MEIOTIC NONDISJUNCTION AND ANEUPLOIDS IN INTERSYNGENIC HYBRIDS OF PARAMECIUM CAUDATUM

Genetics ◽  
1985 ◽  
Vol 111 (4) ◽  
pp. 779-794
Author(s):  
Yuuji Tsukii ◽  
Koichi Hiwatashi
Keyword(s):  
Mating Type ◽  
Genetic Study ◽  
F1 Hybrids ◽  
Crossing Over ◽  
Paramecium Caudatum ◽  
Meiotic Process ◽  
Unequal Crossing Over ◽  
Meiotic Nondisjunction ◽  
Fertile Hybrids

ABSTRACT Artificially induced intersyngenic crosses in Paramecium caudatum can produce viable and fertile hybrids. When F1 hybrids of double E mating type (Mt  1/Mt  3 or Mt  12/Mt  3) were crossed with mating type O (mt/mt), aberrant segregants of double E and single O type were produced. This segregation was not explained by ordinary equal or unequal crossing over. Breeding analyses of these segregants by using linkage between Mt and cnrA (a behavioral mutant) revealed that they were produced by meiotic nondisjunction of bivalent chromosomes carrying Mt genes, and thus the double E and single O segregants were aneuploids: trisomics (Mt  1/Mt  3/mt or Mt  12/Mt  3/mt) and monosomics (mt), respectively. An aberrant segregant was also obtained for another locus, tnd 2, independent of both Mt and cnrA, suggesting the occurrence of meiotic nondisjunction throughout hybrid genomes. These aneuploids will be useful for genetic study in this species. The occurrence of meiotic nondisjunction in the intersyngenic hybrids also suggests that syngens of P. caudatum have been reproductively isolated for long enough to develop chromosomal incompatibility in their meiotic process.

Mapping Unequal Crossing over Hotspot Region of Simple Sequence Repeat in Maize

2009 ◽  
Vol 35 (5) ◽  
pp. 958-961
Author(s):  
Ji-Hua TANG ◽  
Xi-Qing MA ◽  
Wen-Tao TENG ◽  
Jian-Bing YAN ◽  
Jing-Rui DAI ◽  
...  
Keyword(s):  
Simple Sequence Repeat ◽  
Crossing Over ◽  
Sequence Repeat ◽  
Unequal Crossing Over ◽  
Simple Sequence

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

scholarly journals Recombinogenic Effects of Suppressors of Position-Effect Variegation in Drosophila

Genetics ◽  
2002 ◽  
Vol 160 (2) ◽  
pp. 609-621
Author(s):  
Thomas Westphal ◽  
Gunter Reuter
Keyword(s):  
Chromatin Structure ◽  
Position Effect ◽  
Heterochromatic Region ◽  
Crossing Over ◽  
Position Effect Variegation ◽  
Chromosome 2 ◽  
Additive Effects ◽  
Suppressor Mutations ◽  
Effect Variegation ◽  
Meiotic Nondisjunction

Abstract Compact chromatin structure, induction of gene silencing in position-effect variegation (PEV), and crossing-over suppression are typical features of heterochromatin. To identify genes affecting crossing-over suppression by heterochromatin we tested PEV suppressor mutations for their effects on crossing over in pericentromeric regions of Drosophila autosomes. From the 46 mutations (28 loci) studied, 16 Su(var) mutations of the nine genes Su(var)2-1, Su(var)2-2, Su(var)2-5, Su(var)2-10, Su(var)2-14, Su(var) 2-15, Su(var)3-3, Su(var)3-7, and Su(var)3-9 significantly increase in heterozygotes or by additive effects in double and triple heterozygotes crossing over in the ri-pp region of chromosome 3. Su(var)2-201 and Su(var) 2-1401 display the strongest recombinogenic effects and were also shown to enhance recombination within the light-rolled heterochromatic region of chromosome 2. The dominant recombinogenic effects of Su(var) mutations are most pronounced in proximal euchromatin and are accompanied with significant reduction of meiotic nondisjunction. Our data suggest that crossing-over suppression by heterochromatin is controlled at chromatin structure as well as illustrate the possible effects of heterochromatin on total crossing-over frequencies in the genome.

