Wondergenes: Genetic Enhancement and the Future of Society

3 Four Revolutions

18 Wondergenes Four Revolutions 3 The unraveling of the mystery of the genome has led to a number of developments with profound implications for society. To understand the prospects for genetic enhancement, it is first necessary to understand these developments. THE REVOLUTION IN FORENSIC GENETICS One of the first applications of new genetic knowledge to have a major impact on society was the use of DNA to identify people. This has given rise to the new field of forensic genetics. While this is the most mature and well-accepted societal use of genetic knowledge , many aspects remain controversial. As noted in Chapter 2, the precise sequence of nucleotides in human DNA varies slightly from one individual to another. Some of these variations occur in the genes, the stretches of DNA that code for proteins, and sometimes this causes or makes people susceptible to diseases, like Huntington disease or breast cancer. Nucleotide differences also occur in the DNA regions that do not code for proteins, and therefore do not directly affect a person’s health 19 Four Revolutions or the way the person looks or behaves. In some of these segments of non-coding DNA, nucleotide differences—such as different numbers of repeating nucleotides—occur fairly frequently, so that if you took DNA from a number of individuals and sequenced the DNA in these segments, you would be likely to find small differences between the individuals. Consequently, if you took two samples of DNA, compared the sequences in a number of these DNA segments and found that both samples had the same sequences , the chances would be high that they came from the same person. This is the basis for modern forensic genetics. Forensic genetics first compared individuals on the basis of blood types and serum proteins, which follow family patterns of inheritance , rather than on the basis of DNA sequences.These techniques were occasionally used in criminal cases, but more often they were used in civil cases like paternity disputes, where the standard of evidence is less stringent. Then, in 1985, Alec Jeffreys and colleagues in Britain used a comparison of DNA segments to exonerate one suspect in two rape-murder cases and to convict another.1 In 1987, DNA evidence was used for the first time in the United States to obtain a conviction in a rape case in Florida.2 Judges struggled to understand the new evidence and to decide if it was admissible and how much weight it should be given. Gradually, they came to accept its value in identifying suspects, in helping to establish guilt, and in exculpating the innocent. The DNA used in forensic genetics can come from a variety of sources: blood, semen, hair, saliva, even cells scraped from the skin or from the inside of the cheek. DNA found on a crime victim or at a crime scene can be compared to DNA from a suspect to see if they match. An important technical breakthrough was polymerase chain reaction, which allows minute amounts of DNA to be copied many times, or “amplified,” so that small samples of DNA can be analyzed and compared. A current technique uses “short tandem repeats” (STRs) that comprise only three to five nucleotide base pairs; the FBI has identified thirteen STRs at different places on the human genome as the standard battery for identification tests. In early DNA testing, a smaller number of DNA segments were compared. As a result, the probability that two matching samples 20 Wondergenes came from different people was fairly high. In New York v. Castro, a murder case in 1989, for example, the testing laboratory reported that the probability was on the order of one in a million that the DNA from a watch found at the crime scene came from someone other than the suspect.3 At first this may seem like overwhelming evidence. But there might be as many as 250 Americans whose DNA could have been deposited on the watch, and who therefore could also have committed the crime. For the evidence to be convincing beyond a reasonable doubt, which is the standard for a criminal conviction, there would have to be additional evidence linking the suspect to the crime, like living or being seen near the scene, or a motive. Judges had to be on guard for what was known as the “prosecutor’s fallacy”—attempting to establish guilt on the basis of what...