The Evolution of Dachshunds’ Legs Offers Surprising Scientific Insights

In the ten to thirty thousand years since people domesticated dogs, the species has undergone dramatic change.  Indeed it is difficult to grasp the idea that dogs like the toy poodle and great dane descend from wild wolves, especially so recently in evolutionary history.  Like other domesticated animals, such as horses and cats, selective breeding significantly sped up differentiation between dog breeds. 

National Human Genome Research Institute (NHGRI) researchers have recently discovered a common origin for the disproportionately short and curved legs present in several dog breeds.  The charm of dachshunds and basset hounds largely lies in those short legs, which is a standard characteristic for almost 20 breeds.  The genetic condition, chondrodysplasia, is similar to the disproportionately short limbs found in the type of human dwarfism called hypochondroplasia.

Genetic analysis, published in Science, reveals that each of these dog breeds owe their iconic body style to a single evolutionary event, rather than developing the same appearance separately.  What really surprised the researchers was that the mutation was due to a retrogene being introduced to the dog genome.

Retrogenes are formed when the typical flow of information, DNA to mRNA to protein, is interrupted.  A retrogene is formed if mRNA information is ‘reverse transcribed’ back into DNA, typically by a retrovirus enzyme, and re-implanted into the genome.  This can cause problems with gene expression, either imcreasing protein production or producing the protein at the wrong time.  It is the later of the two that presents the mutation in the case of short legged dogs.

The retrogene in question is a duplicate copy of growth regulator FDF4.  The misplaced copy of FDF4 is thought to turn on certain growth receptors at the wrong time during fetal development.

This research has obvious significance to the veterinarian and dog breeder communities, but the impact of these findings will reach far beyond that narrow scope.  It was previously hypothesized that retrogenes could play a role in evolution, but this is the first documented case of a retrogene making such an important impact on development of a species.  It is doubtless that this discovery will jump-start a search for other examples of retrogene-mediated evolutionary change.

Additionally, this research may give new clues to scientists studying human dwarfism.  Two thirds of human hypochondroplasia cases are already shown to result from a mutation in FGFR3, but thus far there is no gene connected with the remaining cases.  FDF4 will certainly be researched as a possible culprit.