Hailey MacDonald November 19th 2017 Writing Assignment 4
Mittens or Gloves?
There is no denying the appreciation and usefulness humans have for digits, fingers. It is
a main separating factor between humans and other mammals. What we might not think about is how important the timing of the production of digits are. Although it is a complex process, in theory has been explained more simply by Alan Turing’s using his mathematical model, A Turing- Type Mechanism.
The basic idea behind this model is there are two chemicals. One of the two chemicals is called the activator meaning it turns things on. Specifically, the activator found in mice embryos is fgf. The other of the two chemicals is the inhibitor known as Gli3 in mice, which turns things off. In this case, it stops the production of digits. At first, these two chemicals fluctuate randomly at similar levels. The activator is turned on, it then turns on the inhibitor which quickly turns the activator off. As seen in the figure below, the activator builds up which also causes the inhibitor to build up. Eventually the inhibitor has a high enough concentration to severely limits the amount of activator and turning digit development off. The two chemicals together work to create a wave like pattern. This pattern is what gives us the spaces in-between our fingers. The activator triggers digit development, and the inhibitor is what gives us these negative spaces
between each finger.
What controls this pattern is the Hox genes, or more specifically the distal Hox genes (distal meaning far away, our digits are furthest away from our bodies). Hox genes are what control the body plan of the embryo on the anterior-posterior (head- tail) axis. The amount of distal hox genes being expressed controls the digit formation by starting the self-regulating loop between the activator and inhibitor.
In order to determine what controls the normal digit formation, mutants, or mice with more and skinner fingers than normal mice were observed. This is known as polydactyl. Something went wrong in the timing or development of the digits causing an abnormal amount of digits to form.
The mutants in which the inhibitor, Gli3 was not expressed showed increased number of digits until the digits began to fuse together in a
mitten- like structure. This can be seen in the figure to the left. The less Gli3 that inhibits the activator that produces digit development, the more digits form and the skinner these digits are
K. (2011, January 13). Alan Turing’s Reaction-Diffusion Model – Simplification of the
Complex. Retrieved November 19, 2017, from