Pericentric inversion in natural populations of Oligoryzomys nigripes (Rodentia: Sigmodontinae)

Genome ◽  
2001 ◽  
Vol 44 (5) ◽  
pp. 791-796 ◽  
Author(s):  
Cibele R Bonvicino ◽  
Paulo S D'Andrea ◽  
Pavel M Borodin
Keyword(s):  
Electron Microscopy ◽  
Pericentric Inversion ◽  
Natural Populations ◽  
Chromosome 3 ◽  
Crossing Over ◽  
Inverted Region ◽  
Meiotic Analysis ◽  
Hardy Weinberg Equilibrium ◽  
Heterozygous Carriers ◽  
Nonhomologous Synapsis

We analysed polymorphism for pericentric inversion in chromosome 3 of Oligoryzomys nigripes (Rodentia: Sigmodontinae) in several populations in Brazil and examined the meiotic behaviour of this chromosome in heterozygotes. We observed an orderly pairing of all chromosomes at pachytene in heterozygotes for the inverted chromosome 3. No indication of meiotic arrest and germ-cell death was found. Electron microscopy of synaptonemal complexes and conventional meiotic analysis indicated strictly nonhomologous synapsis and crossing-over suppression in the inverted region in the heterozygotes, which prevent the formation of unbalanced gametes. Thus, the pericentric inversion in chromosome 3 does not apparently result in any selective disadvantages in heterozygous carriers. In the majority of the populations studied, the frequencies of acrocentric homozygotes, metacentric homozygotes, and heterozygotes were in Hardy–Weinberg equilibrium. However, in some populations, we detected an excess of heterozygotes and a deficiency of acrocentric homozygotes.Key words: chromosome rearrangements, inversion, meiosis, Oligoryzomys nigripes.

scholarly journals Lack of underdominance in a naturally occurring pericentric inversion in Drosophila melanogaster and its implications for chromosome evolution.

Genetics ◽  
1991 ◽  
Vol 129 (3) ◽  
pp. 791-802
Author(s):  
J A Coyne ◽  
S Aulard ◽  
A Berry
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Genetic Drift ◽  
Related Species ◽  
Pericentric Inversion ◽  
Chromosome Evolution ◽  
Natural Populations ◽  
Crossing Over ◽  
Closely Related Species ◽  
Naturally Occurring

Abstract In(2LR)PL is a large pericentric inversion polymorphic in populations of Drosophila melanogaster on two Indian Ocean islands. This polymorphism is puzzling: because crossing over in female heterokaryotypes produces inviable zygotes, such inversions are thought to be underdominant and should be quickly eliminated from populations. The observed fixation for such inversions among related species has led to the idea that genetic drift can cause chromosome evolution in opposition to natural selection. We found, however, that In(2LR)PL is not underdominant for fertility, as heterokaryotypic females produce perfectly viable eggs. Genetic analysis shows that the lack of underdominance results from the nearly complete absence of crossing over in the inverted region. This phenomenon is probably caused by mechanical and not genetic factors, because crossing over is not suppressed in In(2LR)PL homokaryotypes. Our observations do not support the idea that the fixation of pericentric inversions among closely related species implies the action of genetic drift overcoming strong natural selection in very small populations. If chromosome arrangements vary in their underdominance, it is those with the least disadvantage as heterozygotes, like In(2LR)PL, that will be polymorphic or fixed in natural populations.

High-voltage electron microscopy of maxillary gland of spirochete-infected brine shrimp: lesion of efferent tubule

1988 ◽  
Vol 46 ◽  
pp. 362-363
Author(s):  
G. E. Tyson ◽  
M. J. Song
Keyword(s):  
Electron Microscopy ◽  
High Voltage ◽  
Brine Shrimp ◽  
Natural Populations ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Infected Adult

Natural populations of the brine shrimp, Artemia, may possess spirochete- infected animals in low numbers. The ultrastructure of Artemia's spirochete has been described by conventional transmission electron microscopy. In infected shrimp, spirochetal cells were abundant in the blood and also occurred intra- and extracellularly in the three organs examined, i.e. the maxillary gland (segmental excretory organ), the integument, and certain muscles The efferent-tubule region of the maxillary gland possessed a distinctive lesion comprised of a group of spirochetes, together with numerous small vesicles, situated in a cave-like indentation of the base of the tubule epithelium. in some instances the basal lamina at a lesion site was clearly discontinuous. High-voltage electron microscopy has now been used to study lesions of the efferent tubule, with the aim of understanding better their three-dimensional structure.Tissue from one maxillary gland of an infected, adult, female brine shrimp was used for HVEM study.

