Scientists at Harvard and MIT’s Broad Institute have mapped the genes of man’s  best friend, the dog, in the hopes of uncovering insights into diseases that affect both humans and canines.

The results, published in the December 8 issue of the science journal Nature, include the first comparative analysis of three mammalian genomes—human, mouse, and dog.

Tarjei S. Mikkelsen, a graduate student at the Harvard-MIT Division of Health Sciences and Technology (HST) and one of the leaders of the research project, said that researchers were surprised that the sequences that humans had in common with dogs were the same sequences that humans shared with mice.  

The similarities between the three mammalian species allow researchers to identify the most biologically important genetic elements in humans, Mikkelsen said.

“This is a significant step toward assembling a complete parts list for the human genome,” he added.

Mikkelsen and fellow researchers have found that the majority of the DNA common to all three mammals was significant for their growth and development.

Kerstin Lindblad-Toh, the first author of the Nature paper and co-director of the Genome Sequencing and Analysis program at the Broad, said that because the DNA sequences, or haplotypes, are much longer in dogs than in humans, a canine genetic map can be used instead of the human genome to identify the haplotypes responsible for certain human diseases.

According to Karlsson, researchers must examine at least 300,000 single nucleotide polymorphisms (SNPs) in thousands of patients to find the genes that cause disease in humans. “Because of their unique genomic organization, we need about 30 times fewer SNPs and only a few hundred volunteers to accomplish this task in dogs,” Karlsson said in a statement from the institute.

According to the new research, dogs have about 19,300 genes. Human beings have about 22,000 genes.

Broad Institute researchers are currently working to map an increasing number of mammal genomes, according to Lindblad-Toh.

“We are sequencing eight, soon will be sixteen, different mammals at lower coverage, including the opossum,” she said.

The Broad Institute, a joint venture of Harvard and MIT founded in 2003, received an additional $100 million in funding from philanthropists Eli and Edythe L. Broad earlier this month.