They say that nothing in life is black and white.
For the zebra, though, it is all black and white stripes.
These stripes have given us traffic safety strategies, questionable fashion choices and
very interesting questions, one of which is whether a zebra is black with white stripes
or white with black stripes?
To answer this, we have to look at the body’s coloring paint—pigments!
Animals get their shades of browns, blacks, and reds as the result of a pigment called
melanin.
It comes in two broad varieties - eumelanin, which is responsible for the black and brown
colors, and pheomelanin, which lends the skin and hair yellow to reddish hues.
The pigment is produced by special cells called melanocytes, which are present in the outermost
layer of the skin, the epidermis.
The melanocytes make the pigment, which is then packed into small packets of pigment
called melanosomes.
These pigment packets are transported to skin cells, the keratinocytes, where the color
of the pigment shows up.
A similar process happens with hair.
Melanocytes associated with the hair root will deposit melanin to the cells that compose
our hair.
Where melanin isn’t produced, those areas turn white.
This is why people get white hair!
One way to prevent melanin being produced is to shut down the factory that produces
it.
Certain genes can be switched off to prevent melanocytes from maturing.
If they can’t mature, they won’t be able to produce melanin.
Thus, melanin production can be controlled by a few genes being turned on and off.
These genes not only produce enzymes that help make the melanin, but also control other
important activities, such as growth and how the cell packages the melanin.
When and how the gene switch is flipped is important in how stripes form in zebras.
We can now ask whether the genes in all the melanocytes are “on” by default and then
turned off in areas marked to be white stripes...
OR do the genes remain shut all over and they’re only switched on in those regions marked by
black stripes?
So, the answer is *drum roll*... the first one.
When scientists looked at tiny zebra fetuses as they developed, they observed that genes
related to melanin production were selectively switched off in those areas destined to become
white stripes, especially those involved in melanocytes maturing.
When the genes involved in this process are switched on and off, it results in the variety
in stripe pattern between different species of zebra.
Plain zebras have wider stripes, while mountain zebras have thinner stripes.
See the difference?
Depending on when, during the course of development, the genes are switched on and off, the stripe
patterns will form accordingly.
If this happens in the early stages of development, then the stripes will be thicker, as in the
plain zebra, and if it happens in later stages, the stripes will be thinner, as is found in
mountain zebras.
There are a host of genes involved in this process and scientists are still figuring
out precisely how stripes are formed, not only in zebras, but also in other animals,
like fruit flies and fishes.
While the puzzle is far from complete, genetic studies have revealed many genes and processes
that lead to a zebra’s black and white stripes.
Now, what about underneath the fur?
What’s the actual color of a zebra’s skin?
If you were to—hypothetically—shave a zebra, you’d find a black or brown hide
with no stripes.
The processes for skin pigmentation and hair pigmentation are different, so zebra skin
doesn’t have those iconic stripes.
I guess that just goes to show that, underneath it all, a zebra is really black with white
stripes.