, who gets a segment from
chromosome 14 (a form of cancer results).
Inversion is when a gene segment is separated then inserted in reverse; no loss in genetic
material but the gene may be disrupted or come under transcriptional control.
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changes in chromosome structure have helped humans evolve.
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out of the 23 pairs of chromosomes we have 18 that are almost identical to those of
chimpanzees and gorillas and the other 5 are different only because of inversions or
translocations.
Transposable Genes
 discovered by Barbara McClintock
 fragments of DNA that move from one location to another
 may cause a disruption in transcription if they fall within a coding region
Causes of Genetic Mutations
 spontaneous mutations are caused by errors in the genetic machinery
 Ex/ DNA Polymerase I misses a point mutation
 induced mutations are a result from exposure to mutagenic agents (agents that can alter the
structure of DNA.)
 Ex/ ultraviolet radiation, X rays, and chemicals
Seatwork
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