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Biology
Biology
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12–4 Mutations
12-4 Mutations
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12–4 Mutations
12-4 Mutations
What are mutations?
Mutations are changes in the genetic
material.
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12–4 Mutations
Kinds of Mutations
Kinds of Mutations
Mutations that produce changes in a single gene
are known as gene mutations.
Ex) sickle cell disease, Huntington's Disease, cystic fibrosis
Mutations that produce changes in whole
chromosomes are known as chromosomal
mutations.
Ex) Down Syndrome, Turner Syndrome
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Kinds of Mutations
Gene Mutations
Gene mutations involving a change in one or a few
nucleotides are known as point mutations
because they occur at a single point in the DNA
sequence.
Point mutations include substitutions, insertions,
and deletions.
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12–4 Mutations
Kinds of Mutations
Substitutions usually
affect no more than a
single amino acid.
Ex) Sickle Cell Disease
is a replacement of A
by T on a specific gene
for hemoglobin
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12–4 Mutations
Kinds of Mutations
The effects of insertions or deletions are more
dramatic.
The addition or deletion of a nucleotide causes a shift
in the grouping of codons.
Changes like these are called frameshift mutations.
Changes the type/order of amino acid => alters protein structure
Ex) Tay-Sachs disease. Buildup of fatty acid around nerves
causes children to become blind and deaf and die by age 5. No cure, no
treatment.
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12–4 Mutations
Kinds of Mutations
Frameshift mutations may change every amino acid
that follows the point of the mutation.
Frameshift mutations can alter a protein so much that
it is unable to perform its normal functions.
Remember: The insertion or deletion of a single
amino acid can cause a frameshift mutation.
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12–4 Mutations
Kinds of Mutations
In an insertion, an
extra base is inserted
into a base sequence.
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12–4 Mutations
Kinds of Mutations
In a deletion, the loss of a single base is deleted and
the reading frame is shifted.
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12–4 Mutations
Kinds of Mutations
Chromosomal Mutations
Chromosomal mutations involve changes in the
number or structure of chromosomes.
Chromosomal mutations include deletions,
duplications, inversions, and translocations.
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12–4 Mutations
Kinds of Mutations
Deletions involve the loss of all or part of a
chromosome.
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12–4 Mutations
Kinds of Mutations
Duplications produce extra copies of parts of a
chromosome.
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12–4 Mutations
Kinds of Mutations
Inversions reverse the direction of parts of
chromosomes.
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12–4 Mutations
Kinds of Mutations
Translocations occurs when part of one
chromosome breaks off and attaches to another.
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12–4 Mutations
Significance of Mutations
Significance of Mutations
Many mutations have little or no effect on gene
expression.
Some mutations are the cause of genetic
disorders.
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12–4 Mutations
Significance of Mutations
Beneficial mutations may produce proteins with new
or altered activities that can be useful.
Wikipedia: For example, a specific 32 base pair deletion in human CCR5 (CCR5-Δ32) confers
HIV resistance to homozygotes and delays AIDS onset in heterozygotes.[9] The CCR5
mutation is more common in those of European descent. One theory for the etiology of the
relatively high frequency of CCR5-Δ32 in the European population is that it conferred
resistance to the bubonic plague in mid-14th century Europe. People who had this mutation
were able to survive infection; thus, its frequency in the population increased.[10] It could also
explain why this mutation is not found in Africa where the bubonic plague never reached.
Newer theory says the selective pressure on the CCR5 Delta 32 mutation has been caused
by smallpox instead of the bubonic plague
Polyploidy is the condition in which an organism has extra
sets of chromosomes.
Most common in plants
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A mutation in which all or part of a chromosome
is lost is called a(an)
a. duplication.
b. deletion.
c. inversion.
d. point mutation.
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A mutation that affects every amino acid
following an insertion or deletion is called a(an)
a. frameshift mutation.
b. point mutation.
c. chromosomal mutation.
d. inversion.
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A mutation in which a segment of a chromosome
is repeated is called a(an)
a. deletion.
b. inversion.
c. duplication.
d. point mutation.
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The type of point mutation that usually affects
only a single amino acid is called
a. a deletion.
b. a frameshift mutation.
c. an insertion.
d. a substitution.
