B-chromosome evolution

Philos Trans R Soc Lond B Biol Sci. 2000 Feb 29;355(1394):163-78. doi: 10.1098/rstb.2000.0556.


B chromosomes are extra chromosomes to the standard complement that occur in many organisms. They can originate in a number of ways including derivation from autosomes and sex chromosomes in intra- and interspecies crosses. Their subsequent molecular evolution resembles that of univalent sex chromosomes, which involves gene silencing, heterochromatinization and the accumulation of repetitive DNA and transposons. B-chromosome frequencies in populations result from a balance between their transmission rates and their effects on host fitness. Their long-term evolution is considered to be the outcome of selection on the host genome to eliminate B chromosomes or suppress their effects and on the B chromosome's ability to escape through the generation of new variants. Because B chromosomes interact with the standard chromosomes, they can play an important role in genome evolution and may be useful for studying molecular evolutionary processes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Biological Evolution*
  • Chromosomes*
  • Genetic Variation*