Diploid female gametophyte formation in 24-chromosome potatoes: genetic evidence for the prevalence of the second meiotic division restitution mode

1986 ◽  
Vol 28 (1) ◽  
pp. 101-108 ◽  
Author(s):  
David M. Stelly ◽  
Stanley J. Peloquin
Keyword(s):  
Meiotic Division ◽  
Female Gametophyte ◽  
Alternative Explanation ◽  
Crossing Over ◽  
Mechanism Of Formation ◽  
Tetrad Analysis ◽  
Origin And Evolution ◽  
Diploid Female ◽  
Solanum Spp ◽  
Map Distance

Half-tetrad genetic analysis of 1431 plants in 26 4x potato (Solanum spp.) families from 2x × 4x crosses revealed that at least 20 of the 26 female parents form 2n female gametophytes that are predominantly or exclusively of the second meiotic division restitution (SDR) type. SDR 2n gametophytes genetically equate to gametophytes that would result from restitution of the second meiotic division. Previous estimates obtained by half-tetrad analysis with 2n pollen placed the yellow-tuber flesh marker, Y, at 13 map units from its centromere. Overall ratios observed herein were slightly discordant with predictions based on that estimate, indicating that the map distance (p) may be slightly greater, around 18.5 map units. An alternative explanation is that most of the tested parents produce a mixture of 2n female gametophytes, composed of mostly SDR but also a smaller proportion of FDR or FDR-NCO 2n female gametophytes. Genetically, FDR and FDR-NCO 2n gametophytes equate to those resulting from meiotic first division restitution, with, or with no crossing-over, respectively. Because the data do not discriminate between these hybpotheses, the segregation data were tested according to both estimates of p. Results with six additional clones were inconclusive regarding the mode of 2n gametophyte formation. The results illustrate limitations of half-tetrad analyses for determining the exact composition of 2n gametophyte populations, where these might result from more than one mechanism of formation. The finding that SDR 2n female gametophytes were most prevalent nevertheless supports the hypothesis that they have contributed significantly to the origin and evolution of the tetraploid cultivated potato, and that SDR × FDR or SDR × FDR-NCO crosses (2x × 2x) may be a meritorious approach for potato improvement.Key words: meiosis, Solanum, evolution, breeding.

Use of Neurospora Spore killer strains to obtain centromere linkage data without dissecting asci

1986 ◽  
Vol 28 (6) ◽  
pp. 971-981 ◽  
Author(s):  
David D. Perkins ◽  
Namboori B. Raju ◽  
Virginia C. Pollard ◽  
Joseph L. Campbell ◽  
Adam M. Richman
Keyword(s):  
Meiotic Division ◽  
Nuclear Division ◽  
Linkage Data ◽  
Crossing Over ◽  
Tetrad Analysis ◽  
Marker Alleles ◽  
Spore Killer ◽  
Killer Gene

Use of a centromere-linked Spore killer gene Sk reduces manyfold the labor involved in obtaining tetrad data that would otherwise require ordered dissection of intact linear eight-spored asci. Heterozygous crosses are made for Spore killer (SkK × SkS) and for markers to be tested. In such crosses only SkK ascospores survive. The four viable (SkK) and four aborted (SkS) ascospores of each ascus are ejected from the perithecium as a physically disordered group. The four surviving SkK ascospores of individual asci are germinated and scored. SkK segregates from SkS at the first meiotic division. If both marker alleles are represented in the surviving products, they must therefore have segregated from one another at the second division. Four-spore (Fsp) genes have been used to eliminate one postmeiotic nuclear division, so that only two ascospores per ascus need to be scored. The Spore killer method has been useful for mapping closely linked genes in centromere regions, for identifying genes that are far out on chromosome arms, for obtaining information on meiotic crossing-over, and for comparing linkages in different species.Key words: tetrad analysis, centromere mapping, Spore killer, Neurospora.

