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Apart from resistance to infectious disease, there are few examples of adaptive molecular evolution in humans. A new study indicates that olfactory receptors are exceptions, with natural selection maintaining considerable allelic diversity in this multigene family.
The inability to construct animal models of human diseases caused by mutated mitochondrial DNA (mtDNA) has been a major obstacle to investigating pathogenetic mechanisms associated with specific mtDNA mutations. Mice carrying a large-scale deletion in mtDNA have now been produced. They display some of the key features of the human disorder, but there are surprising differences.
Pair-wise genome comparisons offer new sources of information about the patterns and processes that influence genomic designs. Replication-dependent rearrangements, as indicated by the symmetric gene organization pattern in the genomes of Chlamydia pneumoniae and Chlamydia trachomatis, may provide a missing link in the reconstruction of historical events from modern genomes.
Positional cloning of common disease genes is a central but elusive goal of human geneticists. Progress is now reported by Bell and colleagues in their study of NIDDM1, a locus implicated in type 2 diabetes. The complex nature of the reported association illustrates the challenge of implicating a specific gene and mutation in the causation of polygenic disease.
“They all talked at once, their voices insistent and contradictory and impatient, making of unreality a possibility, then a probability, then an incontrovertible fact, as people will when their desires become words.” —W. Faulkner, The Sound and the Fury, 1929