Recombination and chiasmata: few but intriguing discrepancies

Abstract

The paradigm that meiotic recombination and chiasmata have the same basis has been challenged, primarily for plants. High resolution genetic mapping frequently results in maps with lengths far exceeding those based on chiasma counts. In addition, recombination between specific homoeologous chromosomes derived from interspecific hybrids is sometimes much higher than can be explained by meiotic chiasma frequencies. However, almost the entire discrepancy disappears when proper care is taken of map inflation resulting from the shortcomings of the mapping algorithm and classification errors, the use of dissimilar material, and the difficulty of accurately counting chiasmata. Still, some exchanges, especially of short interstitial segments, cannot readily be explained by normal meiotic behaviour. Aberrant meiotic processes involving segment replacement or insertion can probably be excluded. Some cases of unusual recombination are somatic, possibly premeiotic exchange. For other cases, local relaxation of chiasma interference caused by small interruptions of homology disturbing synaptonemal complex formation is proposed as the cause. It would be accompanied by a preference for compensating exchanges (negative chromatid interference) resulting from asymmetry of the pairing chromatid pairs, so that one side of each pair preferentially participates in pairing. Over longer distances, the pairing face may switch, causing the normal random chromatid participation in double exchanges and the relatively low frequency of short interstitial exchanges. Key words : recombination frequency, map length, chiasmata, discrepancy, chromatid interference.

Predicting and Testing Physical Locations of Genetically Mapped Loci on Tomato Pachytene Chromosome1

“…In this regard, Khush and Rick (1963) reported examples of mismatched borders of pericentric heterochromatin and mismatched chromomeres at pachytene in the hybrid, and we have observed unilateral buckles, presumably of the S. pennellii lateral elements, in hybrid SCs (our unpublished observations). It is possible that such mispairing and synapsis proximally could obstruct the spread of crossover interference and thereby change crossover patterns and frequencies in the hybrid compared to tomato (Sybenga 1996). On the other hand, markers in the euchromatic part of the short arm and the distal region of the long arm of chromosome 1 are very close to their predicted positions (Figures 2 and 3B, Table 2).…”

Chromosome-Specific Painting in Cucumis Species Using Bulked Oligonucleotides

“…The potential level of recombination between parental genomes was often estimated by analyses of chromosomal pairing and chiasma formation at MI in the hybrids. However, the relationship between meiotic recombination and chiasmata has been a debatable subject, especially in plants (Sybenga 1996). Specifically, recombination between homeologous chromosomes in some interspecific hybrids appeared to be higher than the chiasma frequencies estimated by MI chromosome pairing (Sybenga 1996).…”

“…However, the relationship between meiotic recombination and chiasmata has been a debatable subject, especially in plants (Sybenga 1996). Specifically, recombination between homeologous chromosomes in some interspecific hybrids appeared to be higher than the chiasma frequencies estimated by MI chromosome pairing (Sybenga 1996). For example, cultivated rice (Oryza sativa, AA genomes) chromosomes rarely paired with chromosomes from wild species Oryza officinalis (CC genome) at MI, yet many small interstitial chromosomal segments were transferred from O. officinalis into rice (Jena and Khush 1989;Jena et al 1992).…”

The diverse roles of transverse filaments of synaptonemal complexes in meiosis

“…However, this interpretation does not solve all problems, because cytological interference is unaffected in the yeast ndj1 mutant, which displays wild-type levels of crossing over but reduced genetic interference (Chua and Roeder 1997;Conrad et al 1997). Fung et al (2004) Imunofluorescence background labeling can be mistaken for MLH1 foci Perhaps closely spaced chiasmata involving the same two chromatids disappear by loss of sister chromatid cohesion between the chiasmata (7) In some mutants, chiasmata close to the telomeres may be missed because of loss of sister chromatid cohesion distal to the chiasma (8) Numbers in parentheses represent the following references: 1, reviewed by Sybenga (1996); 2, reviewed by Sybenga (1975); 3, reviewed by Jones (1987); 4, reviewed by Anderson and Stack (2005); 5, Anderson et al (2003);6, Froenicke et al (2002);7, Maguire (1980); and 8, Hodges et al (2005) therefore suggested that there might be more than one interference mechanism: First, an unknown Zip1-independent mechanism would determine the position of ZMM complexes along the bivalent, and subsequently, synapsis, starting from the ZMM complexes, would prevent the formation of ZMM-independent COs near the ZMM complexes. In this view, ZMM-independent (Class II) COs would experience interference, but not exert it.…”