Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards

Homologous recombination pathways probably evolved primarily to accomplish chromosomal repair and the formation and resolution of duplications by sister-chromosome exchanges. Various DNA lesions initiate these events. Classical recombination assays, involving bacterial sex, focus attention on double-strand ends of DNA. Sexual exchanges, initiated at these ends, depend on the RecBCD pathway. In the absence of RecBCD function, mutation of the sbcB and sbcC genes activates the apparently cryptic RecF pathway. To provide a more general view of recombination, we describe an assay in which endogenous DNA damage initiates recombination between chromosomal direct repeats. The repeats flank markers conferring lactose utilization (Lac+) and ampicillin resistance (ApR); recombination generates Lac-ApS segregants. In this assay, the RecF pathway is not cryptic; it plays a major role without sbcBC mutations. Others have proposed that single-strand gaps are the natural substrate for RecF-dependent recombination. Supporting this view, recombination stimulated by a double-strand break (DSB) in a chromosomal repeat depended on RecB function, not RecF function. Without RecBCD function, sbcBC mutations modified the RecF pathway and allowed it to catalyze DSB-stimulated recombination. Sexual recombination assays overestimate the importance of RecBCD and DSBs, and underestimate the importance of the RecF pathway.

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A Comparative Analysis of Chromosome Pairing at Metaphase I in Interspecific Hybrids between Durum Wheat (Triticum turgidum L.) and the Most Widespread Aegilops Species

Cytogenetic and Genome Research ◽

10.1159/000313593 ◽

2010 ◽

Vol 129 (1-3) ◽

pp. 124-132 ◽

Cited By ~ 4

Author(s):

M. Cifuentes ◽

V. Garcia-Agüero ◽

E. Benavente

Keyword(s):

Comparative Analysis ◽

Durum Wheat ◽

Chromosome Pairing ◽

Interspecific Hybrids ◽

Triticum Turgidum ◽

Metaphase I

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Detecting Nature of Chromosome Pairing in A and E Genomes of Oryza

CYTOLOGIA ◽

10.1508/cytologia.74.223 ◽

2009 ◽

Vol 74 (2) ◽

pp. 223-227

Author(s):

Fida Mohammad Abbasi ◽

Habib Ahmad ◽

Mohammad Sajid ◽

Inamullah ◽

Darshan Singh Brar

Keyword(s):

Chromosome Pairing

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Chromosome pairing in female and male diploid and polyploid anurans (Amphibia) from South America

Canadian Journal of Genetics and Cytology ◽

10.1139/g83-073 ◽

1983 ◽

Vol 25 (5) ◽

pp. 487-494

Author(s):

I. M. Rahn ◽

A. Martinez

Keyword(s):

South America ◽

Genetic Control ◽

Chromosome Pairing ◽

Diploid Males ◽

Terminal Chiasmata

Chromosome pairing in females and males of diploid (2n = 22) and tetraploid (2n = 44) Odontophrynus americanus and diploid Ceratophrys cranwelli (2n = 26) and tetraploid C. ornata (2n = 104) showed that diploid females formed more chiasmata per paired arm than diploid males and polyploids of both sexes. There was a reduction in the level of recombination in female polyploids by forming multivalents with terminal chiasmata. The reduction reflected a change in the genetic control of pairing in females after polyploidization.

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Synthesis and cytological characterization of trigeneric hybrids of durum wheat with and without Ph1

Genome ◽

10.1139/g04-082 ◽

2004 ◽

Vol 47 (6) ◽

pp. 1173-1181 ◽

Cited By ~ 28

Author(s):

Prem P Jauhar ◽

M Doğramaci ◽

T S Peterson

Keyword(s):

