CHROMOSOMES: PACKAGING THE DNA

Chromosomes were observed with microscopes long before anyone knew what they were made of. Now we know that chromosomes in eukaryotes

The DNA match was made possible because Arizona now has a database that contains a DNA profile of every prison inmate. In fact, every state in America now has such a database; and a national system, the National DNA Index System (NDIS), was started in 1998. By 2002, the one-millionth DNA profile had been entered into the computerized system. DNA evidence collected from any crime scene can now be quickly compared to that of any one of the million convicted offenders in the NDIS database. The system is quickly growing and the technology of DNA testing is rapidly improving. For example, a portable DNA testing kit is under development in Britain. It will be smaller than a suitcase and will be linked to the national DNA database of that country. It is expected that the crime scene evidence will be put in a solution and then placed inside the mobile unit. Silicon chip technology in the testing kit will then extract a DNA profile that will be sent to the national database via a laptop computer. The results may be returned in under an hour to the detective’s palm-held computer. Saliva on discarded cigarette butts at crime scenes has already been used successfully to provide DNA profiles of suspects. It is hoped that someday, thanks to this kind of technology, there will be no more wrongful convictions such as that of Mr. Krone, and more positive identifications of those who do deserve the jail time.

are made of proteins and DNA. Chromosomes are packages of DNA that seem to be held together by proteins. Why do organisms need packages of DNA?

Consider that DNA molecules are very, very long. A typical cell in the human body is much smaller than the period at the end of this sentence, and yet that single cell contains more than 2 meters of DNA. In addition, for DNA to do its job correctly, it cannot get tangled like a long piece of string thrown carelessly into a drawer. Chromosomes help maintain the DNA in the proper shape, untangled and ready for use. In a chromosome, the long double-helix DNA molecules get wound around protein molecules to form bundles. These bundles get looped together, and the loops, in turn, get coiled and folded together. This all works well to squeeze DNA into a very tight space and yet keep it well organized in order to do its job.