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MUTATIONS
Are they good or bad?
Vocab you should know…
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Mutation: change in the nucleotide-base
sequence of a gene or DNA molecule
Deletion: loss of a part of DNA from a
chromosome
Inversion: reversal in the order of genes, or
of a chromosome segment, w/in a
chromosome
More vocab…
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Translocation: movement of a segment of
DNA from one chromosome to another,
which results in a change in the position of
the segment
Nondisjunction: failure of homologous
chromosomes to separate during meiosis I or
the failure of sister chromatids to separate
during mitosis or meiosis II
Mutation basics
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Mutations are any change/“error” in DNA
replication
DNA replication is very accurate
The enzyme DNA polymerase “proofreads”
the copied DNA & repairs most mutations
Mutations can be harmful, beneficial or have
no effect at all
More basics…
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Some mutations are caused by carcinogens
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i.e. uv light, radiation, toxins
Mutations that affect genes that control cell
division lead to cancer b/c cancer is a tumor
in which the cells begin dividing at an
uncontrolled rate & become invasive (they
spread out)
Germ-Cell Mutations
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Occur in the gametes
Don’t affect the organism itself
Can be passed on to offspring during
reproduction
Somatic-Cell Mutations
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Occur in the body cells
Can affect the organism
i.e. cancers
Cannot be inherited b/c they are not found in
the gametes
Lethal Mutations
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Often cause death, often before the
organism is born
Some can be beneficial – these are how
natural selection occur (the organisms w/
beneficial mutations reproduce more often &
spread that trait to their offspring)
Chromosome Mutations
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Deletion: loss of a
piece of chromosome
Deletion Mutation – Rieger Syndrome
Chromosome Mutations
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Inversion:
section of
chromosome
breaks off &
reattaches
backwards
Inversion Mutation – Hunter Syndrome
Chromosome Mutations
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Translocation: piece of
chromosome
breaks off &
attaches to a
nonhomologous
chromosome
Chromosome Mutations
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Nondisjunction: chromosome fails to
separate from its homologue during meiosis;
resulting in one gamete receiving an extra
copy of the chromosome (3 total) & another
receiving none
Nondisjunction – Down Syndrome
Trisomy 21
Down Syndrome cont’d
Mutation Quiz
1.
2.
3.
4.
5.
Any error in DNA replication is a/an _____.
What enzyme proofreads DNA & fixes most
errors?
What type of mutation occurs in gametes?
Why are somatic-cell mutations not
inheritable?
A _______ mutation is when a chromosome
losses a piece of itself.
Mutation Quiz Cont’d
6.
7.
8.
When part of a chromosome breaks off &
reattaches backwards it is a ____ mutation.
When a part of a chromosome breaks off &
attaches to another chromosome it is a
______ mutation.
When a chromosome fails to separate from
its homologue it is a _______ mutation.
Mutation Quiz Cont’d
During nondisjunction one cell receives ___
copies of the chromosome, while another
cell receives __.
10. Draw one of the phases of mitosis & label
it.
9.