Intraindividual and Interspecies Variation in the 5S rDNA of Coregonid Fish |
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Authors: | S Linn Sajdak Kent M Reed Ruth B Phillips |
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Institution: | (1) Department of Biological Sciences, University of Wisconsin—Milwaukee, Milwaukee, WI 53201, USA, US |
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Abstract: | This study was designed to characterize further the nontranscribed intergenic spacers (NTSs) of the 5S rRNA genes of fish
and evaluate this marker as a tool for comparative studies. Two members of the closely related North American Great Lakes
cisco species complex (Coregonus artedi and C. zenithicus) were chosen for comparison. Fluorescence in situ hybridization found the ciscoes to have a single multicopy 5S locus located
in a C band-positive region of the largest submetacentric chromosome. The entire NTS was amplified from the two species by
polymerase chain reaction with oligonucleotide primers anchored in the conserved 5S coding region. Complete sequences were
determined for 25 clones from four individuals representing two discrete NTS length variants. Sequence analysis found the
length variants to result from presence of a 130-bp direct repeat. No two sequences from a single fish were identical. Examination
of sequence from the coding region revealed two types of 5S genes in addition to pseudogenes. This suggests the presence of
both somatic and germline (oocyte) forms of the 5S gene in the genome of Coregonus. The amount of variation present among NTS sequences indicates that accumulation of variation (mutation) is greater in this
multicopy gene than is gene conversion (homogenization). The high level of sequence variation makes the 5S NTS an inappropriate
DNA sequence for comparisons of closely related taxa.
Received: 22 August 1997 / Accepted: 31 October 1997 |
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Keywords: | :Coregonus— 5S ribosomal DNA — Nontranscribed spacer region |
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