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Genetic Mutations
Mutations
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Mutations: changes in the DNA
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They may not change the individual in a way that
impacts their reproductive success or
They can be damaging.
We don’t get to choose which one.
Mutations can occur mainly in 3 ways:
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Spontaneously
Environmental exposure to mutagens (chemical,
radiation, etc.)
Inheritance: also called germ line mutations.
Hereditary mutations occur in the sex cells (sometimes
referred to as “germ cells”) and are therefore passed
on from parent to offspring.
Genetic Disorders
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A genetic disorder is a disease caused in whole or in part by a
"variation" (a different form) or "mutation" (alteration) of a gene.
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Single gene disorders: mutation in a single gene. The mutation
may be present on one or both chromosomes (one chromosome
inherited from each parent).
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Chromosome disorders: structural changes within chromosomes,
or excess or deficiency of the genes that are located on
chromosomes
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Ex. Sickle cell disease, cystic fibrosis and Tay-Sachs disease are
examples of single gene disorders.
Ex. Down syndrome, for example, is caused by an extra copy of
chromosome 21, but no individual gene on the chromosome is
abnormal.
Multifactorial inheritance disorders : combination of small
variations in genes, often in concert with environmental factors.
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Ex. Heart disease and most cancers are examples of these disorders.
Gene mutations
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These are mutations within a gene
A mutation that only changes one nucleotide
is called a point mutation.
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Substitution
Insertion
Deletion
Resulting proteins can be NOT MADE,
NONFUNTIONAL, or BETTER FUNCTIONING
Chromosome Mutation
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The gene’s
location can
change on a
chromosome
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This is a
structural
change
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Types of Mutations
Wild Type ”Normal”: ACT-GAA-CTG-ATT
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(Thr-Glu-Leu-Ile)
Substitution:
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(Thr-Asp-Leu-Ile)
Deletion:
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ACT-GA-C-TGA-TT
(Thr-Asp-Stop)
Inversion:
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ACT-GAA-CCT-GAA-CTG-ATT
(Thr-Glu-Pro-Gly-Leu-Ile)
Frameshift:
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ACT- - - CTG-ATT
(Thr-Leu-Ile)
Insertion:
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ACT-GAC-CTG-ATT
(Thr-Glu-Gln-Ile)
ACT-GGT-CAA-ATT
Causes of Mutation
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De novo – also called “new” or
“spontaneous” mutations, de novo
mutations occur in sex cells during or after
fertilization.
Somatic – also called acquired mutations,
these happen to individuals in their
lifetime. A mistake may be made when the
DNA is being copied to make new cells, or
via environmental damage, such as UV
radiation. Since only somatic (body) cells
are affected, such mutations cannot be
inherited.
Nondisjunction
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Nondisjunction is
a chromosome
disorder
It occurs when
either homologous
chromosomes fail
to separate during
anaphase I of
meiosis, or sister
chromatids fail to
separate during
anaphase II.
Nondisjunction
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The frequency of nondisjunction is quite
high in humans, but the results are
usually so devastating to the growing
zygote that miscarriage often occurs very
early in the pregnancy.
If the individual survives, he or she
usually has a set of symptoms - a
syndrome - caused by the abnormal
dose of each gene product from that
chromosome.
Normal Human Karyotype
Down syndrome (trisomy 21)
(Extra Chromosome 21)
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Down syndrome
affects 1:700 children
Characteristic facial
features, short
stature, heart defects,
susceptibility to
respiratory disease,
shorter lifespan
Often sexually
underdeveloped and
sterile, usually some
degree of mental
Typical Down Syndrome