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Genetically perfect ValJds await their instructions in a scene from Gattaca. rid Wickeigren I f WILL DNA TECHNOLOGY LET PARENTS DESIGN THEIR KIDS? In the 1997 .science-ficiion inovic Gaiiaca. lead cluiructer Vincent Freeman is one of the "In-Valicls." When Freeman was a baby, a test of his DNA revealed that he would grow up to have bad eyesight and die at age 30. With such poor prospects, he was slotted into the bottom of society and given a dead-encljob. But Vincent dreams of becoming an astronaut. So he borrows the genetic identity of a "Valid," a man with desirable DNA. Shortly before Vincent's spaceflight is due for takeoff, a murder investigation threatens to expose his true genetic self. A t the Fertility Institutes in Los Angeles, a young married couple awaits an important result. The husband has donated sperm to fertilize an egg donated by his wife. The resulting embryo (fertilized egg) has been given a DNA test to determine whether it carries a certain mutation, or change in a gene, that causes a specific disease. If it doesn't have the mutation, the embryo will be transferred to the wife's womb. In fertility clinics across the country, prospective parents now routinely have their embryos genetically tested for life-threatening ailments. Hundreds of tests for genetic diseases are available—more than IO() of them can be done on embryos—and the number is growing. One test looks for the mutation that causes hemophilia. a disorder in which the blood is slow to coagulate (clot). Another test looks for the mutation that results in TaySach.s. a disease that severely damages the brain. Another lest .scans for a mutation that causes males to be infertile. Tay-Sachs and hemophilia are caused by mutations in a single gene. DNA tests cannot pinpoint every child's 10 CURRENT SCIENCE December 3, 2004 chances of devclopuig diseases that are influenced by many genes, including heart disease and cancer. However, tests for such conditions are probably not far off. Tests for personality traits, such as intelligenee or aggressiveness, may come too. "There is a huge amount of interest in risk profiling— that is, being able to say that a person has a 99 percent chance of developing, say, heart disease by age 30," as doctors do in Gattaca, says Harry Ostrer, a geneticist at New York University School of Medicine. GENETIC ID Today, the number of genetic tests that can be performed on any one embryo is limited. One reason is expense: Each test costs anywhere from $100 to several thousand dollars. Performing more than 14 genetic tests on a single embryo is also technically difficult. That could change soon. Scientists are working on techn(5logy that could instantly and cheaply read and interpret an individual's entire genetic code at once, instead of testing for each disease separately. Such technology could bring about a Gattaca-Vikc test that reveals an embryo's chances of contracting any of thousands of diseases as well as leanings toward aggression, studiousness. and other personality traits. "By 2025. we will probably have developed low-cost genetic risk profiles" Ostrer toid Current Science. BIOLOGICAL BARRIER? Where might genetic profiling lead? To a new social order, like the world ol' Gattaca'! Might the best schools, the best jobs, and the best health cure be reserved for Ihe people with the best geiielie profiles? Thai sort of genetie discrimination doesn't just h;ippen in the movies. In the early 1970s, after a test lor the blood disorder sickle-eell anemia was developed, ehildien were routinely tested for the mutation that eauses the disease. Some adults who were tested were denied jobs based on the results of the test. Might DNA profiling also lead to a form of eugenics— the improvement of a population by selective breeding— in which parents are told whieh cliildren they can hring the world? "In Gattaca. there was a coercive aspect about it," said Ostren "The geneticist said to the parents, 'We've selected these etnbryos for you." " Even if parents aren"t told what to do. they might still feel social pressure to provide their children with the best possible set of genes. "You can imagine that if a technology is available thai allows you to pick the best embryo—^you could feel like an irresponsible parent if you don't do that." said Kathy Hudson, the director of the Genetics and Public Policy Center at Johns Hopkins University. Children born without the use of such technology might be regarded as SEX S E L E C T I O N inferior. But would they grow up to be At fertility clinics, parents can choose the sex of their child if they wish to. Both lesser human beings? males and females normally carry 23 pairs of chromosomes, structures inside the cells that contain a person's DNA. The difference between males and females ties in the 23rd pair. Girls have two X chromosomes, white boys have one X chroinosome (right) and one Y chromosome (left). To identify the sex of an embryo before imptanting it into the mother, a fertility doctor stains the emhrgo's chromosomes so that any X chromosome appears one color and any Y chromosome appears another. Bg looidng at the colored chromosomes ., "^ under a microscope, the doctor can easily tetl whether the embryo is male or female. . -'1' ''.' —- • •— , NATURE VERSUS NURTURE Genes are not destiny. Genes shape many personality traits, but so does environment. In Gattaca, Vincent manages to qualify for the space program despite his "inferior" genes. His strongest trait is his willpower—something tliat, the movie implies, cannot be fathomed from genes alone. "Our behaviors are way more complex than genetics." said Hudson. The same is even true for heart disease, which diet and exercise may influence as much as genes do. Vincent keeps himself physically fit and. perhaps as a result, does not die when predicted. "My heail." he says, "is already lO.OtK) beats overdue." CS December 3, 2004 CURRENT SDENCE 11