Chromosome polymorphism in natural populations of Anopheles quadrimaculatus Say species A and B

Genome ◽  
1988 ◽  
Vol 30 (2) ◽  
pp. 138-146 ◽  
Author(s):  
P. E. Kaiser ◽  
J. A. Seawright ◽  
B. K. Birky
Keyword(s):  
X Chromosome ◽  
Southeastern United States ◽  
Polytene Chromosomes ◽  
Natural Populations ◽  
Chromosome 3 ◽  
Chromosome Polymorphism ◽  
Chromosome 2 ◽  
Anopheles Quadrimaculatus ◽  
The Right ◽  
Maculipennis Complex

Ovarian polytene chromosomes from eight populations of Anopheles quadrimaculatus in the southeastern United States were observed for chromosomal polymorphisms. Two sibling species, species A and B, each with intraspecific inversions, were distinguished. Species A correlates with the previously published standard maps for salivary gland and ovarian nurse-cell polytene chromosomes. Species A was found at all eight collection sites, and five of these populations also contained species B. Three inversions on the right arm of chromosome 3 were observed in species A. Species B contained a fixed inversion on the X chromosome, one fixed and one floating inversion on the left arm of chromosome 2, and one fixed and one floating inversion on the right arm of chromosome 3. The fixed inversion on the X chromosome makes this the best diagnostic chromosome for distinguishing species A and B. An unusual dimorphism in the left arm of chromosome 3, found in both species A and B, contained two inversions. The heterokaryotypes, as well as two distinct homokaryotypes, were seen in all of the field populations. Intraspecific clinal variations in the frequencies of the species A inversions were noted. The Florida populations were practically devoid of inversions, the Georgia and Alabama populations contained some inversions, and the Arkansas population was mostly homozygous for two of the inversions. The phylogenetic relationships of species A and B to the Maculipennis complex (Nearctic) are discussed.Key words: Anopheles, inversion, populations, chromosome polymorphism, phylogenetics.

scholarly journals GENE CONVERSION AND TRANSFER OF GENETIC INFORMATION WITHIN THE INVERTED REGION OF INVERSION HETEROZYGOTES

Genetics ◽  
1973 ◽  
Vol 75 (1) ◽  
pp. 123-131
Author(s):  
Arthur Chovnick
Keyword(s):  
Information Transfer ◽  
Logical Consequence ◽  
Natural Populations ◽  
Inverted Region ◽  
Order Of Magnitude ◽  
Inversion Heterozygote ◽  
Gene Complexes ◽  
Reciprocal Transfer ◽  
Comparison Of The Results ◽  
Transfer Of Information

ABSTRACT Prior studies of recombination which monitor exchange events in exceedingly short intervals (i.e., separable sites within a cistron) reveal that the basic event in recombination involves a non-reciprocal transfer of information, termed conversion. As a logical consequence of the model suggested by the work in Drosophila, the present investigation examined recombination between rosy mutant alleles (ry:3-52.0) in Drosophila melanogaster in a paracentric inversion (In(3R)P18) heterozygote, which placed the rosy region approximately at the center of the inverted region. Comparison of the results of this study with experiments carried out in standard chromosome homozygotes reveals a dramatic suppression of classical crossovers between the rosy mutant alleles in the inversion heterozygote. However, conversions continue to occur for all rosy mutant alleles in all heterozygous combinations in the inversion heterozygote. Moreover, the order of magnitude of conversion frequencies seen in the inversion heterozygote does not change from that seen in the standard chromosome homozygote study. The significance of these observations with reference to the role of rearrangements as barriers of information transfer is discussed. Particular attention is directed to the elaborate inversion polymorphisms seen in natural populations, and to notions concerning their role in the evolution of adaptive gene complexes.

The status and distribution of Carex subimpressa (Cyperaceae)

1986 ◽  
Vol 64 (1) ◽  
pp. 227-232 ◽  
Author(s):  
A. A. Reznicek ◽  
P. M. Catling
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Natural Populations ◽  
Field Studies ◽  
Diagnostic Character ◽  
Wide Area ◽  
Hybrid Origin ◽  
The Status ◽  
Specific Rank ◽  
Scanning Electron

Carex subimpressa, originally described as a hybrid of C. hyalinolepsis and C. lanuginosa, has been reported over a wide area and beyond the range of C. hyalinolepis. Consequently it has been accorded specific rank. Various aspects of morphology reflected in scatter diagrams as well as intermediate stomatal structure revealed through scanning electron microscopy and sectioning support the hybrid origin as originally proposed. This is further supported by field studies of natural populations where both putative parents were invariably present. Reports from beyond the range of one or both parents are the result of misidentification. The diagnostic character combination includes sparsely pubescent perigynia 4.2–6.4 mm long, with relatively short beaks, leaves 4.5–11 mm wide, and ligules 1.8–9 mm long.

