Size differences between dogs come down to a single change in a single gene.

All dogs are members of the same species, and each characteristic breed is a result of selective breeding by humans. Now, scientists have found that the extreme differences in dog size – between say a Chihuahua and Great Dane – are largely determined by a single change in a single gene.

"A Single IGF1 Allele is a Major Determinant of Small Size in Dogs" by Nathan B. Sutter and others, Science (volume 316), April 6, 2007, pages 112-115.

Duration: 3 minutes

Posted: April 25, 2007

Dave Micklos: Welcome to DNA today. I'm Dave Micklos...

Jan Witkowski: ...and I'm Jan Witkowski. And we're here at Cold Spring Harbor Laboratory talking about DNA in the news.

DM: And today's new is about man's best friend – dog. Now, we all know that dogs come in many shapes and sizes, from teeny-tiny, yappy Chihuahua to that great, huge, lumbering Great Dane. Recent research has shown that one gene is, in fact, responsible for most of the difference between the size of a little tiny dog and a great huge one.

JW: I go to the Westminster Kennel club every year, so I am very familiar with seeing this vast range in dog size. Remarkably, of course, dogs are all the same species and yet they have this extreme range from the tiniest to the biggest. You're telling me it's a change in one gene that produces this?

DM: It seems to be. A group of researchers headed by scientists at the National Human Genome Research Institute sequenced the genes from small dogs and large dogs, and found that a difference of one letter in the genetic code in one gene, seems to determine most of the difference in size between the small and the large dogs. So, one version of the gene was present almost exclusively in the small dogs, but absent virtually in the small dogs.

JW: And this gene is a gene called Insulin-like Growth Factor-1, IGF-1, which, as its name suggests, is related to insulin. As we all know, insulin is very important in regulating blood sugar, regulating metabolism in general, and is known to be involved in regulating size in mammals.

DM: Yes, especially in bone and muscle growth, which, of course, account for size. The interesting thing about this mutation is that it looks as though it cropped up 12 or 14 thousand years ago, which was really before the close association with humans. So, the implication is, humans found several sizes of dogs around, quite big ones and quite small ones, and then accentuated those size differences as they bred different breeds for their uses.

JW: Now, size is not the only thing that distinguishes different breeds of dogs. They also differ in their behavior.

DM: Yeah, you don't want to be bitten by certain dogs.

JW: Does this research suggest that we might find genes for behavioral differences in dogs?

DM: Well, as you know, the ability to look for tiny differences in genes among lots and lots of living things is possible now. And almost certainly we'll see that some of the genes that help determine behavior will also have small changes, but in all likelihood, we're going to see that those small changes are not enough to produce behavior. In fact we have the environment, the training by the master, and so forth.