scholarly journals Gene conversion: observations on the DNA hybrid models

1970 ◽  
Vol 15 (1) ◽  
pp. 55-64 ◽  
Author(s):  
Andrzej Paszewski
Keyword(s):  
Experimental Data ◽  
Gene Conversion ◽  
Hybrid Models ◽  
Crossing Over ◽  
Meiotic Segregation ◽  
Tetrad Analysis ◽  
Dna Models ◽  
Complex Picture ◽  
New Hypothesis ◽  
Hybrid Dna

SUMMARYSome features of gene conversion in fungi and their bearing on the hybrid DNA models are discussed. Available experimental data from tetrad analysis seem to give a more complex picture of polarity in intra-genic recombination and of the relations between conversion and post-meiotic segregation, and between conversion and crossing-over, than predicted by the models.A new hypothesis of the mechanism of gene conversion with special attention given to the aspect of asymmetry in this phenomenon is proposed as an alternative to the mechanism suggested by the DNA hybrid models.

scholarly journals The Ade6-M26 Mutation of Schizosaccharomyces Pombe Increases the Frequency of Crossing over.

Genetics ◽  
1988 ◽  
Vol 119 (3) ◽  
pp. 507-515
Author(s):  
P Schuchert ◽  
J Kohli
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Marker Gene ◽  
Crossing Over ◽  
Crossover Frequency ◽  
Tetrad Analysis ◽  
Ectopic Recombination ◽  
Homologous Sequences ◽  
New Information ◽  
Conversion Frequency

Abstract The ade6-M26 mutation of Schizosaccharomyces pombe increases conversion frequency in comparison with the nearby mutation ade6-M375. In order to investigate the effect of ade6-M26 on crossover frequency, heteroallelic ade6 duplications were constructed by integration of plasmids carrying the marker gene ura4. One ade6 gene carries either of the mutations M26 or M375 while the other ade6 copy carries the L469 mutation in both duplications. The duplication with ade6-M26 yields Ade(+) recombinants at significantly higher frequencies in meiosis, but not in mitosis. Tetrad analysis and physical characterization of spore clones from recombination tetrads demonstrate that conversions, unequal crossovers and intrachromatid exchanges occur at higher frequencies but with unaltered proportions among them. The conversion events show a pronounced bias when M26 is involved: they take place preferentially at the M26 allele. Thus the ade6-M26 mutation not only enhances conversion frequency as demonstrated before, but also crossover frequency. It displays the properties expected for a preferred site of initiation of general meiotic recombination. The duplications also yielded new information on ectopic recombination in S. pombe: ectopic crossovers occur in the duplications at much higher frequency than among naturally dispersed homologous sequences.

scholarly journals Memoirs: The Male Meiotic Phase in Two Genera of Marsupials (Macropus and Petauroides)

1923 ◽  
Vol s2-67 (266) ◽  
pp. 183-202
Author(s):  
W. E. AGAR
Keyword(s):  
Chromosome Number ◽  
Sex Chromosomes ◽  
Meiotic Division ◽  
Ovarian Follicle ◽  
The Other ◽  
Pachytene Stage ◽  
Follicle Cells ◽  
Crossing Over ◽  
Early Pachytene ◽  
Spermatogonial Metaphase

Macropus ualabatus has twelve chromosomes, namely 10 + XY in the male and 10 + XX in the female. In Petauroides the number is almost certainly twenty-two, the male being of the formula 20 + XY. No female counts were obtained for this animal. In the male Macropus Xis generally attached to one of the autosomes in spermatogonial mitoses. Y, which is exceedingly minute, is free. During the pachytene stage, while the autosomes are still elongated, X and Y condense into a bivalent. In the first meiotic division this bivalent is attached to an autosome. As a result of the first meiotic division the usual two classes of secondary spermatocytes are formed one with X and the other with Y. In the second meiotic division, those with X show only five separate chromosomes, showing that X, as usual, is fused with an autosome. The other class of second divisions shows five autosomes and the minute Y. In the female Macropus the sex chromosomes were never found free from the autosomes in the ovarian follicle cells, which therefore show only ten separate chromosomes. In Petauroides the sex chromosomes cannot be distinguished with certainty from the autosomes. An unequal pair of small chromosomes usually situated in the centre of the spermatogonial metaphase plates probably, however, are X and Y. Early pachytene nuclei show two compact bodies which unite into one, presumably the sex bivalent. The second reduction of the chromosome number to onequarter of the diploid total in the second meiotic division, which has been described for several species of birds and mammals, does not take place either in Macropus or Petauroides. Chromomeres are very prominent in Petauroides in the zygotene and diplotene stages. Probably in Macropus, and more convincingly in Petauroides, the cytological conditions to permit of ‘crossing over’ are present in the male. The plasmosome which appears in the pachytene stage is probably formed from the plastin or linin basis of the contracting sex chromosomes.

