Sunday, April 08, 2007

“Big Dog! Big Dog! Bow Wow Wow!”

A Single IGF1 Allele Is a Major Determinant of Small Size in Dogs. 2007. N.B. Sutter, et al. Science 316: 112-115.

Scientists have identified a piece of doggy DNA that reduces the activity of a growth gene, ensuring that small breeds stay small.
From the press release:

The small piece of DNA is not a gene, but is known as a regulatory sequence. It is located on dog chromosome 15 next to a previously known gene named IGF1, for insulin-like growth factor 1. The gene and regulatory sequence together are known as a haplotype or variant, and that haplotype was found in all breeds of small dogs, showing it is a major contributor to body size in all small dogs.

The IGF1 gene’s hormone helps humans and other mammals grow from birth to adolescence. But in small dogs, one or more mutations in the DNA next to the IGF1 gene suppress the gene’s activity, keeping small dogs from growing larger.

Medium and large dogs also have the IGF1 gene, but they do not have the same piece of DNA next to it, so their size is not restricted by that DNA.

Dogs evolved from wolves sometime before 12,000 to 15,000 years ago, when they were domesticated by humans. Because the small-dog genetic material is found in small breeds that are distantly related and found in distant regions, the researchers concluded the genetic instructions to make dogs small must be at least 12,000 years old.

Krypto & the S.P.C.A. © DC Comics
Most small dogs also are yappy, but Chase says: "Yappy we didn’t study."
Thanks to Dial B For Blog for the images!