In Situ Hybridization ◽

Chromosome Pairing ◽

Genetic Recombination ◽

Genomic In Situ Hybridization ◽

Homoeologous Pairing ◽

Alien Gene Transfer ◽

Chromosome 5B ◽

Alien Gene ◽

Trigeneric Hybrids

Wild grasses in the tribe Triticeae, some in the primary or secondary gene pool of wheat, are excellent reservoirs of genes for superior agronomic traits, including resistance to various diseases. Thus, the diploid wheatgrasses Thinopyrum bessarabicum (Savul. and Rayss) Á. Löve (2n = 2x = 14; JJ genome) and Lophopyrum elongatum (Host) Á. Löve (2n = 2x = 14; EE genome) are important sources of genes for disease resistance, e.g., Fusarium head blight resistance that may be transferred to wheat. By crossing fertile amphidiploids (2n = 4x = 28; JJEE) developed from F1 hybrids of the 2 diploid species with appropriate genetic stocks of durum wheat, we synthesized trigeneric hybrids (2n = 4x = 28; ABJE) incorporating both the J and E genomes of the grass species with the durum genomes A and B. Trigeneric hybrids with and without the homoeologous-pairing suppressor gene, Ph1, were produced. In the absence of Ph1, the chances of genetic recombination between chromosomes of the 2 useful grass genomes (JE) and those of the durum genomes (AB) would be enhanced. Meiotic chromosome pairing was studied using both conventional staining and fluorescent genomic in situ hybridization (fl-GISH). As expected, the Ph1-intergeneric hybrids showed low chromosome pairing (23.86% of the complement), whereas the trigenerics with ph1b (49.49%) and those with their chromosome 5B replaced by 5D (49.09%) showed much higher pairing. The absence of Ph1 allowed pairing and, hence, genetic recombination between homoeologous chromosomes. Fl-GISH analysis afforded an excellent tool for studying the specificity of chromosome pairing: wheat with grass, wheat with wheat, or grass with grass. In the trigeneric hybrids that lacked chromosome 5B, and hence lacked the Ph1 gene, the wheat–grass pairing was elevated, i.e., 2.6 chiasmata per cell, a welcome feature from the breeding standpoint. Using Langdon 5D(5B) disomic substitution for making trigeneric hybrids should promote homoeologous pairing between durum and grass chromosomes and hence accelerate alien gene transfer into the durum genomes.Key words: alien gene transfer, chiasma (xma) frequency, chromosome pairing, fluorescent genomic in situ hybridization (fl-GISH), homoeologous-pairing regulator, specificity of chromosome pairing, wheatgrass.

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PrBn, a Major Gene Controlling Homeologous Pairing in Oilseed Rape (Brassica napus) Haploids

Genetics ◽

10.1093/genetics/164.2.645 ◽

2003 ◽

Vol 164 (2) ◽

pp. 645-653 ◽

Cited By ~ 4

Author(s):

Eric Jenczewski ◽

Frédérique Eber ◽

Agnès Grimaud ◽

Sylvie Huet ◽

Marie Odile Lucas ◽

...

Keyword(s):

Brassica Napus ◽

Oilseed Rape ◽

Chromosome Pairing ◽

Major Gene ◽

Major Effect ◽

F1 Hybrids ◽

Precise Control ◽

Ph1 Locus ◽

Likelihood Approach ◽

Likelihood Ratio Statistics

Abstract Precise control of chromosome pairing is vital for conferring meiotic, and hence reproductive, stability in sexually reproducing polyploids. Apart from the Ph1 locus of wheat that suppresses homeologous pairing, little is known about the activity of genes that contribute to the cytological diploidization of allopolyploids. In oilseed rape (Brassica napus) haploids, the amount of chromosome pairing at metaphase I (MI) of meiosis varies depending on the varieties the haploids originate from. In this study, we combined a segregation analysis with a maximum-likelihood approach to demonstrate that this variation is genetically based and controlled mainly by a gene with a major effect. A total of 244 haploids were produced from F1 hybrids between a high- and a low-pairing variety (at the haploid stage) and their meiotic behavior at MI was characterized. Likelihood-ratio statistics were used to demonstrate that the distribution of the number of univalents among these haploids was consistent with the segregation of a diallelic major gene, presumably in a background of polygenic variation. Our observations suggest that this gene, named PrBn, is different from Ph1 and could thus provide complementary information on the meiotic stabilization of chromosome pairing in allopolyploid species.

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Inferences from genetical evidence on the course of meiotic chromosome pairing in plants

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1977.0020 ◽

1977 ◽

Vol 277 (955) ◽

pp. 313-326 ◽

Cited By ~ 28

Keyword(s):

Chromosome Pairing ◽

Developmental Stages ◽

Meiotic Chromosome ◽

Critical Assessment ◽

Gene Control ◽

Meiotic Pairing ◽

Homologous Chromosomes ◽

Meiotic Chromosome Pairing ◽

Combined Use ◽

Or Gene

Meiotic chromosome pairing is a process that is amenable to genetic and experimental analysis. The combined use of these two approaches allows for the process to be dissected into several finite periods of time in which the developmental stages of pairing can be precisely located. Evidence is now available, in particular in plants, that shows that the pairing of homologous chromosomes, as observed at metaphase I, is affected by events occurring as early as the last premeiotic mitosis; and that the maintenance of this early determined state is subsequently maintained by constituents (presumably proteins) that are sensitive to either colchicine, temperature or gene control. A critical assessment of this evidence in wheat and a comparison of the process of pairing in wheat with the course of meiotic pairing in other plants and animals is presented.

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