Comparative cytogenetic variability of polytene chromosomes from salivary glands of Chironomus riparius Mg., 1804 (Diptera, Chironomidae) from two polluted biotopes in Bulgaria and Russia

The structural-functional variation of Chironomus riparius salivary gland polytene chromosomes was studied in two geographically isolated Palearctic regions, Bulgaria (village Pancharevo) and Russia (St. Petersburg). The two biotopes, where larvae were collected, were polluted with various heavy metals from anthropogenic sources. Hereditary paracentric heterozygous inversions were characteristic of the Russian population, whereas somatic paracentric or pericentric heterozygous inversions were more common in the Bulgarian one. All inversions occurred at low frequencies. Other aberrations found in the two populations included somatic deletions resulting in a pompon structure of chromosome IVG, heterozygous translocation between chromosomes IVG and IIIF, enlargement of individual disks, and the appearance of a heterozygous block close to the centromere of chromosome IVG. In addition, changes in functional activity of the nucleolus organizer and Balbiani rings (BRc/BRb) were observed. Several aberration breakpoints proved to coincide with satellites of the Alu and Hinf families.     

Genetic differentiation in theAedes atropalpus complex. II. Chromosomal divergence betweenAe. atropalpus andAe. epactius

Analysis of meiotic chromosomes from hybrids betweenAedes atropalpus andAe. epactius has revealed that the two species are fixed for alternate arrangements of four inversions: a paracentric inversion of chromosome 1, two paracentric inversions of chromosome 2, and a pericentric inversion of chromosome 3. This chromosomal heterozygosity in the interspecific hybrids has resulted in extensive meiolic chromosomal asynapsis. Dicentric bridges, acentric fragments, and chromosomal breakage were also associated with the heterozygous inversions. This disruption of meiosis was sufficient to account for the partial sterility observed in interspecific hybrids. No chromosomal polymorphisms, aberrations, or reduction in fertility was observed in parental strains of intraspecific hybrids of the two species.     

Chromosome Differentiated Populations of Cruzii: Evidence for a Third Sibling Species

Anopheles cruziiis the most common species of mosquito in Southeast Brazil and a vector of human and monkey malaria. The banding pattern of the ovarian polytene chromosomes and the frequencies of paracentric inversions of individuals from two populations were studied. A new sequence of bands on the sex chromosome, defined as form C, was disclosed. In both populations where forms A (considered as standard) and C are sympatric no heterozygotes were detected. A sequence of events that could account for the observed changes in the banding sequences of the X chromosome forms was proposed. The frequencies of 22 paracentric inversions were used to assess panmixia and the results indicated the presence of two distinct genetic pools in each population. We consider these results as evidence of another sibling species in the taxon cruzii, characterized by a distinctive form of the X chromosome and provisionally designated Anopheles cruziispecies C.     

Chromosomal localization of zein genes by in situ hybridization in Zea mays

Summary In order to localize the genes coding for zein, the major storage protein of maize endosperm, zein ¹²⁵I-mRNA and ³H-cDNA labelled at high specific activity were used for in situ hybridization on heterozygous interchanges and paracentric inversions of the KYS strain of Zea mays. The analysis of the diplotene-metaphase I microsporocytes indicated the presence of zein structural genes on the long arm of chromosomes 4 and 5, the short arm of chromosome 7 and the distal segment of the long arm of chromosome 10. The two hybridization sites on chromosomes 7 and 10 are found near opaque-2 and opaque-7 loci which are known to regulate zein synthesis. The present data are discussed in relation to results obtained by other authors using genetical mapping of zein genes.     