Gene-centromere mapping in potato by half-tetrad analysis: map distances of H1, Rx, and Ry and their possible use for ascertaining the mode of 2n-pollen formation

Genome ◽  
1992 ◽  
Vol 35 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Marinus Wagenvoort ◽  
Ewa Zimnoch-Guzowska
Keyword(s):  
Potato Virus ◽  
Potato Virus Y ◽  
Potato Virus X ◽  
2N Pollen ◽  
Tetrad Analysis ◽  
Extreme Resistance ◽  
Second Division Restitution ◽  
Pollen Formation ◽  
Tetraploid Progeny ◽  
Map Distance

Diploids from the tetraploid potato varieties 'Alcmaria' and 'Pansta' and from the tetraploid CPRO genotypes Y66-13-610 and Y66-13-636 were used in half-tetrad analyses to estimate the gene-centromere map distances of the genes Rx, Ry, and H1. Employing tetraploid progeny from 2x (second division restitution) – 4x testcrosses the gene-centromere map distance of H1, conferring resistance to pathotype Ro1 of Globodera rostochiensis, was estimated to be 16.3 centimorgans (cM). For Rχ, conferring extreme resistance to potato virus X (PVX), a map distance of 33.9 cM was estimated. The gene Ry, conferring extreme resistance to potato virus Y (PVY), was estimated to be located 14.2 cM from the centromere. Using the estimated map distance for Rx, it was attempted to determine the mode of 2n-pollen formation in four diploid interspecific hybrids, including the species Solanum tuberosum, Solanum chacoense, Solanum yungasense, and Solanum phureja, by half-tetrad analysis in tetraploid progeny from 4x-2x testcrosses. The mean frequency of 8.7% nulliplex plants for Rx was outside the range of the 95% confidence intervals, for both first division restitution and second division restitution 2n pollen.Key words: nematode resistance, potato virus X resistance, potato virus Y resistance, 2n eggs, gene-centromere mapping, Solanum.

scholarly journals Sexual dimorphism in mouse gametogenesis

1960 ◽  
Vol 1 (3) ◽  
pp. 477-486 ◽  
Author(s):  
B. M. Slizynski
Keyword(s):  
Sexual Dimorphism ◽  
Meiotic Division ◽  
Chiasma Formation ◽  
Meiotic Metaphase ◽  
Pachytene Stage ◽  
Crossing Over ◽  
Adult Males ◽  
Present Technique ◽  
Metaphase Stage ◽  
Gametic Selection

Diplotene and diakinesis chiasma frequency in oöcytes of the mouse cannot be studied successfully with the present technique. Metaphase chiasmata have been examined in thirty-nine oöcytes. It is deduced that the total diplotene map length in females is about 2300 cM. compared with 1950 cM. in males. There is sexual dimorphism in the frequency of chiasmata, which is paralleled by similar dimorphism in frequencies of crossing-over, measured genetically.The two sexes differ in the duration of various stages of meiosis. In adult males the pachytene stage, lasting for about 7 days, is directly followed by diplotene and diakinesis, after which the metaphase stage sets in. The sex bivalent in males develops visible chiasmata much earlier than do the autosomes and it precedes them in anaphase separation. Quick terminalization of chiasmata in it leads in a fair proportion of cases to precocious separation and in less than 1% of cases to cytologically detectable non-disjunction of sex chromosomes.In females the pachytene stage appears in oöcytes of the embryo and is followed by the dictyotene stage, which last still ovulation, i.e. between 35–40 days and several months. Since in the oöcyte chiasmata are formed and move during the dictyotene stage, it follows that stainable materials of the chromosomes are not necessary for the formation and movement of chiasmata and are concomitant with pairing and anaphase separation. It follows also that the time for chiasma formation and movement is in females at least five to six times longer than in males. In old oöcytes in which time is available for maximum terminalization of chiasmata, non-disjunction may appear with detectable frequency. This mechanism may also operate in cases of Mongolism in man, where non-disjunction of an autosome has been recently cytologically established and higher frequency of incidence of the condition for old mothers has been known for some time.It is possible that the differences in duration of various stages of gametogenesis are connected with the period at which gametic selection is operating: in spermatogenesis after the second meiotic division, in oögenesis prior to first meiotic metaphase.

