Phaseolus polytene chromosomes

Ribosomal RNA genes (rDNA)

Ribosomal 18S-25S RNA Genes

Localization

The hybridization signals of the probe for the 18S-25S RNA genes were always located at the terminal position of the nucleolus-organizing regions (NOR) of the short arms of chromosome A and K and the long arm of chromosome I. The loci of the 18S-25S rDNA are situated in the segments Ap2, Iq3 und Kp2

Hybridization signals of FISH with 18S-25S rDNA probe on 3 Phaseolus polytene chromosomes
Figure: Loci of the 18S-25S rDNA (yellow-green) on chromosomes A, I, and K. The scale bar represents 10 µm.
Nucleus with hybridization signals of FISH with 18S-25S rDNA probe on Phaseolus polytene chromosomes
Figure: The 3 NO-chromosomes A,I, and K with loci of the 18S-25S rDNA probe. (a) DAPI, (b) Double filter for FITC and propidium iodide. Signals of the 18S-25S rDNA probe in yellow-green

Hybridization signal and condensation of rDNA

Condenzation of chromatin and FISH signal shape of 18S-25S rDNA probe on Phaseolus polytene chromosomes
Figure: Different shape of hybridization signals of the 18S-25S rDNA (yellow-green) on two chromosomes K showing different degrees of condensation of the chromatin of the rDNA. (a) Large and distributed signal shape on decondensed chromatin . (b) Compact signal shape on condensed chromatin. The scale bar represents 10 µm. These fotos are taken from my diploma thesis (Nenno 1992).

Direct detection with FITC-dUTP

Direct detection of 18S-25S rDNA with FITC-dUTP of Phaseolus polytene chromosomes by FISH
Figure: Loci of the 18S-25S rDNA (yellow-green) using directly with FITC-labeled (FITC-dUTP) probe. The scale bar represents 10 µm. This foto are taken from my diploma thesis (Nenno 1992).

Interphase and meiosis

In order to confirm the number of 3 chromosomes with 18S-25S rDNA loci also interphase nuclei and chromosomes in meiosis studied by FISH. As expected 6 FISH signals were observed on interphase nuclei and 3 signals on chromosomes in TelophaseII (haploid chromosome number).

Interphase nucleus with hybridization signals of FISH with 18S-25S rDNA probe on Phaseolus polytene chromosomes
Figure: Interphase nucleus showing 6 FISH signals (yellow/green). DNA is counterstained with propidium iodide(red).
Meiosis with hybridization signals of FISH with 18S-25S rDNA probe on Phaseolus polytene chromosomes
Figure: Chromosomes in TelophaseII of Meiosis. (a) Chromosomes after DAPI staining. (b) Each of the four haploid chromosome sets show 3 FISH signals (yellow/green).

Genes of the ribosomal 5S RNA

The probe for 5S rDNA showed hybridization signals in the cHC of the NO-Chromosomes I and K. On Chromosome I the 5S rDNA locus is situated on the distal part of the cHC on the long arm in position Iq12. The second 5S rDNA locus was found on chromosome K at about the middle of the cHC of the long arm, the position of the weak DAPI band named Kq25. The co-localization with the 18S-25S and the 5S rDNA probe confirm that the loci of both rDNA types are found on chromosomes I and K.

Co-localization of 5S and 18S-25S rDNA on Phaseolus polytene chromosomes by FISH
Figure: Loci of the 5S (pink) und 18S-25S (green) rDNA on the chromosomes I and K. The scale bar represents 10 µm.
09/22/2018 23:33  Phaseolus polytene chromosomes by Mario Nenno. © 2008- All rights reserved.
Texts and images can be used for free for personal and educational use if the work on which is based this website
is cited properly as given under References. Any commercial use must be requested beforehand.