UCSB Science Line
Sponge Spicules Nerve Cells Galaxy Abalone Shell Nickel Succinate X-ray Lens Lupine
UCSB Science Line
How it Works
Ask a Question
Search Topics
Our Scientists
Science Links
Contact Information
Why do cows have splotches?
Question Date: 2011-08-23
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:


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:


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!

Click Here to return to the search form.

University of California, Santa Barbara Materials Research Laboratory National Science Foundation
This program is co-sponsored by the National Science Foundation and UCSB School-University Partnerships
Copyright © 2020 The Regents of the University of California,
All Rights Reserved.
UCSB Terms of Use