The pachytene chromosomes of maize as revealed by fluorescence in situ hybridization with repetitive DNA sequences |
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Authors: | C C Chen C M Chen F C Hsu C J Wang J T Yang Y Y Kao |
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Institution: | (1) Department of Botany, National Taiwan University, Taipei, Taiwan, Republic of China e-mail: chencc@ccms.ntu.edu.tw Fax: +886-2-2391-8940, TW;(2) Institute of Botany, Academia Sinica, Taipei, Taiwan, Republic of China, TW |
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Abstract: | A repetitive DNA sequence, ZmCR2.6c, was isolated from maize based on centromeric sequence CCS1 of the wild grass Brachypodium sylvaticum. ZmCR2.6c is 309 bp in length and shares 65% homology to bases 421–721 of the sorghum centromeric sequence pSau3A9. Fluorescence
in situ hybridization (FISH) localized ZmCR2.6c to the primary constrictions of pachytene bivalents and to the stretched regions
of MI/AI chromosomes, indicating that ZmCR2.6c is an important part of the centromere. Based on measurements of chromosome
lengths and the positions of FISH signals of several cells, a pachytene karyotype was constructed for maize inbred line KYS.
The karyotype agrees well with those derived from traditional analyses. Four classes of tandemly repeated sequences were mapped
to the karyotype by FISH. Repeats 180 bp long are present in cytologically detectable knobs on 5L, 6S, 6L, 7L, and 9S, as
well as at the termini and in the interstitial regions of many chromosomes not reported previously. A most interesting finding
is the presence of 180-bp repeats in the NOR-secondary constriction. TR-1 elements co-exist with 180-bp repeats in the knob
on 6S and form alone a small cluster in 4L. 26S and 5S rRNA genes are located in the NOR and at 2L.88, respectively. The combination
of chromosome length, centromere position, and distribution of the tandem repeats allows all chromosomes to be identified
unambiguously. The results presented form an important basis for using FISH for physical mapping and for investigating genome
organization in maize.
Received: 29 June 1999 / Accepted: 10 November 1999 |
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Keywords: | Zea mays Pachytene chromosome Karyotype Repetitive DNA sequence Fluorescence in situ hybridization |
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