From the last Science Magazine…
Nathan B. Sutter, Carlos D. Bustamante, Kevin Chase, Melissa M. Gray, Keyan Zhao, Lan Zhu, Badri Padhukasahasram, Eric Karlins, Sean Davis, Paul G. Jones, Pascale Quignon, Gary S. Johnson, Heidi G. Parker, Neale Fretwell, Dana S. Mosher, Dennis F. Lawler, Ebenezer Satyaraj, Magnus Nordborg, K. Gordon Lark, Robert K. Wayne, and Elaine A. Ostrander
Science 6 April 2007: 112-115.
Small dogs are small because they carry a particular allele of the gene encoding insulin-like growth factor 1.
A short intro blurp they had for those who cannot access the full text…
(SCIENCE VOL 316 6 APRIL 2007, page 15)
Sizing Up Man?s Best Friend
In contrast to most mammalian species, Canis familiaris (the domestic dog) shows extreme diversity
in body size. Sutter et al. (p. 112, cover) show that a single allele of the gene encoding
insulin-like growth factor?1 (IGF-1) is shared by all small dog breeds but is nearly absent from
giant dog breeds, implying that sequence variation in the IGF-1 gene plays a causal role in dog
size. Discovery of the IGF-1 gene was facilitated by its localization within a genomic signature, or
haplotype block, that probably arose as a result of centuries of dog breeding by humans.