title: B chromosome ancestry revealed by histone genes in the migratory locust.
abstract: In addition to the standard set of chromosomes (A), about 15% of eukaryote genomes carry B chromosomes. In most cases, B chromosomes behave as genomic parasites being detrimental for the individuals carrying them and prospering in natural populations because of transmission advantages (drive). B chromosomes are mostly made up of repetitive DNA sequences, especially ribosomal DNA (rDNA), satellite DNA and mobile elements. In only two cases have B chromosomes been shown to carry protein-coding genes. Although some B chromosomes seem to have derived from interspecific hybridisation, the most likely source of B chromosomes is the host genome itself, but the specific A chromosome being the B ancestor has not been identified in any B-containing species. Here, we provide strong evidence for B chromosome ancestry in the migratory locust, based on the location of genes for the H3 and H4 histones in the B chromosome and a single A chromosome pair (i.e. the eighth in order of decreasing size). The high DNA sequence similarity of A and B chromosome H3-H4 genes supports B-origin from chromosome 8. The higher variation shown by B sequences, compared to A sequences, suggests that B chromosome sequences are most likely inactive and thus less subjected to purifying selection. Estimates of time of divergence for histone genes from A and B chromosomes suggest that B chromosomes are quite old (>750,000 years), showing the B-chromosome ability to persist in natural populations for long periods of time.
authors.affiliation: Departamento de Genética, Universidad de Granada, 18071, Granada, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Teruel
authors.forename: Josefa
authors.initials: J
authors.lastname: Cabrero
authors.forename: Francisco
authors.initials: F
authors.lastname: Perfectti
authors.forename: Juan Pedro M
authors.initials: JP
authors.lastname: Camacho
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000235:genetics*; D003001:Cloning, Molecular; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D017344:Genes, Insect; D006657:Histones / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D048188:Locusta migratoria / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013997:Time Factors
chemical_list: D004275:DNA, Ribosomal; D006657:Histones