Extensive Direct-Tandem Organization of a Long Repeat DNA Sequence on the Y Chromosome of Chinook Salmon (Oncorhynchus tshawytscha) |
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Authors: | Robert H Devlin Geoff W Stone Duane E Smailus |
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Institution: | (1) Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, B.C., Canada V7V 1N6, CA |
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Abstract: | A long repetitive DNA sequence (OtY8) has been cloned from male chinook salmon and its genomic organization has been characterized.
The repeat has a unit length of 8 kb and is present approximately 300 times per diploid male nucleus. All internal fragments
within the 8-kb repeat segregate from father to son, suggesting that the entire repeat unit is located on the Y chromosome.
The organization of this sequence into an 8-kb repeat unit is restricted to the Y chromosome, as are several male-specific
repeat subtypes identified on the basis of restriction-site variation. The repeat possesses only weak internal sequence similarities,
suggesting that OtY8 has not arisen by duplication of a smaller repeat unit, as is the case for other long tandem arrays found
in eukaryotes. Based on a laddered pattern arising from partial digestion of genomic DNA with a restriction enzyme which cuts
only once per repeat unit, this sequence is not dispersed on the Y chromosome but is organized as a head-to-tail tandem array.
Pulse-gel electrophoresis reveals that the direct-tandem repeats are organized into at least six separate clusters containing
approximately 12 to 250 copies, comprising some 2.4 Mb of Y-chromosomal DNA in total. Related sequences with nucleotide substitutions
and DNA insertions relative to the Y-chromosomal fragment are found elsewhere in the genome but at much lower copy number
and, although similar sequences are also found in other salmonid species, the amplification of the repeat into a Y-chromosome-linked
tandem array is only observed in chinook salmon. The OtY8 repetitive sequence is genetically tightly associated with the sex-determination
locus and provides an opportunity to examine the evolution of the Y chromosome and sex determination process in a lower vertebrate.
Received: 4 April 1997 / Accepted: 22 July 1997 |
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Keywords: | : Tandem-Repeat DNA — Salmon — Y chromosome |
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