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Lesson Overview Mutations
What types of
mutations are you
familiar with?
Lesson Overview Mutations
Videos
• Bozeman Mutations: https://youtu.be/eDbK0cxKKsk
• Amoeba sisters mutations: https://youtu.be/GieZ3pk9YVo
• White board, mutations: https://youtu.be/qxXRKVompI8
• Cystic fibrosis story: https://youtu.be/-a-WHZoTX0E
• CF explained: https://youtu.be/FMAOEOmLoUE
• Cf story 2: https://youtu.be/ORURXnKjCso
• Huntington’s disease explained: https://youtu.be/4HgFUvVyHYQ
Lesson Overview Mutations
Terms to know
1. Mutations
2. Point mutations
3. Substitutions
4. Insertions
5. Deletions
6. Frameshift mutations
7. Chromosomal deletion, duplication, inversion, and translocation
8. Mutagens
9. Sickle cell disease
10.Cystic fibrosis
11.Huntington’s disease
12.Nondisjunction
13.Down syndrome
14.Polyploidy
Lesson Overview Mutations
Preview
• Review p. 148. Draw and explain the three main types of chromosomal mutations: deletion, duplication, inversion and translocation.
• Review p.328 (black bio book). Draw and explain the two main types of gene mutations: point mutations including; base substitution, missense mutations, nonsense mutations, insertions/deletions, and frameshift mutations.
Lesson Overview Mutations
Types of Mutations
Now and then cells make mistakes in copying their own DNA,
inserting the wrong base or even skipping a base as a strand
is put together.
These variations are called mutations, from the Latin word
mutare, meaning “to change.”
Mutations are heritable changes in genetic information.
Lesson Overview Mutations
Types of Mutations
All mutations fall into two basic categories:
Those that produce changes in a single gene are known
as gene mutations.
Those that produce changes in whole chromosomes are
known as chromosomal mutations.
Lesson Overview Mutations
Gene Mutations
• Mutations that involve changes in one or a few nucleotides are known as
point mutations because they occur at a single point in the DNA
sequence. They generally occur during replication.
• Point mutations include substitutions, insertions, and deletions.
Lesson Overview Mutations
Substitutions
In a substitution, one base is changed to a different base.
Substitutions usually affect no more than a single amino acid,
and sometimes they have no effect at all.
Lesson Overview Mutations
Insertions and Deletions
• Insertions and deletions are point mutations in which one base is
inserted or removed from the DNA sequence.
• If a nucleotide is added or deleted, the bases are still read in groups of
three, but now those groupings shift in every codon that follows the
mutation.
Lesson Overview Mutations
Insertions and Deletions
Insertions and deletions are also called frameshift mutations because
they shift the “reading frame” of the genetic message.
Frameshift mutations can change every amino acid that follows the point
of the mutation and can alter a protein so much that it is unable to
perform its normal functions.
Lesson Overview Mutations
Lesson Overview Mutations
Chromosomal Mutations
• Chromosomal mutations involve changes in the number or structure of
chromosomes.
• These mutations can change the location of genes on chromosomes
and can even change the number of copies of some genes.
• There are four types of chromosomal mutations: deletion, duplication,
inversion, and translocation.
Lesson Overview Mutations
Chromosomal Mutations
Deletion involves the loss of all or part of a chromosome.
Lesson Overview Mutations
Chromosomal Mutations
Duplication produces an extra copy of all or part of a
chromosome.
Lesson Overview Mutations
Chromosomal Mutations
Inversion reverses the direction of parts of a chromosome.
Lesson Overview Mutations
Chromosomal Mutations
Translocation occurs when part of one chromosome breaks off
and attaches to another.
Lesson Overview Mutations
Mutagens • Some mutations arise from mutagens, chemical or physical agents in
the environment.
• Chemical mutagens include certain pesticides, a few natural plant
alkaloids, tobacco smoke, and environmental pollutants.
• Physical mutagens include some forms of electromagnetic radiation,
such as X-rays and ultraviolet light.