Variation in "Map Distance" in Neurospora crassa

1969 ◽  
Vol 15 (6) ◽  
pp. 623-627 ◽  
Author(s):  
Mary B. Mitchell
Keyword(s):  
Life Cycle ◽  
Neurospora Crassa ◽  
Crossing Over ◽  
General Behavior ◽  
Phenotype Distribution ◽  
Random Distributions ◽  
Detailed Interpretation ◽  
Chromosome Segments ◽  
Map Distance

Determinations of the same map distance in different crosses often give divergent results, whereas values for unrelated map regions are often strikingly similar. This situation has been examined in samples of serially isolated spore octets, mainly from two-marker crosses. Observed ratios of phenotype distribution classes suggest more systematic modifications of random distributions than would be expected from reassociations, through crossing-over, of chromosome segments chosen unsystematically. Detailed interpretation appears impracticable, since complexities in the general behavior of the organism indicate that the ratios observed may reflect opportunities, occurring at different stages of the life cycle, for successive reassociations of genetic units.

scholarly journals MAPPING AND GENE CONVERSION STUDIES WITH THE STRUCTURAL GENE FOR ISO-1-CYTOCHROME C IN YEAST

Genetics ◽  
1975 ◽  
Vol 81 (4) ◽  
pp. 615-629
Author(s):  
Christopher W Lawrence ◽  
Fred Sherman ◽  
Mary Jackson ◽  
Richard A Gilmore
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Gene Conversion ◽  
The Other ◽  
Crossing Over ◽  
Wild Type ◽  
Chromosome X ◽  
Tetrad Analysis ◽  
Yeast Saccharomyces Cerevisiae ◽  
Distal Marker ◽  
The Right

ABSTRACT We have investigated the order of the four genes cyc1, rad7, SUP4, and cdc8 which form a tightly linked cluster on the right arm of chromosome X in the yeast Saccharomyces cerevisiae. Crossing over and coconversion data from tetrad analysis established the gene order to be centromere–cyc1–rad7–SUP4. Also cdc8 appeared to be distal to SUP4 on the basis of crossovers that were associated with conversion of SUP4. The frequencies of recombination and the occurrence of coconversions suggest that these four genes are contiguous or at least nearly so. Gene-conversion frequencies for several cyc1 alleles were studied, including cyc1–1, a deletion of the whole gene that extends into the rad7 locus. The cyc1–1 deletion was found to be capable of conversion, though at a frequency some fivefold less than the other alleles studied, and both 3:1 and 1:3 events were detected. In general 1:3 and 3:1 conversion events were equally frequent at all loci studied, and approximately 50% of conversions were accompanied by reciprocal recombination for flanking markers. The orientation of the cyc1 gene could not be clearly deduced from the behavior of the distal marker SUP4 in wild-type recombinants that arose from diploids heteroallelic for cyc1 mutations.

scholarly journals mlh3 separation of function and endonuclease defective mutants display an unexpected effect on meiotic recombination outcomes

2017 ◽  
Author(s):  
Najla Al-Sweel ◽  
Vandana Raghavan ◽  
Abhishek Dutta ◽  
V. P. Ajith ◽  
Luigi Di Vietro ◽  
...  
Keyword(s):  
Dna Replication ◽  
Mismatch Repair ◽  
Protein Interactions ◽  
Meiotic Recombination ◽  
Meiotic Division ◽  
Dna Mismatch Repair ◽  
Crossing Over ◽  
Baker's Yeast ◽  
Protein Protein Interactions ◽  
Dna Mismatch

