One small gene one BIG difference!!!

Sick of the large size? Turn them small!!

Scientists have being trying to find the genetic explanation for the extreme size variation in domestic dogs, as they believe the cause is due to intensive artificial selection. Surprisingly, a recent study showed that the small size in dogs was contributed simply by a single haplotype IGF-1. Since small size dogs do not seem to have a clear advantage over larger ones in the wild, the study suggests that artificial selection maintains this haplotype in the gene pool.

The IGF-1 gene, insulin-like growth factor–1, encodes the protein which plays an important role for muscle and skeleton development. In almost all smaller sized dogs, a special mutated sequence of DNA, called the regulatory sequence, was discovered to link to this IGF-1 gene. This regulatory sequence appears to limit the production of the protein during the critical growth period resulting in the small size. In larger dogs, the same regulatory sequence was not found and hence there was no restriction to their growth.

This discovery in canines provides some information about the genetic programming in our own skeleton. The genetic information discovered also contributes to the understanding of relative diseases such as cancer, the sign of uncontrolled cell growth. Furthermore, the result in the study could provide a precedent for studies aiming at identifying the genetic basis for complex traits such as behaviour and skeletal morphology.

Tzu-man Hung

Student no. :41767762

Primary Reference

Henderson, M., 2007, Scientists track down the gene that turns Great Dane into a Chihuahua, Time online,

http://www.timesonline.co.uk/tol/news/uk/science/article1620636.ece

Secondary Reference

Sutter, N.B., Bustamante, C.D., Chase, K., Gray, M.M., Zhao, K., Zhu, L., Padhukasahasram, B., Karlins, E., Davis, S., Jones, P.G., Quignon, P., Johnson, G.S., Parker, H.G., Fretwell, N., Mosher, D.S., Lawler, D.F., Satyaraj, E., Nordborg, M., Lark, K.G., Wayne, R.K., Ostrander, E.A., 2007, A Single IGF1 Allele is a major determination of smaller size dogs, Science, vol.316, p112-115.

Online access: http://www.sciencemag.org/cgi/content/full/sci;316/5829/1284b