The desynaptic mutant of maize as a combined defect of synaptonemal complex and chiasma maintenance

Genome ◽  
1991 ◽  
Vol 34 (6) ◽  
pp. 879-887 ◽  
Author(s):  
M. P. Maguire ◽  
A. M. Paredes ◽  
R. W. Riess
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
Central Region ◽  
Meiotic Prophase ◽  
Heterochromatic Region ◽  
Crossing Over ◽  
Related Strain ◽  
Normal Cells ◽  
Normal Crossing ◽  
Mutant Cells

The phenotype of the desynaptic (dy) mutant of maize in microsporocytes at meiotic prophase was compared with normal microsporocytes of a closely related strain and with microsporocytes of a maize inbred line (KYS) assumed to be normal. Strikingly more univalents and open arms of bivalents were found in the mutant cells than in normal cells at diakinesis, and where there was heterozygosity for a distal knob (heterochromatic region), separation was usually equational, indicating the occurrence of normal crossing-over followed by failure of chiasma maintenance in the mutant. Differences found in the mutant by electron microscopy were a statistically significant wider dimension of the synaptonemal complex central region and also less twisting of synapsed configurations at pachytene. It is suggested that these are side-effect symptoms of a defect in the synaptonemal complex (or associated substance), which is expressed later as sporadic loss of chiasma maintenance.Key words: desynaptic, chiasma maintenance, synaptonemal complex.

Population cytogenetic studies on Simulium feuerborni Edwards (Diptera: Simuliidae) from northern Thailand

Genome ◽  
1999 ◽  
Vol 42 (1) ◽  
pp. 80-86 ◽  
Author(s):  
Chaliow Kuvangkadilok ◽  
Suwannee Phayuhasena ◽  
Visut Baimai
Keyword(s):  
Polytene Chromosomes ◽  
Natural Populations ◽  
Gene Pools ◽  
Northern Thailand ◽  
Y Chromosomes ◽  
Larval Salivary Gland ◽  
Hardy Weinberg Equilibrium ◽  
Chiang Mai Province ◽  
Chromosome I ◽  
Paracentric Inversions

A standard photographic map of Simulium feuerborni (Diptera: Simuliidae) was constructed from larval salivary gland polytene chromosomes and is described herein. Analysis of polytene chromosomes was made from wild larvae collected from the four populations at Doi Inthanon National Park, Chiang Mai Province, northern Thailand. Simulium feuerborni has three pairs of chromosomes (2n = 6) which are arranged from the longest to the shortest. Chromosome I is metacentric while chromosomes II and III are submetacentric. A total of six simple paracentric inversions have been detected in these natural populations of S. feuerborni. These inversions (IS-1, IL-1, IIL-1, IIL-2, IIIS-1, IIIL-1) occurred in all chromosome arms except for the arm IIS. Significant deviation from Hardy-Weinberg equilibrium has been observed in inversion IIIL-1 at Hui Sai Luaeng suggesting the existence of two gene pools in this population. There is no indication of sex linkage associated with an inversion sequence in these populations. Thus, the X and Y chromosomes of S. feuerborni could not be recognized in this study.Key words: Simulium, polytene chromosome map, inversion polymorphisms

scholarly journals Genetic diversity and population structure of the African catfish, Clarias gariepinus (Burchell, 1822) in Kenya: implication for conservation and aquaculture

2017 ◽  
Vol 147 (2) ◽  
Author(s):  
James E. Barasa ◽  
Sinebongo Mdyogolo ◽  
Romulus Abila ◽  
Johannes Paul Grobler ◽  
Robert A. Skilton ◽  
...  
Keyword(s):  
Population Structure ◽  
Control Region ◽  
Clarias Gariepinus ◽  
Natural Populations ◽  
Fish Farm ◽  
African Catfish ◽  
Important Species ◽  
Loop Control ◽  
D Loop ◽  
Hardy Weinberg Equilibrium

