The selfish B chromosome of rye evolved as a mosaic of multiple A chromosome and organelle derived sequences

We used chromosome sorting and second generation sequencing to analyse the sequence composition of A and B chromosomes of rye (Secale cereale). Supernumerary B chromosomes are dispensable, and not required for the normal growth and development of organisms, yet they are found in all eukaryotic phyla and are assumed to represent a specific type of selfish DNA. Little is known about their origin and molecular make-up. We propose the first comprehensive model of B chromosome evolution based on comparative sequence analysis of the A and B chromosomes of rye. Our analysis provides a new look at an enigmatic phenomenon of genome evolution in numerous species, and for the first time explains a route to B chromosome evolution.