Chromosomal evolution of the Hawaiian Telmatogeton (Chironomidae,Diptera)

It is only in the Hawaiian Islands that species of the otherwise marine genus Telmatogeton have evolved into freshwater. An analysis of polytene chromosomes and karyotypes of two marine species and five freshwater species revealed that paracentric inversions and centric fusions were important in chromosomal evolution. The sequence of polytene chromosome bands common to most species, established as the Telmatogeton standard sequence, is found in a population of T. torrenticola from West Maui. Most species and other populations of T. torrenticola may be derived from the standard sequence by paracentric inversions. Similarities with the standard band sequence places T. japonicus (n=7) rather than T. pacificus (n=4) in the proposed phylogeny as the species closest to the marine ancestor of the freshwater species. One of three species (T. fluviatilis from Oahu, T. torrenticola from West Maui, or an undescribed species from East Maui), each with seven pairs of chromosomes is considered to be closest to the original freshwater species. T. torrenticola is a complex species in which there is an accumulation of fixed inversions and centric fusions in stepwise fashion in populations from west to east (West Maui n=7; East Maui n=6; Kohala Mountains n=5 and Mauna Kea n=4 both from the island of Hawaii). The population of T. torrenticola from Molokai has a reduced chromosome number (n=4) and fixed inversions. T. abnormis and T. hirtus, the only species which exhibit differentiated sex chromosomes, may be derived from the standard sequency by paracentric inversions. T. abnormis (n=4) has a simple XY system and T. hirtus (n=3/4) has a complex XY₁Y₂ system. Unique sequences of bands, differences in staining intensity of puffs and bands, and an inversion form the basis for the differentiation of the various Y-chromosomes in these species.     

Effect of Environmental Pollution on the Chromosomal Variability of Chironomus Riparius

Different frequencies of chromosomal alterations in salivary gland polytene chromosomes AB, CD and EF were described in larvae of Chironomus riparius (syn. Chironomus thummi) from the trace metal-polluted station of Santena on the river Banna, near Turin, and from the unpolluted station of Corio (40 Km from Turin) which was taken as a reference area. In a sample of 56 larvae from Santena, no specimen with the standard karyotype in all cells of the salivary glands was found. Different types of aberrations were found: 33 paracentric and five pericentric inversions, three deficiencies, four amplified sections and one chromatid break. Fifteen out of the 38 inversions and two amplified sections appeared to be inherited, while all the other aberrations were somatic. Most of the aberrations' breakpoints were located on both sides of the centromere regions, where constitutive heterochromatin is present. Also functional alterations were observed (mainly telomere and centromere decondensations and nine novel puffs). In a sample of 49 larvae of a population from the well-preserved area of Corio only six somatic and one inherited paracentric inversions were found. These results suggest that the strong destabilization of the genomes of C. riparius larvae from Santena could be a reaction to the activity of the toxic substances present in the polluted sediments of the river Banna. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chromosomal and genomic mutations in <Emphasis Type="Italic">Chironomus plumosus</Emphasis> (L.) (Diptera,Chironomidae) from Novozybkov raion of Bryansk oblast

The data on karyopool analysis of Chironomus plumosus from Novozybkov raion of Bryansk oblast, radioactively contaminated as a result of the Chernobyl accident, are presented. In the karyopool of this population, four types of heterozygous inversions (A1.2, B1.2, C1.2, D1.2) and a structurally small rearrangement in arm D, which is thought to be also associated with inversion, were identified. For inversions A1.2, C1.2, and structurally small rearrangement in arm D the cases of somatic mosaicism were described. The mean number of inversions per individual constituted 0.78. The number of genotypic combinations was 13. In 5% of the individuals chromosome B was identified, while 15.6% were polyploid (3n). In 1.8% of triploids somatic mosaicism for the level of polytene chromosomes was observed. Most of the larvae were characterized by partial asynapsis of the homologs in different regions of chromosome III. Specific features of the Chironomus plumosus karyopool from Novozybkov are thought to be associated with the habitation of a number of generations of this population on radioactively polluted territory.     

