Analysis of the genome continued to dominate this week's news as well. A principal puzzle is that of how human complexity is built in view of the finding that people don't seem to have that many more genes than do the two little invertebrates that have been sequenced so far, the fruitfly and the roundworm. Biologists have several ideas as to how nature might perform this trick.
Human genes seem to produce more alternative proteins than fly or worm genes.
Animal genes are not continuous stretches of DNA but are made up of separate segments, called exons. After being copied from the DNA these exons are brought together and the intervening pieces of DNA are snipped out. However, the cell has ways of skipping various exons so as to make several variant forms of a protein from a single gene. Besides coming in alternative spice forms, human proteins are also more complex because they possess more functional units or domains than do invertebrate proteins. Another explanation of human complexity, held so far by a single critic but a substantial one, is that the two rival teams have seriously undercounted the number of human genes.