African catfish, Clarias gariepinus, is an important species in aquaculture and fisheries in Kenya. Mitochondrial D-loop control region was used to determine genetic variation and population structure in samples of C. gariepinus from 10 sites including five natural populations (Lakes Victoria (LVG), Kanyaboli (LKG), Turkana (LTA), Baringo (LBA) and Jipe (LJP), and five farms (Sangoro Aquaculture Center (SAN), Sagana Aquaculture Centre (SAG), University of Eldoret Fish Farm (UoE), Kibos Fish Farm (KIB), and Wakhungu Fish Farm (WKU)) in Kenya. Similarly, samples from eight localities (four natural populations: LVG/LKG, LTA, LBA, and four farmed: SAN, SAG, KIB, UoE) were genotyped using six microsatellite DNA loci. For the D-loop control region, samples from natural sites exhibited higher numbers of haplotypes and haplotype diversities compared to farmed samples, and 88.2% of haplotypes were private. All except LJP and LTA shared haplotypes, and the highest number of shared haplotypes (8) was detected in KIB. The 68 haplotypes we found in 268 individuals grouped into five phylogenetic clades: LVG/LKG, LTA, LBA, LJP and SAG. Haplotypes of farmed C. gariepinus mostly have haplotypes typical of LVG/LKG, and some shared haplotypes of the LBA population. Microsatellite analysis showed farmed samples have higher numbers of alleles than natural samples, but higher observed and expected heterozygosity levels were found in samples of natural populations. Fifteen pair-wise comparisons had significantly different FST values. All samples were in Hardy-Weinberg equilibrium. Samples from the eight localities grouped into four genetic clusters (LVG/LKG, LTA, LBA and SAG), indicating genetically distinct populations, which should be considered for aquaculture and conservation.

G-band position effects on meiotic synapsis and crossing over.

Genetics ◽  
1988 ◽  
Vol 118 (2) ◽  
pp. 307-317
Author(s):  
T Ashley
Keyword(s):  
Complex Formation ◽  
Synaptonemal Complex ◽  
Chromosomal Rearrangement ◽  
Chromosomal Rearrangements ◽  
Crossing Over ◽  
Position Effects ◽  
Band Position ◽  
Synaptonemal Complex Formation ◽  
Meiotic Synapsis ◽  
Nonhomologous Synapsis

Abstract An examination of synaptic data from a series of X-autosome translocations and crossover data from an extensive series of autosome-autosome translocations and autosomal inversions in mice has lead to the development of a hypothesis which predicts synaptic and recombinational behavior of chromosomal aberrations during meiosis. This hypothesis predicts that in heterozygotes for chromosomal rearrangements that meiotically align G-light chromatin with G-light chromatin lack of homology will be recognized. If homologous synapsis cannot proceed, synaptonemal complex formation will cease and there will be no physical suppression of crossing over in such rearrangements. However, if a chromosomal rearrangement aligns G-light chromatin with G-dark chromatin at the time of synapsis, lack of homology will not be recognized and synaptonemal complex formation will proceed nonhomologously through the G-dark chromatin. Crossing over will be physically suppressed in this region and this suppression of crossing over will be confined to the chromosome in which the G-light chromatin is nonhomologously synapsed with G-dark chromatin. When G-light chromatin is once again aligned with G-light chromatin, lack of homology again will be recognized and either homologous synapsis will be reinitiated (as in an inversion loop), or will cease altogether (as in some translocations). Unlike the previously described "synaptic adjustment", this nonhomologous synapsis of G-light with G-dark chromatin appears to compete with homologous synapsis during early pachynema.

Heterochromatin, the synaptonemal complex and crossing over

1984 ◽  
Vol 71 (1) ◽  
pp. 159-176 ◽  
Author(s):  
S.M. Stack
Keyword(s):  
Electron Microscopy ◽  
Lycopersicon Esculentum ◽  
Synaptonemal Complex ◽  
Electron Microscopic Examination ◽  
Differential Staining ◽  
Crossing Over ◽  
Mitotic Metaphase ◽  
Plantago Ovata ◽  
Electron Microscopic ◽  
Metaphase Chromosomes

A combined light- and electron-microscopic examination of chromosomes from two angiospermous plants, Plantago ovata and Lycopersicon esculentum, and a mammal, Mus musculus, was performed. From this investigation three observations have been made that may be relevant to the observed lack of crossing over in heterochromatin. (1) Differential staining indicates that heterochromatin represents a smaller fraction of the length of pachytene chromosomes than it represents in the length of mitotic metaphase chromosomes. Since the synaptonemal complex (SC) runs throughout the length of these pachytene chromosomes, it is under-represented in heterochromatin. Considering the evidence for a rough correlation between the length of SC and the amount of crossing over, this could result in less crossing over in heterochromatin than expected on the basis of its length in mitotic metaphase chromosomes. (2) Electron microscopy indicates that, unlike the SC in euchromatin, the SC in heterochromatin is densely ensheathed in highly compact chromatin. If crossing over occurs in the SC or even in the surrounding chromatin, the compaction of the chromatin may prevent the penetration of enzymes needed in recombination. (3) Finally, a difference in the structure of SCs in euchromatin versus heterochromatin was observed that could be associated with the lack of crossing over in heterochromatin.

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