Studying the new sequence of the canine genome shows how tiny genetic changes can create enormous variation within a single species.

Most dog breeds have only been in existence for a few hundred years.

In this article I highlight first our current understanding of what a dog breed really is and summarize the status of the canine genome sequencing project. I review some early work made possible by this project: studies of the Portuguese water dog, which have been critical to our understanding of how to map genes controlling body shape and size, along with studies aimed at understanding the genetics of muscle mass.