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Researchers Discover Genetic Mutation Responsible For Short Legged Dogs

Researchers have discovered the genetic factor responsible for the odd-looking short legs in dogs like Dachshunds, Basset Hounds, Corgis and 16 other breeds. The findings of this study may turn out to be useful in understanding dwarfism in humans.

The study was led by a team from National Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH). The study was published in the online version of the Science journal.

How the study was carried out?
The researchers from NHGRI examined DNA samples from 95 short legged dogs, along with 740 other dogs. They surveyed more than 40,000 markers of DNA variation. They uncovered a genetic signature unique to short-legged dogs. Later, the researchers conducted DNA sequencing and computer analyses.

They found out that the dogs’ absurdly short legs can be traced back to one mutational event in the dogs’ DNA which occurred very early in the evolution of dogs. The short-legged dogs have an additional copy of gene which codes for a growth promoting protein known as Fibroblast Growth Factor 4 – FGF4.

Though these genes are functional, they lack certain important parts. This leads to a malfunction of the gene, resulting in short legs. Such genes are called retrogenes. The researchers believe that these retrogenes got inserted in the short-legged dogs’ DNA a little after modern dogs got separated from wolves.

Mechanism of the dog DNA mutation – How retrogenes are produced
Cells make proteins by using the DNA code responsible for producing protein. The DNA code is transcribed onto a particle and is known as messenger RNA (mRNA). The mRNA then moves to the cell’s surface. Here, molecules called ribosomes receive the code information and use it to make proteins.

small dogsSometimes, the mRNA comes across something (mostly a virus called retrovirus) that spins its back into the DNA. The DNA code might then get inserted in the wrong place in the genome. It might or might not be functional depending on where it gets inserted. If it is functional, it is known as retrogene.

Researchers theorize that in the when it comes to short-legged dogs, these retrogenes result in the over-production of FGF4. This may disturb the normal process of fetal development, such as turning on key development factors at the wrong time. This leads to short legs.

What one has to remember is that dogs like Dachshunds have ‘disproportionately short’ legs. Other dogs like miniature poodles also have short legs, but their bodies are also small. Dogs like Dachshunds have short legs but big bodies. Only dogs which have disproportionately short legs have a genetic mutation.

This phenomenon of disproportionate limbs is called Disproportionate Dwarfism or is also called chondrodysplasia.

Consequences of the study

  • Scientists now have evidence of a new way in which genome variation leads to diversity in a species.
  • Previously, scientists did not know that retrogenes can play such an influential part in bringing about diversity within a species. Now, they know the importance of retrogenes.
  • The study may also have implications in the research of a similar condition of dwarfism in humans.

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