When 18-month-old Luke Do was diagnosed with leukemia and needed a bone marrow transplant, doctors told his parents that his chances of finding a matching genetic donor were "slim to none."
"I had no idea it was so difficult for multiracials," said Luke's mother, Sarah Gaskins of San Jose, who is Japanese and Irish, while Luke's father Lam Do is Vietnamese.
Gaskins thinks the census should have a specific "multiracial" category. It would increase the profile of a group with distinct needs, and would encourage people to acknowledge their full racial heritage, she said.
In 2000, when the federal government started allowing people to choose all applicable racial categories on the census, many predicted an explosion in the number of people who would identify as multiracial. Some called it the beginning of the end of single-race classification.
It hasn't happened.
Despite the rapid growth in mixed marriages and relationships producing more children like Luke Do, the number of people checking off more than one race on census surveys has dropped this decade, prompting some to say the nation's racial statistics are not capturing the full measure of its evolving diversity.
That criticism was highlighted this week, when the U.S. Census Bureau released new population projections that predict that as far into the future as 2050, just 3.7 percent of the U.S. population would categorize themselves as being members of more than one race.
Despite the prominence of multiracial figures like Barack Obama and Tiger Woods, some demographers say that many people's views about race continue to be shaped by old beliefs.
About 2.4 percent of the U.S. population checked more than one racial category on their 2000 census forms. But University of Michigan demographer Reynolds Farley's analysis found that by 2005, that share had gone down to 1.9 percent.
"I think most people in the United States assume that individuals are in one, and one only, racial group," Farley said.
The state of California is more racially diverse than the nation. But projections by the California Department of Finance say multiracial people will be just 2.4 percent of the state's population in 2050.
The multiracial issue encompasses the difference between two of the best-known such individuals in the world – Woods and Obama.
In 1997, Woods caused a firestorm when he said he did not want to be pidgeonholed in a single racial box – black. The former Stanford University student, whose late father was black and whose mother is Thai, famously described how he made up the word "Cablinasian" to incorporate his full heritage of Caucasian, Black, American Indian and Asian.
Obama talks extensively about being the son of a black father from Kenya and a white mother from Kansas, but consistently describes himself as African-American.
The government's racial and ethnic statistics are a combination of how people define themselves within contemporary society, and the choices government offers to record those perceptions.
Obama was born before a crucial event in America's racial history, the Supreme Court's 1967 Loving vs. Virginia decision, which struck down state laws that banned interracial marriage.
"He's pre-Loving," said James Landrith, a 37-year-old blogger and founder of The Multiracial Activist. "It's the younger generation that is becoming more aware that these lines don't make sense. They don't want to be put in a box and told, 'You have to conform to this identity; you have to embrace this identity, or you're a race traitor.' "
Different racial groups see a different Obama. A 2006 Zogby poll found that while 66 percent of African-Americans see Obama as black, a majority of whites and Hispanics see him as biracial. The Obama campaign would not say how he answered his 2000 census form.
How Obama labels himself racially makes little political difference, said John Kenneth White, a political scientist at the Catholic University of America.
"I don't think this is something he can simply say through words if he says, 'I'm biracial,' or 'I'm half-white,' " White said. "I think what he will do is tell his story again at the convention, in a way that says this is not a story about race; this is a story about America."
Obama may change how others perceive themselves.
"The visibility of Barack Obama may lead more people to identify with multiple races," Farley said.
The history of the U.S. census is littered with anachronistic terms like "mulatto" and "quadroon" that were once official government categories for multiracial people.
The first census in 1790 broke race into "free whites" and "slaves." By 1930, the census defined "Mexican" as a race. Today, Mexicans are part of the "Hispanic or Latino" ethnicity, a government-created label that includes people whose descent is from Spanish-speaking countries of Latin America, the Caribbean and Europe. They can be of any race.
While the census allows people to check as many racial or ethnic categories that apply, there is no "multiracial" box. There are no plans to include one for the 2010 census.
'Our own slice'
A "multiracial" category would bolster consciousness of the group, said Susan Graham, executive director of Los Banos-based Project Race, a national multiracial group.
"We want our own slice of that pie chart," Graham said.
Groups like the Alameda-based Asian American Donors Program say a multiracial category could raise the group's profile. Luke Do, his mother said, was "extremely, extremely fortunate" to find a Seattle policeman six years ago who was a suitable marrow donor. The boy is alive and well today.
"The difficult thing about the multiracial community is that there is no community," said Asia Blume, recruitment director for the program. "They exist, but there's not many organizations dedicated to them."