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Gene regulation
How does DNA make different cells?
• All cells have a
full set of DNA
• Not all the DNA is
expressed in each
one
• Promoters and
repressors allow
only certain genes
to be expressed
(make protein)
Nerve, cardiac, muscle, white blood cells
The gene that breaks down lactose is repressed
How it works
• When lactose is added, it binds to the
repressor protein.
Activation
Left side: why do
you think this
process is called a
“positive” feedback
loop?
When lactose binds to the repressor, it moves
away, allowing the protein to be made
Eukaryotic Gene Regulation
• Many eukaryotic genes have a sequence
called the TATA box that helps to position
RNA polymerase.
Direction of transcription
Differentiation
• From a fertilized egg to an
adult, cells grow and
divide.
• They also differentiate into
many different types of
cells
• Hox genes control that
differentiation
• They are inherited from
the genes of our common
ancestors
Gene mutation
• Point mutation: the subtraction, addition or substitution
of a single nucleotide
• Changing a nucleotide will change the codon
– Can change the amino acid
• Subtraction and addition can cause a “Frame shift”
making all amino acids downstream change
– This can completely change a protein
– Most mutations are harmful
Left side: why
don’t all mutations
causes changes to
the amino acids?
Not all mutations are equal
• If you put a hox gene for “eye”
from a fruit fly into a mouse
embryo, it will develop into an
mouse eye.
• If you move a hox gene for an
eye from the head to the back
of a fruit fly embryo the eye will
develop on the back
• Small genetic changes can
make large changes to an
organism.
Summary
review
1. What do hox
genes do?
2. What are
repressors and
promoters?
3. What causes a
frame shift?