Physical mapping and molecular structure of B chromosomes in species of the genus Characidium (Characiformes, Crenuchidae)

Author(s)

Érica Alves Serrano Freitas

• Document type: Doctoral Thesis
• Press: Botucatu. 2017-01-11.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2016-12-07
• Advisor: Fausto Foresti

Abstract

B chromosomes are apparently dispensable components found in the genomes of many species, mainly composed of repetitive DNA sequences. These elements have been reported in approximately 60 fish species, including the genus Characidium, in which these elements do not appear to have a single origin. In order to investigate the origin and molecular content of B chromosomes in Characidium, we analyzed two species bearing B chromosomes, Characidium gomesi and Characidium alipioi, using a combination of molecular cytogenetic techniques, DNA sequence analysis and massive sequencing. Our results showed that i) the B chromosomes of both species had an intraspecific origin, but from different chromosomes; ii) the two B-variants of C. gomesi share the same repetitive DNA sequences, five distributed on the elements of the A set, and on B and ZW chromosomes, and one restricted to B and ZW chromosomes, reforcing its origin from the sex chromosomes; iii) the supernumerary in C. alipioi probably arose from the chromosomes of the submetacentric pair 19; iv) B chromosomes in C. alipioi became a conducive setting for repetitive DNAs accumulation after its emergence; v) the sequence of H3 histone gene isolated from the chromosomes of the A set and B chromosomes of C. gomesi presented identical aminoacid sequences and the rates of dN/dS were lower for those from the B genome, suggesting the action of a positive selection and possible transcription of the supernumerary copies. The results reveals the importance of multiple approaches of chromosomal and molecular methods to understand issues related to evolutionary biology of supernumerary chromosomes, once allowed to increase knowledge about the structure, composition and origin of B chromosomes in representatives of the genus Characidium. These observations reinforce the proposition of this fish group as an interesting model for studies on the origin and structure of these genomic elements and the evolutionary strategies presented by supernumerary chromosomes in fish. (AU)

• FAPESP's process: 13/02143-3 - PHYSICAL MAPPING AND MOLECULAR STRUCTURE OF B CHROMOSOMES IN THE GENUS Characidium ( CHARACIFORMES, CRENUCHIDAE )
• Grantee: Érica Alves Serrano Freitas
• Support Opportunities: Scholarships in Brazil - Doctorate