B-chromosome evolution.
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.
Camacho
J P
JP
Departamento de Genética, Universidad de Granada, Spain. jpmcamac@ugr.es
Sharbel
T F
TF
Beukeboom
L W
LW
D000818:Animals; D005075:Biological Evolution; D002875:Chromosomes; D014644:Genetic Variation