Human Heredity 9th Edition by Michael Cummings

Exercise 1

Can DNA profiling identify the source of a sample with absolute certainty? Because any two human genomes differ at about 3 million sites, no two persons (except identical twins) have the same DNA sequence. Unique identification with DNA profiling is there-fore possible if enough sites of variation are examined. However, the systems used today examine only a few sites of variation and have only limited resolution for measuring the variability at each site. There is a chance that two persons might have DNA patterns (i.e., genetic types) that match at the small number of sites examined. Nonetheless, even with today's technology, which uses three to five loci, a match between two DNA patterns can be considered strong evidence that the two samples came from the same source. How is DNA profiling currently being used?
¦ Paternity and maternity testing: Because a person inherits his or her STRs from his or her parents, STR patterns can be used to establish paternity and maternity. The patterns are so specific that a parental STR pattern can be reconstructed even if only the children's STR patterns are known (the more children produced, the more reliable the reconstruction). Parent-child STR pattern analysis has been used to solve standard father-identification cases and more complicated cases confirming nationality and, in instances of adoption, biological parenthood.
¦ Criminal identification and forensics: DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared, through STR patterns, with the DNA of a criminal suspect to determine guilt or innocence. STR patterns are also useful in establishing the identity of a homicide victim. However, DNA profiles have limitations. In cases where one identical twin has committed a crime, DNA evidence may not be helpful.
¦ Personal identification: The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals has been discussed, but this is not likely to happen any time in the foreseeable future. The technology required to isolate, keep on file, and analyze millions of very specific STR patterns is both expensive and impractical. Social security numbers, picture IDs, and other more mundane methods are much more likely to remain ways of establishing personal identification. However, the FBI and other police agencies and the military are enthusiastic proponents of DNA data banks. The practice has civil-liberties implications because police can go on "fishing expeditions" with DNA readouts.
A police chief in a large U.S. city has proposed that everyone who is arrested be DNA fingerprinted; this information would be stored in a national database even if those arrested are later found to be innocent. The chief is actively seeking funding from his state legislature to begin such a program. Do you support such a program? Why or why not? Could there be abuses of the program?