Genes within Genes

Tyler Hampton in Inference Review:

In a publication titled “Russian Doll Genes and Complex Chromosome Rearrangements in Oxytricha trifallax,” Jasper Braun et al. explore what they describe as “architectures that transcend simple twists and turns of the DNA.” The paper is short, dry, clear, and interesting.

Oxytricha trifallax is a unicellular eukaryotic species and a ciliate, one widely known for beautiful, but bizarre, genetic acrobatics. Members of O. trifallax possess two nuclei within their single-cell frame. The two nuclei are analogous to the diploid somatic cells and the haploid reproductive cells found in multicellular eukaryotes. In ciliates, the physically larger nucleus is called the macronucleus; the smaller one, the micronucleus. Chromosomes in the macronucleus are accessed for ordinary biochemical affairs. DNA in the micronucleus is involved only in reproduction.

Under ordinary circumstances, O. trifallax reproduces asexually by cloning. Under conditions of stress, one cell meets another in sexual conjugation. What is odd is that, in O. trifallax, all conjugal events begin and end with exactly two individuals. Each cell exchanges 50 percent of its micronuclear DNA. Both leave transformed. After O. trifallax recombines and dissociates from its partner, it goes on increasing its numbers by cloning.

More here.