Lesson Overview Mutations
Preview
• Go to p.147 and p.163
• Create a chart that lists the major symptoms of the following disorders:
A (p.163)
1. Cystic fibrosis
2. Huntington’s disease
3. Sickle cell disease
B (p.147)
1. Turners syndrome
2. Klinefelters syndrome
3. Down syndrome
Lesson Overview Mutations
Harmful Effects
• Sickle cell disease is a disorder associated with changes in
the shape of red blood cells. Normal red blood cells are
round. Sickle cells appear long and pointed.
• Sickle cell disease is caused by a point mutation in one of
the polypeptides found in hemoglobin, the blood’s principal
oxygen-carrying protein.
• Among the symptoms of the disease are anemia, severe
pain, frequent infections, and stunted growth.
Lesson Overview Mutations
Lesson Overview Mutations
Lesson Overview Mutations
Cystic Fibrosis
• Cystic fibrosis (CF)
• Most cases result from the deletion of just three bases in the gene for a
protein called cystic fibrosis transmembrane conductance regulator
(CFTR). As a result, the amino acid phenylalanine is missing from the
protein, causing the protein to fold improperly.
Lesson Overview Mutations
Cystic Fibrosis
• CFTR normally allows chloride ions (Cl−) to pass across cell
membranes.The loss of these bases removes a single amino acid—
phenylalanine—from CFTR, causing the protein to fold improperly.
• The misfolded protein is then destroyed.
Lesson Overview Mutations
Cystic Fibrosis
With cell membranes unable to transport chloride ions, tissues
throughout the body malfunction. Children with CF have serious
digestive problems and produce thick, heavy mucus that clogs their
lungs and breathing passageways.
Lesson Overview Mutations
Lesson Overview Mutations
Lesson Overview Mutations
Huntington’s Disease
• Huntington’s disease is caused by a dominant allele for a
protein found in brain cells.
• The allele for this disease contains a long string of bases in
which the codon CAG—coding for the amino acid
glutamine—repeats over and over again, more than 40
times.
• The symptoms of Huntington’s disease, namely mental
deterioration and uncontrollable movements, usually do not
appear until middle age.
• The greater the number of codon repeats, the earlier the
disease appears, and the more severe are its symptoms.
Lesson Overview Mutations
Huntington’s Disease
Lesson Overview Mutations
Chromosomal Disorders
The most common error in
meiosis occurs when homologous
chromosomes fail to separate.
This mistake is known as
nondisjunction, which means
“not coming apart.”
Nondisjunction may result in
gametes with an abnormal
number of chromosomes, which
can lead to a disorder of
chromosome numbers.
Lesson Overview Mutations
Chromosomal Disorders
• If two copies of an autosomal chromosome fail to
separate during meiosis, an individual may be born with
three copies of that chromosome.
• This condition is known as a trisomy, meaning “three
bodies.”
• The most common form of trisomy, involving three
copies of chromosome 21, is Down syndrome, which is
often characterized by mild to severe mental retardation
and a high frequency of certain birth defects.
Lesson Overview Mutations
Chromosomal Disorders
• Nondisjunction of the X
chromosomes can lead to a disorder
known as Turner’s syndrome.
• A female with Turner’s syndrome
usually inherits only one X
chromosome.
• Women with Turner’s syndrome are
sterile, which means that they are
unable to reproduce. Their sex
organs do not develop properly at
puberty.
Lesson Overview Mutations
Chromosomal Disorders
• In males, nondisjunction may cause
Klinefelter’s syndrome, resulting from the
inheritance of an extra X chromosome,
which interferes with meiosis and usually
prevents these individuals from
reproducing.
• There have been no reported instances
of babies being born without an X
chromosome, indicating that this
chromosome contains genes that are
vital for the survival and development of
the embryo.
Lesson Overview Mutations
Beneficial Effects (Copy the definition)
• Plant and animal breeders often make use of “good” mutations.
• The condition in which an organism has extra sets of chromosomes is called
polyploidy.
• Polyploid plants are often larger and stronger than diploid plants.
• Important crop plants—including bananas and limes—have been produced this
way.
Quiz
1. Define base substitution.
2. Draw a picture of a chromosomal deletion.
3. Why is it called “Sickle” cell disease?
4. What are the symptoms of Huntington’s disease?
5. Draw the sex chromosomes of someone with Turner’s syndrome (first) and Klinefelter’s syndrome (second).