Chromosomal polymorphisms in the pitcher-plant mosquito,Wyeomyia smithii

A local population of the pitcher-plant mosquito, Wyeomyia smithii (Diptera: Culicidae, Culicini) in western New York State contains naturally polymorphic salivary gland chromosomes. Maps depicting the proposed standard sequence of bands along each of the three chromosomes are presented. Structural conformations of heterokaryotypes reveal ten paracentric inversions. Four inversions occur in chromosome 1, and three in each of chromosomes 2 and 3. All the inversions are small, occupying 3–17% of the length of their respective chromosomes, and all are located in the terminal 1/5 to 1/2 of a chromosome arm. Three inversions are almost adjacent on chromosome 1. On chromosome 2 one inversion lies completely within another. Three inversions on chromosome 3 partially overlap. The remaining two inversions occur alone, one on chromosome 1 and the other on chromosome 2. Another polymorphism, with no visible alteration of band sequence, produces asynapsis of all but the tip of the left arm of chromosome 1, and shows a significant change in frequency between two successive years. No inversion exhibits a significant seasonal change in frequency, though some fluctuation in frequency was noted in two cases. The rarest inversion in the population exists at a frequency below 0.01, and the two most common inversions at frequencies of 0.44 and 0.52. The average inversion heterozygosity of an individual is between 1.7 and 2.4 based on two different estimation procedures. Heterokaryotypes for several of the inversions were significantly more frequent than they should have been, given binomial expectations. Cytogenetic analysis of W. smithii was deemed particularly desirable because this species has been and continues to be the subject of extensive biometrical-genetic, ecological, and evolutionary investigation.This paper is the seventh in a series on the ecology and evolution of the pitcher-plant mosquito     

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22)

Summary Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 6. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These result suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.     

The evolution of a highly variable sex chromosome in Gehyra purpurascens (Gekkonidae)

A karyotypic survey of the gekkonid lizard Gehyra purpurascens revealed a distinctive sex chromosome system. G-banding showed that the Z Chromosome of males is derived from a tandem fusion of two acrocentric chromosomes of a presumed ancestral Gehyra with 2n=44. Through the application of G-; N- and C-banding, a total of six morphs of the W chromosome were identified. These differ by paracentric and pericentric inversions and, in one case, by a centric shift. The possible reasons for such extensive variation in the W chromosome are considered, and it is suggested that increased mutability of the W chromosome may be a causal factor. In contrast to earlier speculations, this example demonstrates that sex chromosomes can evolve without significant changes in the amount of C-band heterochromatin.     

Variation of Spontaneous Occurrence Rates of Chromosomal Aberrations in the Second Chromosomes of DROSOPHILA MELANOGASTER

After accumulating mutations by the aid of marked inversions, spontaneous occurrence rates of chromosome aberrations were estimated for 1148 chromosome lines that originated from five stem line second chromosomes of Drosophila melanogaster. In chromosome lines originating from three stem chromosomes (CH, PQ, and RT), mutations were accumulated for 7550, 7252, and 7256 chromosome generations, respectively, but no structural change was detected. For the chromosome lines that originated from the other two stem chromosomes, the situation was different: Twenty aberrations (19 paracentric inversions and 1 translocation between the second and the third chromosomes) during 45990 chromosome generations took place in the 500 chromosome lines derived from stem line chromosome (AW), and 92 aberrations (83 paracentric inversions, 6 pericentric inversions, 2 translocations between the second and the third chromosomes and 1 transposition) arose during 45006 chromosome generations in the 500 chromosome lines derived from stem line chromosome (JH). For the AW group the occurrence rate becomes 0.00043 per chromosome per generation for all aberrations and 0.00041 for inversions. For the JH group the corresponding rates are 0.00204 and 0.00198, respectively.-A non-random distribution of the breakpoint on the salivary gland chromosome was observed and the breakpoints were concentrated in the regions 26, 29, 33, and 34.-The cytoplasms and the chromosomes (other than the second chromosomes) were made approximately uniform throughout the experiments. Thus, this remarkable variability in the occurrence rate is most probably due to the differences in one or more chromosomal elements on the original five stem chromosomes. The mutable chromosomes (AW and JH) appear to carry a kind of mutator factor such as hi (Ives 1950).     