Unequal Crossing-over in Unique PABP2 Mutations in Japanese Patients

2002 ◽  
Vol 59 (3) ◽  
pp. 474 ◽  
Author(s):  
Mika Nakamoto ◽  
Satoshi Nakano ◽  
Shingo Kawashima ◽  
Masafumi Ihara ◽  
Yo Nishimura ◽  
...  
Keyword(s):  
Japanese Patients ◽  
Crossing Over ◽  
Unequal Crossing Over

scholarly journals Possible role of natural selection in the formation of tandem-repetitive noncoding DNA.

Genetics ◽  
1994 ◽  
Vol 136 (1) ◽  
pp. 333-341
Author(s):  
W Stephan ◽  
S Cho
Keyword(s):  
Natural Selection ◽  
Satellite Dna ◽  
Repeat Length ◽  
Crossing Over ◽  
Recombination Rates ◽  
Noncoding Dna ◽  
Satellite Dnas ◽  
Unequal Crossing Over ◽  
Wide Range ◽  
Long Range Ordering

Abstract A simulation model of sequence-dependent amplification, unequal crossing over and mutation is analyzed. This model predicts the spontaneous formation of tandem-repetitive patterns of noncoding DNA from arbitrary sequences for a wide range of parameter values. Natural selection is found to play an essential role in this self-organizing process. Natural selection which is modeled as a mechanism for controlling the length of a nucleotide string but not the sequence itself favors the formation of tandem-repetitive structures. Two measures of sequence heterogeneity, inter-repeat variability and repeat length, are analyzed in detail. For fixed mutation rate, both inter-repeat variability and repeat length are found to increase with decreasing rates of (unequal) crossing over. The results are compared with data on micro-, mini- and satellite DNAs. The properties of minisatellites and satellite DNAs resemble the simulated structures very closely. This suggests that unequal crossing over is a dominant long-range ordering force which keeps these arrays homogeneous even in regions of very low recombination rates, such as at satellite DNA loci. Our analysis also indicates that in regions of low rates of (unequal) crossing over, inter-repeat variability is maintained at a low level at the expense of much larger repeat units (multimeric repeats), which are characteristic of satellite DNA. In contrast, the microsatellite data do not fit the proposed model well, suggesting that unequal crossing over does not act on these very short tandem arrays.

scholarly journals Antifungal activity of Rauwolfia serpentina root extract against Neurospora crassa and genetic study of induced mutants

2019 ◽  
Vol 54 (3) ◽  
pp. 241-246
Author(s):  
AL Ray
Keyword(s):  
Antifungal Activity ◽  
Neurospora Crassa ◽  
Mating Type ◽  
Genetic Study ◽  
Nuclear Gene ◽  
Segregation Ratio ◽  
Root Extract ◽  
Rauwolfia Serpentina ◽  
Induced Mutants ◽  
Morphological Mutants

Rauwolfia serpentina (R. serpentina) root extract was used to study antifungal activity against Neurospora crassa (Ema) as well as mutation, mating type, segregation of the fungus. It was found that more concentration of root extract was used in VM media, higher antifungal activity was observed. After mutation in N. crassa conidia with root extract of R. serpentina, 5 groups of morphological mutants viz. albino (al 98), vigorous (vg 77), fluffy (fl 139), conidial band (con.band 221) and cauliflower (clf 155) were obtained. From genetic study, it was found that all the mutants formed perithecia crossing with EmA which confirmed that mating type of all the mutants is ‘a’ and is not changed due to mutation. Besides, segregation ratio between mutant and wild isolates was about 1:1 which confirmed that mutation takes place in the nuclear gene, not cytoplasmic. Bangladesh J. Sci. Ind. Res.54(3), 241-246, 2019

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