The Genetics of Breed Dog Size
The IGF1 Gene Explains Why Dogs Come in Different Sizes
Dogs come in lots of shapes and sizes. Scientists have figured out that the IGF1 gene is one of the main reasons why.
There are over 400 different breeds of dog in the world that come in all different shapes and sizes. Since most of these breeds have come about in the last few hundred years, scientists predicted that all dogs would be genetically very similar to one another.
Back in 2004 scientists sequenced the first dog’s genome. Since then they have sequenced the DNA of many other breeds of dog and compared them to each other. What they have found is that all dogs came from the Asian gray wolf and that one dog’s DNA looks a lot like another dog’s DNA.
Sometimes it is hard to believe that a Chihuahua and a Great Dane are closely related. But they are. As are poodles and pit bulls, Shih Tzu and sheepdogs, etc.
Dogs Come in Different Sizes Because of the IGF1 Gene
The fact that all dog DNA is similar makes it easier for scientists to figure out where the differences come from. Scientists took advantage of this fact to determine why dogs come in such different sizes.
In April of 2007, a team of researchers figured out that the IGF1 gene was responsible for the different breed sizes. This result is both expected and surprising.
That the IGF1 gene is involved isn’t surprising. It has been shown to affect an animal’s size in other mammals. For example, mutations in the IGF1 gene can make mice smaller. The same is true in people.
What was surprising is that one gene can explain so much of a dog’s size. Body size in mammals is usually the result of many genes all working together. Certainly human height works this way. Because of this, scientists thought they would have to find many genes to explain the difference in size between different sized breeds. But this one gene explains these differences.
IGF1 Does Not Explain Size Differences within a Breed
IGF1 explains a lot about dog size but not everything. It cannot explain why, for example, some German Shepherds are bigger than other German Shepherds. Almost certainly other genes are involved in determining this difference.
These differences within a breed are probably determined similarly to how human height is. Many genes plus environmental effects result in a final dog size. But the average size between breeds is determined by IGF1.
Scientists will continue to study dogs’ DNA to figure out how such wildly different breeds came from a single DNA pool. The power of mixing and matching various versions of 25,000 genes is amazing. So too is the power of natural selection.
