This week's nature features two articles elucidating questions that have persistently puzzled scientists!
The first involves the mystery of why so much genetic variation tends to underlie traits believed to be under strong sexual selection:
Researchers identified a single locus, RXFP2, with two alleles that, in Soay sheep, explains most of the genetic variation in horn morphology, a trait important in intrasexual competition. Ho+ (large horn) homozygotes enjoy greater average annual reproductive success, but Hop (horns range from small to underdeveloped) homozygotes live longer. Heterozygotes turn out to have the highest lifetime reproductive success, demonstrating an apparent life history compromise between reproductive success and longevity. This heterozygote advantage explains the maintenance of horn variation in this species.
The second article sheds light on the mystery of the abundance of ncRNA, dubbed the "dark matter" of the genome.
The authors of this study scanned human chromosomes for promotor transcription initiation complexes. They identified ~160,000 complexes, about a quarter of which corresponded to coding genes. The remaining 150,000 or so were located in noncoding regions, suggesting that the transcription of ncRNAs functions similarly to transcription of coding regions, rather than being randomly-generated biological noise, as some have suggested. Interestingly, ~50% of complexes were in heterochromatic regions, or regions of high chromatin density, which are thought to be impoverished for transcription. Another notable finding was that many regions that have been characterized as lacking a TATA box, do retain degenerated TATA sequences, with quality of the sequence correlated with presence of transcription factors.