Friday, April 06, 2007

Big Dogs and Little Dogs...

I always use dogs as an example to illustrate the power of selection combined with mutation to bring about new forms of organisms. Yes we are talking about evolution here. But one thing I really hadn't thought about is that dogs show more variability in mature height then any other land mammal.

Now researchers have identified a gene responsible for the great variation in dog height; see here and here. The researchers led by Elaine Ostrander (link to her lab home page)first studied the DNA of Portuguese water dogs. They chose this breed because the breed standard allows for greater ranges of heights than do the standards of other breeds. The small Portuguese water dogs had one variant of a gene called IGF1 related to the production of a protein called insulin like growth factor while larger Portuguese water dogs had other variants of this gene.

What was really interesting is that when they examined other breeds, small breeds apparently have the same variant of this gene while larger dogs have other variants. Also wolves, the ancestor of the domestic dog do not have much size variation and do not have the small dog variant of this gene.

You must be thinking so what? First of all it illustrates again how even single gene changes can lead to big changes in phenotype, so this research is important in understanding evolution. Next, humans also have the IGF1 gene and protein and it crops up in some interesting places. For instance variants of this gene are associated with prostate cancer and related to glucose metabolism in the developing brain.

Other Links:

Fact sheet on insulin like growth factor in medicine

Dog Genome home page

Portuguese Water Dog Club of America

New York Times Article about IGF1 and Dogs

NPR story link(includes Audio report)

Article on the role of IGF1 in growth

Article on the link between IGF1 and Prostate cancer

An article about population genetics of dogs.

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