Inversion polymorphism in populations of Drosophila sulphurigaster albostrigata and Drosophila nasuta albomicans from Phuket,Thailand

Two species of the Drosophila nasuta subgroup of the Drosophila immigrans group, D. sulphurigaster albostrigata and D. nasuta albomicans were investigated in this study. Collections of both species were made from Phuket, Thailand. Both species have similar salivary chromosomes, with four autosomal arms and one sex chromosome arm, and both are highly polymorphic for paracentric inversions. D. s. albostrigata accounted for the majority of the isolines collected and exhibited the greater number of inversions. One inversion, C₁, was common to both species, indicating common ancestry.A non-random distribution of inversions was observed on the proximal end of chromosome II in both D. s. albostrigata and D. n. albomicans. An inter-collection comparison revealed that both rigid and flexible chromosomal polymorphism were operating in the two species, with a seasonal variation noted for one inversion in D. s. albostrigata. A non-random association of two inversions was observed in D. n. albomicans.Based on a comparison of the indices of crossing over, both D. s. albostrigata and D. n. albomicans were found to be more heterozygous than in previous studies, with D. n. albomicans appearing to have evolved further than D. s. albostrigata.Based on a thesis submitted for the degree of Ph. D. at the University of Queensland.     

Chromosome and nucleotide sequence differentiation in genomes of polyploid Triticum species

Summary The nature of genome change during polyploid evolution was studied by analysing selected species within the tribe Triticeae. The levels of genome changes examined included structural alterations (translocations, inversions), heterochromatinization, and nucleotide sequence change in the rDNA regions. These analyses provided data for evaluating models of genome evolution in polyploids in the genus Triticum, postulated on the basis of chromosome pairing at metaphase I in interspecies hybrids.The significance of structural chromosome alterations with respect to reduced MI chromosome pairing in interspecific hybrids was assayed by determining the incidence of heterozygosity for translocations and paracentric inversions in the A and B genomes of T. timopheevii ssp. araraticum (referred to as T. araraticum) represented by two lines, 1760 and 2541, and T. aestivum cv. Chinese Spring. Line 1760 differed from Chinese Spring by translocations in chromosomes 1A, 3A, 4A, 6A, 7A, 3B, 4B, 7B and possibly 2B. Line 2541 differed from Chinese Spring by translocations in chromosomes 3A, 6A, 6B and possibly 2B. Line 1760 also differed from Chinese Spring by paracentric inversions in arms 1AL and 4AL whereas line 2541 differed by inversions in 1BL and 4AL (not all chromosomes arms were assayed). The incidence of structural changes in the A and B genomes did not coincide with the more extensive differentiation of the B genomes relative to the A genomes as reflected by chromosome pairing studies.To assay changing degrees of heterochromatinization among species of the genus Triticum, all the diploid and polyploid species were C-banded. No general agreement was observed between the amount of heterochromatin and the ability of the respective chromosomes to pair with chromosomes of the ancestral species. Marked changes in the amount of heterochromatin were found to have occurred during the evolution of some of the polyploids.The analysis of the rDNA region provided evidence for rapid fixation of new repeated sequences at two levels, namely, among the 130 bp repeated sequences of the spacer and at the level of the repeated arrays of the 9 kb rDNA units. These occurred both within a given rDNA region and between rDNA regions on nonhomologous chromosomes. The levels of change in the rDNA regions provided good precedent for expecting extensive nucleotide sequence changes associated with differentiation of Triticum genomes and these processes are argued to be the principal cause of genome differentiation as revealed by chromosome pairing studies.     

Interspecific comparisons of polytene chromosomes in the genus Parasarcophaga (Sarcophagidae: Diptera)

A comparison of the polytene chromosomes of Parasarcophaga argyrostoma, P. ruficornis, P. misera and P. knabi, is presented. There is close resemblance in the banding patterns of the four species. Two independent paracentric inversions in chromosome arm IIR, a small paracentric inversion in chromosome arm IIIR and a pericentric inversion in chromosome V were found to be fixed as interspecific differences.     

Cytogenetic mapping of marker genes on the chromosome elements C and E of Drosophila pseudoobscura and D. subobscura

Enzyme loci, visible marker genes and -cloned DNA-sequences from a D. miranda library were mapped cytologically on the chromosome elements C and E of D. pseudoobscura and D. subobscura. New data are incorporated into the linkage maps of the two species. Homologous segments can now be localized in the polytene chromosomes with these markers. A comparison of the chromosome elements E of D. melanogaster and D. subobscura shows 12 conserved subsections which have been rearranged by paracentric inversions in the evolution of the two lineages.     

