Distribution, inheritance and linkage relationships of ribosomal DNA spacer length variants in pea

Abstract

DNA restriction endonuclease fragment analysis is used to examine the genetic organization, inheritance and linkage associations of the ribosomal DNA in pea. The substantial variation observed in the length of the intergenic spacer region is shown to segregate in Mendelian fashion involving two independent genetic loci, designated Rrn1 and Rrn2. Linkage between Rrn1 and two marker loci on chromosome 4 establishes the approximate location of this tandem array. Rrn2 shows linkage with a set of isozyme loci which assort independently of other markers on all seven chromosomes. Combining these observations with previous cytological data, we suggest that Rrn2 and the isozyme loci linked to it constitute a new linkage group on chromosome 7. The general absence of spacer length classes common to both rRNA loci in any of the lines we examined indicates that little or no genetic exchange occurs between the nonhomologous nucleolar organizer regions.

Single-stranded replication intermediates of ribosomal DNA replicons of pea.

“…Alaska (Cullis and Davies, 1975;Ingle and Sinclair, 1972) distributed into two major repeat size classes of 8.6 and 9 kb (Jorgensen et al, 1987). The larger repeat, located on chromosome 7, is more abundant representing -3000 tandem copies or a total of 27 000 kb (Polans et al, 1986;Jorgensen et al, 1987). There are -900 tandem copies or -8000 kb of the smaller repeats on chromosome 4 (Polans et al, 1986;Jorgensen et al, 1987).…”

“…The larger repeat, located on chromosome 7, is more abundant representing -3000 tandem copies or a total of 27 000 kb (Polans et al, 1986;Jorgensen et al, 1987). There are -900 tandem copies or -8000 kb of the smaller repeats on chromosome 4 (Polans et al, 1986;Jorgensen et al, 1987). The repeats are located at or near the nucleolar organizers on their respective chromosomes (J.…”

Variation and inheritance of ribosomal DNA in Pinus sylvestris L. (Scots pine)

“…The proposed molecular mechanisms for maintaining homogeneity include biased and non-biased gene conversion, unequal crossing-over and transposition, which can operate within and between chromosomes (Tartof, 1975;Dover, 1982;Ohta & Dover, 1983. These mechanisms will either eliminate a new variant (the most frequent event in the absence of Previously the inheritance and genetic organization of rDNA variants have been studied in only a few plant species, including Hordeum (Saghai-Maroof et a!., 1984), Pisum sativum (Ellis et at., 1984;Polans et at., 1986) and Triticum (Snape er al., 1985). In each case the rDNA variants were inherited in a regular Mendelian fashion and were distributed non-randomly among rDNA arrays with respect to chromosomal location.…”

“…In each case the rDNA variants were inherited in a regular Mendelian fashion and were distributed non-randomly among rDNA arrays with respect to chromosomal location. The non-random distribution of rDNA variants across loci has been regarded as evidence that the rate of intrachromosomal exchange (homogenization within an rDNA array) is substantially greater than the rate of interchromosomal exchange (Polans et at., 1986). In humans, the marked linkage disequilibrium of rDNA variants within individuals led Seperack eta!.…”

Repeated sequence markers in pea (Pisum sativum)

“…Relativel)^ few of these sequences have been characterized at the DNA sequence level, or in terms of their genomic location (Lee et al, 1990;Ellis et al, 1992;Ellis, 1993). Those repeats which have been characterized are of recognizable DNA sequence classes such as satellite DNAs (Ellis et al, 1989), simple sequence repeats (Lu et al, 1996), 5SrRNA genes (Ellis et al, 1988), rDNA (Ellis et al, 1984;Polans, Weeden & Thompson, 1986), Tycopia like elements (Lee et al, 1990;Flavell, Smith & Kumar, 1992), Ty3-gypsy like elements (Sarup & Stafstrom, 1995), and sequences related to class II transposable elements (Bhattacharyya et al, 1990;Sirsat, 1988;Bown, 1992). From these analyses, the pea genome seems typical of a eukaryotic genome with a size similar to the human genome.…”