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When two different chromosomes exchange
some of their material, the mutation is called
a(an)
a. inversion.
b. deletion.
c. substitution.
d. translocation.
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END OF SECTION
Biology
Biology
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12-5 Gene Regulation
Fruit fly chromosome Mouse chromosomes
12-5 Gene Regulation
Fruit fly embryo
Mouse embryo
Adult fruit fly
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Adult mouse
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12-5 Gene Regulation
Gene Regulation: An Example
Gene Regulation: An Example
E. coli provides an example of how gene
expression can be regulated.
An operon is a group of genes that operate
together. (some operons turn genes off or on)
In E. coli, these genes must be turned on so the
bacterium can use lactose as food.
Therefore, they are called the lac operon.
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12-5 Gene Regulation
Gene Regulation: An Example
How are lac genes turned off and on?
The lac genes are turned off by repressors
and turned on by the presence of lactose.
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12-5 Gene Regulation
Gene Regulation: An Example
On one side of the operon's three genes are two
regulatory regions.
• In the promoter (P) region, RNA polymerase
binds and then begins transcription.
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12-5 Gene Regulation
Gene Regulation: An Example
• The other region is the operator (O).
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12-5 Gene Regulation
Gene Regulation: An Example
When the lac repressor binds to the O region,
transcription is not possible.
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12-5 Gene Regulation
Gene Regulation: An Example
When lactose is added, sugar binds to the repressor
proteins.
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12-5 Gene Regulation
Gene Regulation: An Example
The repressor protein changes shape and falls off the
operator and transcription is made possible.
Lactose causes the lac gene to turn on!!
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12-5 Gene Regulation
Gene Regulation: An Example
Many genes are regulated by repressor proteins.
Some genes use proteins that speed transcription.
Sometimes regulation occurs at the level of protein
synthesis.
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12-5 Gene Regulation
Eukaryotic Gene Regulation
How are most eukaryotic genes
controlled?
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12-5 Gene Regulation
Eukaryotic Gene Regulation
Eukaryotic Gene Regulation
Operons are generally not found in
eukaryotes.
Most eukaryotic genes are controlled
individually and have regulatory
sequences that are much more complex
than those of the lac operon.
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12-5 Gene Regulation
Eukaryotic Gene Regulation
Many eukaryotic genes have a sequence called the
TATA box.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
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12-5 Gene Regulation
Eukaryotic Gene Regulation
The TATA box seems to help position RNA
polymerase.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
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12-5 Gene Regulation
Eukaryotic Gene Regulation
Eukaryotic promoters are usually found just before
the TATA box, and consist of short DNA sequences.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
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12-5 Gene Regulation
Eukaryotic Gene Regulation
Genes are regulated in a variety of ways by enhancer
sequences.
Many proteins can bind to different enhancer
sequences.
Some DNA-binding proteins enhance transcription
by:
• opening up tightly packed chromatin
• helping to attract RNA polymerase
• blocking access to genes.
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12-5 Gene Regulation
Development and Differentiation
Development and
Differentiation
As cells grow and divide,
they undergo
differentiation, meaning
they become specialized in
structure and function.
Hox genes control the
differentiation of cells and
tissues in the embryo.
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12-5 Gene Regulation
Development and Differentiation
Careful control of expression in hox genes is
essential for normal development.
All hox genes are descended from the genes of
common ancestors.
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Development and Differentiation
Hox Genes
Fruit fly chromosome Mouse chromosomes
Fruit fly embryo
Mouse embryo
Adult fruit fly
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Adult mouse
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Which sequence shows the typical organization
of a single gene site on a DNA strand?
a. start codon, regulatory site, promoter, stop
codon
b. regulatory site, promoter, start codon, stop
codon
c. start codon, promoter, regulatory site, stop
codon
d. promoter, regulatory site, start codon, stop
codon
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A group of genes that operates together is a(an)
a. promoter.
b. operon.
c. operator.
d. intron.
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Repressors function to
a. turn genes off.
b. produce lactose.
c. turn genes on.
d. slow cell division.
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Which of the following is unique to the regulation
of eukaryotic genes?
a. promoter sequences
b. TATA box
c. different start codons
d. regulatory proteins
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Organs and tissues that develop in various parts
of embryos are controlled by
a. regulation sites.
b. RNA polymerase.
c. hox genes.
d. DNA polymerase.
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