What Darwin Never Knew
Part II

What are DNA switches and how do they work? Are they considered genes? If not genes, what is
their role in the development of an organism?
DNA Switches are not considered genes but when they are triggered (by body plan genes), they turn
on, and off, genes important to the development of an organism. They are used by body plan genes
to control when a gene expressed, as well as how intensely it is expressed.

How do the freshwater sticklebacks differ from ocean sticklebacks? What causes the difference
between the freshwater stickleback and the ocean stickleback?
Freshwater sticklebacks do not have the belly fins that are shaped like spikes found in ocean
sticklebacks. The freshwater stickleback has the gene for making spikes but they do not because of a
“broken switch.” The switch doesn’t work and thus does not turn on the gene for making spikes.

How is the loss of legs in the manatee related to what caused freshwater sticklebacks to lose their
belly spikes?
The scientists working on the loss of belly spikes on the stickleback also believe that the same
situation has occurred in the manatee. They think the manatee also has genes for making legs but
that the switch that triggers the making of legs is inactive.

How are DNA switches “thrown?” How can this explain the diversity of finches in the Galapagos
Islands?
DNA switches are “thrown” by body plan genes. The differences that exist among the Galapagos
finches’ beaks are not due to different genes coding for different beak types. The differences stem
from when certain genes, possessed by all of the finches, are activated. The time and intensity of
beak gene activation is dependent on when body plan genes throw the switches to activate the beak
genes.