Download Controls Over Genes

Gene Control of Eukaryote Development
 Homeotic
Genes
 Type
of master gene that controls formation of specific body
parts during development
• Eyeless gene
• Normal
• No eyes form if there is a
mutation in the eyeless gene
• Antennapedia
• Expressed in the thorax causes
legs to form
• Expressed in the head causes
legs to form there also
• Eyes form wherever the gene
is expressed
Gene Control of Eukaryote Development

Flower formation
 Whether
a plant produces a leaf or a flower is
controlled by three floral identity genes (A, B, and C)
 Switched
on by environmental cues (seasonal change, length
of night, etc.)
 Four
different tissues form layers of whorls at the tip of a
shoot
 Each
produces one type of floral structure
 The
pattern is dictated by sequential, overlapping
expression of the ABC genes.
A
only = sepals
A
+ B = petals
B
+ C = stamens (pollen producing)
C
only = carpels (ova producing)
Gene Control in Prokaryotes
 Prokaryotic
step
cells use operons to control multiple genes in one
 One
“switch” is used to turn on or off a series of genes whose
products are used for the same overall process
 lac
Operon
 Used
by bacteria to break down lactose a disaccharide found in
milk
 Consists of
 three
genes in tandem which are involved in breaking down lactose
 a control region
Promoter: a binding site for RNA polymerase
 Operator: a binding site for a repressor protein

Gene Control in Prokaryotes
 lac
Operon
 Lactose
isn’t always available
 Bacteria
need to keep the genes turned off when no lactose is
available, but turned on when lactose is available
 Absence
A
of lactose
repressor binds to the operator
 Makes
 No
the promoter unavailable for RNA polymerase
transcription occurs
Gene Control in Prokaryotes
 lac
Operon
 Presence
 Some
of lactose
lactose is converted to allolactose
 Allolactose
 Changed
 The
binds to the repressor changing its shape
repressor protein no longer binds the operator
promoter is available for RNA polymerase to bind
 Transcription
proceeds
Gene Control in Prokaryotes
 lac
Operon
 Presence
of lactose
 Expression
of genes 1-3 results in the breakdown of lactose
 As
the concentration of lactose decreases, allolactose releases the
repressor
 The
repressor binds to the operator again inhibiting expression of the
three genes
Gene Control in Prokaryotes
 Demonstration
 Bacteria
of Operon control in prokaryotes
can be “transformed” by DNA cloning plasmids that
have genes from other organisms
Gene Control in Prokaryotes
 Demonstration
 Transformation
 Suspend
of Operon control in prokaryotes
of bacteria
bacteria in Transformation solution
 Solution
helps the DNA to enter the bacterial cells
Gene Control in Prokaryotes
 Demonstration
 Transformation
 Add
of Operon control in prokaryotes
of bacteria
plasmid DNA
 Small
circular piece of DNA containing genes and gene control regions
Gene Control in Prokaryotes
 Demonstration
 Transformation
 Add
of Operon control in prokaryotes
of bacteria
plasmid DNA: pGLO plasmid
 Ori:
origin of replication which ensures that the bacteria make multiple copies of
the plasmid
Gene Control in Prokaryotes
 Demonstration
 Transformation
 Add
of Operon control in prokaryotes
of bacteria
plasmid DNA: pGLO plasmid
 araC:
Arabinose operon regulatory protein