Cytogenetic characteristics of a population of Chironomus riparius Meigen 1804 (Diptera, Chironomidae) from a polluted Po river station

A population of Chironomus riparius from a Po river station near Moncalieri (a trace-metal polluted station) was studied. In this population was established a great variability of band structure of polytene chromosomes as well as paracentric heterozygous inversions, deletions, deficiencies, partial breaks, diploid chromosome fragments, and changes in functional activity and appearance of heterochromatin. In arms A through F, some bands had an increased size compared to the standard chromosomic map. Some bands appeared in a heterozygous or normal homozygous state or were amplified. In all arms, many condensed stable bands appeared in the decondensed state when compared to the standard map. Asynaptic zones in arms E and G as well as heterozygous Balbiani rings and NORs were established. Very often the 4th chromosome was almost completely heteropycnotic and looded like a pompon chromosome. For the first time in this species, a high frequency of ectopic pairings of different arms was observed. Telomeric regions involved in ectopic pairings had a granular appearance, as did some centromeres. The hypothesis is advanced that such a high frequency of structural rearrangements could be correlated with genomic distribution of specific mobile elements.     

Replication banding studies in two cyprinid fishes

The use of the in vivo 5-bromodeoxyuridine (BrdU) incorporation technique made it possible to induce highly reproducible replication bands of the RBA type in two species of the order Cypriniformes (Teleostei), Rutilus rutilus and Scardinius erythrophthalmus. This allowed unequivocal identification of each individual chromosome by its banding pattern and the preparation of species specific karyotypes. Comparison of RBA-banded karyotypes of these two closely related fish species revealed that the majority of the chromosomes could be homoeologized either directly, or by assuming paracentric or pericentric inversions.by D. Schweizer     

The polytene chromosomes of Drosophila triauraria and D. quadraria, sibling species of D. auraria.

The polytene chromosomes of Drosophila triauraria and D. quadraria, two of the sibling species of D. auraria, were examined. The polytene chromosomes of all three species exhibit very clear homology. Unlike the stock of D. auraria that we studied, D. triauraria and D. quadraria carry heterozygous paracentric inversions. In both species, 2R and 3R are the arms where these inversions are concentrated. In addition, in D. quadraria, the 3L chromosome arm is very complicated because of heterozygous inversions. The mode of inheritance of these rearrangements was studied. A homozygous strain for all chromosome arms of D. triauraria was isolated, while a homozygous strain was obtained only for the arms X, 2L, 3L, and 4 of D. quadraria. Like D. auraria, both species show a large number of inverted tandem duplications in the paired condition, even in the chromosomes of their hybrids. Small deletions were also detected, one of which, in D. triauraria, is homozygous terminal. Hypotheses are discussed concerning the relationships of the species and the existence of inverted tandem duplications.     

Cytogenetic Features of Blackfly Wilhelmia paraequina Puri (Diptera: Simuliidae) from Armenia

Three blackfly Wilhelmia paraequina populations of Armenia (rivers Debet and Megriget, channel Megri) were studied. 2n = 6: IS + IIL, IIS + IL, IIIS + IIIL. Cytological maps of polytene chromosomes were constructed. High inversion polymorphism (95.63%) was observed, with 2.6 inversions per individual. Three inversions proved to be associated with male development: Y₁ was characterized by a combination of two heterozygous inversions, IIL-3 + IIL-1, while Y₂ had another combination of heterozygous inversions, IIL-5 + IIL-3. The X chromosome had a standard homozygous IIL band pattern. The populations were shown to be similar in autosomal polymorphism. A tendency for differentiation was observed with respect to frequencies and types of sex-linked inversions: the sex determination system was Y₁X–XX in the Debet and Megriget populations and Y₂X–XX in the channel (Megri) population. On the strength of these findings, one W. paraequina morphotype was assumed to involve two cytotypes, A (Debet and Megriget populations) and B (Megri population).