Answer 1:
This is a great question about genetics the
study of DNA and how it works. All living things
have a complete set of recipes in each cell.
Instead of being written on paper or stored in a
computer, the recipes are coded into a material
called DNA. Whether were cows or people,
we get our color from pigments. Our bodies make
the pigment using the recipes in our DNA. Some
recipes are slightly different, so one person, or
cow, may have red hair while another has black.
These differences in recipes are called mutations.
They happen when DNA is not copied exactly.
Every time a cell divides, it has to make a
complete copy of the DNA. Sometimes the copy is
not perfect. Each of your cells has TWO
copies of every recipe. One came from your mom.
One came from your dad. If the two recipes are
different, one is usually dominant, meaning that
we will see the product of that recipe. One will
usually be recessive, meaning that it is hidden.
For example, Holstein cattle are usually black and
white. Theres a recessive mutation that causes
them to be red and white instead. Because the
gene for black is dominant to the gene for red, a
cow with one recipe for black and one for red will
be black and white. She will only be red and
white if she gets the red recipe from both
parents. She has a 50/50 chance of passing on the
red gene to her calves. In cows, splotching
happens because, even though a hair follicle cell
has a recipe for color, it is switched off. This
means that the hair/fur and the skin under it have
no pigment. The skin looks pink because of the
blood vessels in it. The hair looks white. In
some breeds, the genes are switched off in
predictable areas. In others, such as the
Holstein, its random. In cows, the gene
for splotches is recessive to other genes,
including the one that gives Hereford cattle solid
red coats with white faces and bellies. Theres a
nice discussion of this, along with pictures, at
this site:
genes
Can you follow the authors reasoning about why
his solid-colored cows must have a copy of the
recessive gene? Another good discussion
of cow color is found at: animalscience
Thanks for asking, |
Answer 2:
Cows have splotches because their parents had
splotches, just like some kids have freckles
because their parents had freckles.They inherited
the coloration pattern. But not all cows have
splotches -- many types of cows are actually solid
colors. The splotches are caused by
pigmentation in the cows' cells, just like when we
see spots or freckles in people's skin.
Pigmentation is actually caused by many little
proteins that are colored. When you have a lot of
these tiny proteins in an area, you can see the
pigmentation with your eye. And speaking of your
eye -- the reason you have a dark spot in the
middle of the eye is because the cells in your eye
also have pigment proteins!
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