A New Variant B Chromosome in Auchenipteridae: The Role of (GATA) < sub > n < /sub > and (TTAGGG) < sub > n < /sub > Sequences in Understanding the Evolution of Supernumeraries in < b > < i > Trachelyopterus < /i > < /b >

This study aimed to describe and understand the structure and evolution ofTrachelyopterus B chromosomes, mainly through physical mapping of repetitive elements. A diploid number of 58 chromosomes was found for all individuals, as well as the presence of B chromosomes. ForT. porosus this is the first report of a supernumerary. The sympatric species ofT. galeatus andT. porosus from Amazon River had 1 –3 B chromosomes andT. galeatus from Paraguay River had 1 –2 B chromosomes, all of them showed intra- and interindividual numerical variation. Two females ofT. porosus exhibited a new variant B chromosome (B2), previously not seen in Auchenipteridae, which might have originated from B1 chromosomes. All B chromosomes were entirely heterochromatic. In contrast to all complement A and B2 chromosomes, in which the telomeric sequences were found in the telomeric regions, B1 chromosomes of all populations were totally marked by (TTAGGG)n probes. (GATA)n sequence sites were found through all complement A chromosomes, but B1 and B2 chromosomes exhibited only a clustered block in one of the chromosome arms. The most frequent B chromosomes (B1) in all populations/species, including those previously studied in Auchenipteridae catfishes, share the following characteristics: totally heterochromatic, small, metacentric, with accumulation of repetitive (TTAGGG)n sequences, and a low number of (GATA)n copies, which might suggest a common ancient origin inTrachelyopterus species/populations.Cyt...
Source: Cytogenetic and Genome Research - Category: Genetics & Stem Cells Source Type: research