Skip to main content
Genetics logoLink to Genetics
. 1986 Aug;113(4):1037–1056. doi: 10.1093/genetics/113.4.1037

Investigation of Homologous Crossing over and Sister Chromatid Exchange in the Wheat Nor-B2 Locus Coding for Rrna and Gli-B2 Locus Coding for Gliadins

J Dvořák 1,2, R Appels 1,2
PMCID: PMC1202910  PMID: 17246339

Abstract

Recombination was investigated within the Nor-B2 locus of wheat chromosome 6B that contains several thousand of the 18S-5.8S-26S rRNA (rDNA) repeated units. Additionally, recombination was assessed for several chromosome regions, in arm 6Bq between the centromere and the B2 locus (awn suppressor) and in arm 6Bp between the centromere and Nor-B2, between Nor-B2 and a distal C-band and between Nor-B2 and Gli-B2 coding for gliadins. The experimental design permitted the distinction between crossing over between homologous chromosomes and exchange between sister chromatids. No homologous crossing over within the Nor-B2 locus was found in a sample of 446 chromosomes, but one exchange with the attributes of unequal sister chromatid exchange was identified. The molecular characteristics of this presumed sister chromatid exchange indicate that the spacer variants present in the Nor-B2 locus are clustered. No homologous recombination was detected within the distal Gli-B2 locus containing repeated genes coding for gliadin seed-storage proteins. Both arms of chromosome 6B showed low crossing-over frequency in the proximal regions. The distance from the centromere to Nor-B2 was only from 0.3 to 2.2 cM although it accounts for about two-thirds of the metaphase chromosome arm, which shows a great distortion of the metaphase map of the arm. The level of homologous recombination within the Nor-B2 locus is lower than in the chromosome region immediately distal to it. Whether it is comparable to that in the chromosome region proximal to it could not be determined. Recombination frequencies of different pairs of chromosome 6B in all but one interval paralleled the frequencies of their metaphase I pairing: Lower pairing at metaphase I was paralleled by lower crossing-over frequency. This relationship indicated that reduced metaphase I pairing between 6B chromosomes from different populations is due to impaired crossing-over and not due to precocious chiasma terminalization.

Full Text

The Full Text of this article is available as a PDF (2.3 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Bennett M. D. Nuclear DNA content and minimum generation time in herbaceous plants. Proc R Soc Lond B Biol Sci. 1972 Jun 6;181(1063):109–135. doi: 10.1098/rspb.1972.0042. [DOI] [PubMed] [Google Scholar]
  2. Coen E. S., Dover G. A. Unequal exchanges and the coevolution of X and Y rDNA arrays in Drosophila melanogaster. Cell. 1983 Jul;33(3):849–855. doi: 10.1016/0092-8674(83)90027-2. [DOI] [PubMed] [Google Scholar]
  3. Coen E. S., Thoday J. M., Dover G. Rate of turnover of structural variants in the rDNA gene family of Drosophila melanogaster. Nature. 1982 Feb 18;295(5850):564–568. doi: 10.1038/295564a0. [DOI] [PubMed] [Google Scholar]
  4. Dvorák J., McGuire P. E. Nonstructural Chromosome Differentiation among Wheat Cultivars, with Special Reference to Differentiation of Chromosomes in Related Species. Genetics. 1981 Feb;97(2):391–414. doi: 10.1093/genetics/97.2.391. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Gerlach W. L., Bedbrook J. R. Cloning and characterization of ribosomal RNA genes from wheat and barley. Nucleic Acids Res. 1979 Dec 11;7(7):1869–1885. doi: 10.1093/nar/7.7.1869. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Greene P. J., Heyneker H. L., Bolivar F., Rodriguez R. L., Betlach M. C., Covarrubias A. A., Backman K., Russel D. J., Tait R., Boyer H. W. A general method for the purification of restriction enzymes. Nucleic Acids Res. 1978 Jul;5(7):2373–2380. doi: 10.1093/nar/5.7.2373. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Pellegrini M., Manning J., Davidson N. Sequence arrangement of the rDNA of Drosophila melanogaster. Cell. 1977 Feb;10(2):213–214. doi: 10.1016/0092-8674(77)90215-x. [DOI] [PubMed] [Google Scholar]
  8. Ranzani G. N., Bernini L. F., Crippa M. Inheritance of rDNA spacer length variants in man. Mol Gen Genet. 1984;196(1):141–145. doi: 10.1007/BF00334106. [DOI] [PubMed] [Google Scholar]
  9. Reeder R. H., Brown D. D., Wellauer P. K., Dawid I. B. Patterns of ribosomal DNA spacer lengths are inherited. J Mol Biol. 1976 Aug 25;105(4):507–516. doi: 10.1016/0022-2836(76)90231-x. [DOI] [PubMed] [Google Scholar]
  10. Schalet A. Exchanges at the bobbed locus of Drosophila melanogaster. Genetics. 1969 Sep;63(1):133–153. doi: 10.1093/genetics/63.1.133. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Sharp Z. D., Gandhi V. V., Procunier J. D. X chromosome nucleolus organizer mutants which alter major type I repeat multiplicity in Drosophila melanogaster. Mol Gen Genet. 1983;190(3):438–443. doi: 10.1007/BF00331074. [DOI] [PubMed] [Google Scholar]
  12. Tartof K. D. Redundant genes. Annu Rev Genet. 1975;9:355–385. doi: 10.1146/annurev.ge.09.120175.002035. [DOI] [PubMed] [Google Scholar]

Articles from Genetics are provided here courtesy of Oxford University Press

RESOURCES