The battle of the sexes has taken on a new meaning with the remarkable discoveries coming from studies of the human genome. The X (female) and Y (male) chromosomes are constantly at war and the genetic details provided by the genome have given us an unprecedented view of the action.
This struggle for genetic advantage is just one small piece of the DNA puzzle emerging from the ongoing analysis of the human genome. Today's linked announcements in Washington, Tokyo, Berlin, London and Paris by the publicly-funded Human Genome Project and the private firm, Celera Genomics, include dozens of new findings that are both startling and thought-provoking.
Researchers, for example, were surprised at the comparatively low number of genes our genome contains. Scientists had long assumed there were at least 100,000 genes and possibly 140,000. In fact the genome research has found we have only between 30,000 and 40,000 genes.
This is only twice as many as a worm or a fly despite our apparent much greater complexity. Celera's president, Dr Craig Venter, interpreted this as meaning that the environment played a much greater role than expected in a person's development. There were too few genes for complex behaviour to be controlled by genes, he said.
The countering HGP interpretation of this, however, is that each gene is capable of producing a wide range of proteins, not just one, and this in turn provides for a rich and varied output from each gene. The question remains, however, whether this variety is controlled more by environment or by the actions of genes working on one another.
Evidence has also emerged that we carry 223 genes which are more akin to bacterial genes than any other form of genetic material yet studied. The current assumption is that infective bacteria some time in the past managed to incorporate bacterial DNA into human DNA, building for itself a permanent new home for its genes.
Researchers have found that at least some of these genes and the proteins they produce have become an essential part of our own physical make-up. One is crucial for normal brain function, but appears to have come from bacterial DNA rather than mutation of an existing human gene.
A new view has also been provided on the fight between the X and Y chromosomes. The struggle began long ago when sexual differentiation, physical differences between male and female, began to emerge. Males picked up a gene or genes which gave them a physical advantage but the X chromosome is far more "genetically" fit than Y, according to researchers.
Physically, the Y chromosome has been reduced to a mere "stump" and can no longer recombine or mix its genetic contents, according to the researchers. Many of its genes have ceased to function and those that do provide Y with a competitive advantage against the X. These genes are associated with testes development and sperm production and survive only on Y, but many are repeated over and over, as if to ensure that they survive as the evolutionary battle continues.
A number of the research teams undertook "data mining", computational analysis of the genome to dig out specific types of information. Dr David Valle and colleagues writing in Nature studied nearly 1,000 disease-causing genes. They found that more than 30 per cent of inherited diseases caused by a single gene defect are related to mutated enzymes. They also uncovered an age-related dimension to these mutations. Dr Michael Stratton and colleagues also writing in Nature found that cancer isn't typically caused by a single mutation. Rather it involves large-scale "meltdown" of the genome, with numerous serious DNA mistakes. They also discovered that genes related to cancer can be identified by comparing damaged DNA and normal DNA.
Previously unknown genes associated with our daily biological rhythm were uncovered by Dr Steve Reppert and colleagues. Clock genes drive our sleep-wake cycle and cause the symptoms of jet lag at the end of a long flight. A better understanding of these genes could help overcome sleep disorders.
In another central research paper in Nature, Dr David Altshuler and colleagues map 1.42 million individual variations in the genome. These single-point variations will help identify diseases but also map the variations between populations, important in the study of human evolution and migration.