Genetic Rearrangement: One genome’s junk is another’s garbage
Figures

Junk DNA in Tetrahymena.
Left: Tetrahymena is a single-celled ciliate that stores its germline genome in a micronucleus and its somatic genome in a macronucleus. During reproduction, two micronuclei fuse to form a zygotic nucleus that splits to form a new germline micronucleus and a new somatic macronucleus. This means that the genetic material in the somatic macronuclei of the parents is discarded. Right: Germline DNA (purple; top) remains intact in the germline micronucleus, but is processed in the somatic macronucleus to form somatic DNA (blue; bottom). Junk DNA in the form of internally eliminated sequences (IES; green boxes) is removed and the DNA fragments at chromosome breakage sites (Cbs; red arrowhead) to form five chromosomes, which are stabilized by the addition of telomeres (purple triangles) at their ends.