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How do a few genes build a diversity of body parts?
There’s more in the genetic toolkit than just genes!
The Tools
GENES
HOX GENES
REGULATORY MOLECULES (Hox Proteins)
PROMOTOR REGIONS of DNA
GENETIC SWITCHES
Click your forward cursor to see how it works…
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•Turns out it takes more than just a GENE to
build a body
•And not everything outside the coding genes
is junk DNA
•PROMOTER REGIONS are associated with
genes and help initialize transcription of the
gene into a protein
•GENETIC SWITCHES play a role regulating the
EXPRESSION of genes
X
~ 98% of DNA is non-coding Junk DNA
~ 2% of DNA contains all the GENES
DNA
Promoter
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DNA HOX GENES are an important set of genes in
most animals. They are part of the genetic tool
box that regulates development of an organism.
Ribosome
HOX GENES are transcribed into
mRNA and then translated by the
ribosomes to form HOX
PROTEINS.
HOX PROTEINS then act as regulatory
molecules, or TRANSCRIPTION FACTORS,
that can promote or inhibit expression of
other genes.
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HOX PROTEIN
•RNA POLYMERASE is an enzyme in the cell
•It is essential in making mRNA to translate
into the amino acid sequence to form protein
•HOX PROTEINS also occur in the cell as
REGULATOR MOLECULES.
•When the right REGULATOR MOLECULE
becomes bound to the right GENETIC SWITCH
it can turn a gene ON (promote transcription)
or OFF (inhibit transcription)
DNA
Promoter
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BUT…
•Even though every cell in the
body contains the exact same
DNA with the same GENES
•Not every cell contains all the
same REGULATORY MOLECULES
•So only certain GENES might be
turned on, or EXPRESSED, in
certain types of cells
Promoter.
Promoter.
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•In the right type of cell…
•With the right REGULATORY MOLECULE
•To bind to the right GENETIC SWITCH
•A GENE can be turned ON
•In this case the regulator helps bring an
RNA POLYMERASE to the PROMOTOR
REGION to initialize mRNA transcription
•The gene is EXPRESSED
DNA
Promoter.
Click to continue
•In the right type of cell…
•With the right REGULATORY MOLECULE
•To bind to the right GENETIC SWITCH
•OR…
•With a different type of switch
•A GENE can be turned OFF
•In this case the regulator inhibits the
action of RNA POLYMERASE
•The gene is NOT EXPRESSED
DNA
Promoter.
Promoter.
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Now on to the rest of the exercise…
You’ll have a chance to try your
hand at regulating some gene
expression in arthropods!
Now that you understand the regulatory system that controls how genes are expressed,
revisit the example of wing differentiation between Drosophila and Butterflies.
Explain the genes and regulatory elements involved in the development of these wings:
Gene
1 set of wings
Large and flat
Has veins
No color
1 set of haltiers
Small and dense
Has veins
No color
1 set of wings
Large and flat
Has veins
Has color scales
1 set of wings
Large and flat
Has veins
Has color scales
T2
T3
T2
T3
Switches On / Off