Big dogs, small dogs - they all belong to one species of the animal kingdom: Canis lupus familiaris. How come there are dogs that are barely the size of human heads, and there are dogs that are as big as an adolescent human? The answer lies in a study made by the National Human Genome Research Institute (NHGRI).

Those NHGRI folks saw that the differences in dog size depends on the versions of the gene that encodes for insulin-like growth factor 1 (IGF1). Insulin-what? Sounds like a crazy experiment, but IGF1 is just a substance that determines size among animals. The team found out that single nucleotide polymorphisms, or variations in the DNA, located near IGF1 correlates with body size.

Testing a number of dogs great and small, the scientists discovered that IGF1 polymorphisms are a common factor in determining size. They found out that small dogs are much likely to contain two different versions of IGF1 compared to large dogs. In the studies conducted to mice and humans, and here, in dogs, the findings are similar: creatures with less IGF1 are more likely of normal size.

Now how would this affect you? Scientists would like to use this finding to probably control the body sizes of dog species. Anyone want a gigantic chihuahua? Or a miniscule Saint Bernard? The differences in sizes all lie in the presence of IGF1 in dog genes. Now if only they could find out the other genetic markers that determine dog cuteness, or attitude ... imagine being able to customize your dog.