WASHINGTON – Scientists say they have largely deciphered the genetic code of the mouse, a step that will provide a vantage point to better understand the biology and diseases of people.

Celera Genomics of Rockville, Md., said Monday its data covered more than 99 percent of the roughly 3 billion “letters” in the mouse code, called its genome.

That’s about the same genome size as people have. While Celera has largely determined the order of the letters, it hasn’t yet counted up the genes or defined other features, Celera vice president Mark Adams said in an interview.

Ken Paigen, director of The Jackson Laboratory in Bar Harbor, Maine, a major center for studies of mouse genetics, said, “If it’s true, it’s wonderful.”

Scientists have several reasons to want the sequence of the mouse genome in hand. One is to help them use mice in lab experiments to find out about human disease.

“The mouse is the principal means we have for discovering the genes that underlie diseases and understanding what they do,” Paigen said. “Having the sequence will greatly improve that.”

The mouse code also can help scientists understand the human genome, he said.

“Comparison between the two helps to separate out the parts that are functionally important from the parts that are less so,” Paigen said.

Eric Lander of the Whitehead Institute Center for Genomic Research in Cambridge, Mass., said such comparisons should help scientists find DNA regions that regulate the activity of genes, and figure out the control circuits. It probably will take comparisons across the genomes of three to five species to do that, he said.

Adams said the mouse genome also should help scientists understand differences in how diseases behave in mice and people. That might provide insights that lead to treatments targeting the spread of cancer, for example, he said.

Celera will make its mouse genome data available to its customers, Adams said.