Scientists Map Two Chromosomes, Will Help Genetic Studies
NEW YORK (AP) _ Scientists have made the most complete maps yet of individual human chromosomes, another advance in an ambitious effort to figure out the body’s genetic blueprint and someday find the causes of many diseases.
The researchers mapped out the most significant portion of the Y chromosome, which makes fetuses develop as males, and of chromosome 21, which is linked to such diseases as Down syndome and some cases of Alzheimer’s.
Such maps help scientists isolate new genes for analysis, and experts said the significance of the new work goes beyond the two chromosomes studied.
The work shows that ″useful detailed maps can be generated rather quickly,″ said Mark Guyer, assistant director for program coordination at the National Center for Human Genome Research, part of the National Institutes of Health.
Chromosomes are microscopic, rod-shaped structures that contain long strings of deoxyribonucleic acid, or DNA. Parts of this DNA make up genes.
An international research effort called the Human Genome Project is trying to map all the human chromosomes and eventually reveal the details of all genes.
The chromosome 21 map is reported in today’s issue of the journal Nature by Daniel Cohen of the Center for the Study of Human Polymorphisms in Paris and of Genethon in Evry, France, with 35 co-authors from France, Japan, Spain and the United States.
The Y chromosome map will be reported in Friday’s issue of the journal Science by David Page, Simon Foote, Douglas Vollrath and Adrienne Hilton of the Whitehead Institute for Biomedical Research and the Massachusetts Institute of Technology in Cambridge.
The researchers combined overlapping fragments of genetic material to create the maps. The maps contain landmarks that scientists hope to use to identify individual genes and zero in on those responsible for certain diseases.
″These maps are both more complete than anything we’ve had before,″ said Charles Cantor, director of the Center for Advanced Research in Biotechnology at Boston University.
He called them an important step in the effort to discover details of the 100,000 or more human genes, but he emphasized that the maps covered only a small fraction of the genetic material people have.
The two chromosomes are among the smallest human ones. Everybody has 22 types, plus the X chromosome in women and the X and the Y chromosomes in men.
The Y chromosome map was constructed by analyzing DNA from a man who had four Y chromosomes instead of one. The extra chromosomes provided more material for analysis.
Researchers chopped the samples of Y chromosome into fragments. Then they looked to see if each fragment contained any of 160 shorter bits of DNA.
If two fragments shared one of these bits, they had to represent overlapping regions of the Y chromosome. These overlaps and other analysis were used essentially to combine 196 fragments into a single span, which the researchers said covered nearly all of the chromosome region they wanted to map.
The process revealed 127 landmarks along the span.
The chromosome 21 map was made from 810 overlapping DNA fragments.