AbstractMlh1-Mlh3 is an endonuclease hypothesized to act in meiosis to resolve double Holliday junctions into crossovers. It also plays a minor role in eukaryotic DNA mismatch repair (MMR). To understand how Mlh1-Mlh3 functions in both meiosis and MMR, we analyzed in baker’s yeast 60 new mlh3 alleles. Five alleles specifically disrupted MMR, whereas one (mlh3-32) specifically disrupted meiotic crossing over. Mlh1-mlh3 representatives for each separation of function class were purified and characterized. Both Mlh1-mlh3-32 (MMR+, crossover-) and Mlh1-mlh3-45 (MMR-, crossover+) displayed wild-type endonuclease activities in vitro. Msh2-Msh3, an MSH complex that acts with Mlh1-Mlh3 in MMR, stimulated the endonuclease activity of Mlh1-mlh3-32 but not Mlh1-mlh3-45, suggesting that Mlh1-mlh3-45 is defective in MSH interactions. Whole genome recombination maps were constructed for two mlh3 mutants with opposite separation of function phenotypes, and an endonuclease defective mutant. Unexpectedly, all three showed increases in the number of non-crossover events that were not observed in mlh3Δ. Our observations provide a structure-function map for Mlh3 that reveals the importance of protein-protein interactions in regulating Mlh1-Mlh3’s enzymatic activity. They also illustrate how defective meiotic components can alter the fate of meiotic recombination intermediates, providing new insights for how meiotic recombination pathways are regulated.Author SummaryDuring meiosis, diploid germ cells that become eggs or sperm undergo a single round of DNA replication followed by two consecutive chromosomal divisions. The segregation of chromosomes at the first meiotic division is dependent in most organisms on at least one genetic exchange, or crossover event, between chromosome homologs. Homologs that do not receive a crossover frequently undergo non-disjunction at the first meiotic division, yielding gametes that lack chromosomes or contain additional copies. Such events have been linked to human disease and infertility. Recent studies suggest that the Mlh1-Mlh3 complex is an endonuclease that resolves recombination intermediates into crossovers. Interestingly, this complex also acts as a matchmaker in DNA mismatch repair (MMR) to remove DNA replication errors. How does one complex act in two different processes? We investigated this question by performing a mutational analysis of the baker’s yeast Mlh3 protein. Five mutations were identified that disrupted MMR but not crossing over, and one mutation disrupted crossing over while maintaining MMR. Using a combination of biochemical and genetic analyses to further characterize these mutants we illustrate the importance of protein-protein interactions for Mlh1-Mlh3’s activity. Importantly, we illustrate how defective meiotic components can alter the outcome of meiotic recombination events. They also provide new insights in our understanding of the basis of infertility syndromes.

scholarly journals Premeiotic change of nucleolus organizer size in Neurospora.

Genetics ◽  
1989 ◽  
Vol 122 (4) ◽  
pp. 783-791 ◽  
Author(s):  
D K Butler ◽  
R L Metzenberg
Keyword(s):  
Neurospora Crassa ◽  
Gel Electrophoresis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Pulsed Field Gel Electrophoresis ◽  
Crossing Over ◽  
Tetrad Analysis ◽  
Homologous Chromosomes ◽  
Unequal Crossing Over

Abstract We have investigated the heritability of nucleolus organizer region (NOR) size in Neurospora crassa. By pulsed-field gel electrophoresis, we followed in genetic crosses the size of the normal or "terminal" NORs and the size of a small interstitial NOR. Tetrad analysis revealed that changes in NOR size occur frequently in the sexual phase. Moreover, most size changes occurred in the period between fertilization and meiosis, although some changes occurred during and after meiosis. Unexpectedly, increases and decreases in NOR size were not equally frequent: decreases were more common. The NOR size changes generated during meiosis were not the result of unequal crossing over between NORs on homologous chromosomes.

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