Autosomal Arms Research Articles

Rec-1 loss of function increases recombination in the central gene clusters at the expense of autosomal pairing centers.

Meiotic control of crossover (CO) number and position is critical for homologous chromosome segregation and organismal fertility, recombination of parental genotypes, and the generation of novel genetic combinations. We here characterize the recombination rate landscape of a rec-1 loss of function modifier of CO position in Caenorhabditis elegans, one of the first ever modifiers discovered. By averaging CO position across hermaphrodite and male meioses and by genotyping 203 single-nucleotide variants covering about 95% of the genome, we find that the characteristic chromosomal arm-center recombination rate domain structure is lost in the loss of function rec-1 mutant. The rec-1 loss of function mutant smooths the recombination rate landscape but is insufficient to eliminate the nonuniform position of CO. Lower recombination rates in the rec-1 mutant are particularly found in the autosomal arm domains containing the pairing centers. We further find that the rec-1 mutant is of little consequence for organismal fertility and egg viability and thus for rates of autosomal nondisjunction. It nonetheless increases X chromosome nondisjunction rates and thus male appearance. Our findings question the maintenance of recombination rate heritability and genetic diversity among C. elegans natural populations, and they further suggest that manipulating genetic modifiers of CO position will help find quantitative trait loci located in low-recombining genomic regions normally refractory to discovery.

Multiple Chromosomal Polymorphism in Birch Mice of the Subtilis Group (Rodentia, Dipodoidea, <i>Sicista</i>) from Saratov Right Bank

Cytogenetic analysis (routine, G-, C-, AgNOR-chromosome banding) allowed to obtain new data on chromosomal polymorphism in the population (n = 13) of Sicista sp. 1, representative of the Sicista subtilis group from the Saratov Region, right bank of Volga River. It was shown that in the studied polymorphic population of a species from the northern part of the species' range (Voskresensky district of the Saratov region) the diploid number of chromosomes varies from 2n = 22 to 2n = 24, and the number of autosome arms from NFa = 39 to NFa = 44, and the sample includes the following 6 karyotype variants: with 2n = 24, NFa = 44; 2n = 24, NFa = 43; 2n = 23, NFa = 40; 2n = 23, NFa = 41; 2n = 22, NFa = 39; 2n = 22, NFa = 40. Based on G‑banding method, the determined intrapopulation chromosomal polymorphism in Sicista sp. 1 was defined by two chromosomal rearrangements: tandem translocation involving two biarmed autosomes No 4 and 10 and a pericentric inversion of pair No 6. In the studied sample (n = 13), a stable advantage of heterozygotes was revealed for both structural chromosomal mutations and the chromosomal polymorphism is characterized as balanced or heterozygous. The potential role of the identified polymorphism in chromosomal evolution and adaptive strategy of the species is discussed.

Tissue-specific chromatin-binding patterns of Caenorhabditis elegans heterochromatin proteins HPL-1 and HPL-2 reveal differential roles in the regulation of gene expression.

Heterochromatin is characterized by an enrichment of repetitive elements and low gene density and is often maintained in a repressed state across cell division and differentiation. The silencing is mainly regulated by repressive histone marks such as H3K9 and H3K27 methylated forms and the heterochromatin protein 1 (HP1) family. Here, we analyzed in a tissue-specific manner the binding profile of the two HP1 homologs in Caenorhabditis elegans, HPL-1 and HPL-2, at the L4 developmental stage. We identified the genome-wide binding profile of intestinal and hypodermal HPL-2 and intestinal HPL-1 and compared them with heterochromatin marks and other features. HPL-2 associated preferentially to the distal arms of autosomes and correlated positively with the methylated forms of H3K9 and H3K27. HPL-1 was also enriched in regions containing H3K9me3 and H3K27me3 but exhibited a more even distribution between autosome arms and centers. HPL-2 showed a differential tissue-specific enrichment for repetitive elements conversely with HPL-1, which exhibited a poor association. Finally, we found a significant intersection of genomic regions bound by the BLMP-1/PRDM1 transcription factor and intestinal HPL-1, suggesting a corepressive role during cell differentiation. Our study uncovers both shared and singular properties of conserved HP1 proteins, providing information about genomic binding preferences in relation to their role as heterochromatic markers.

Gerbillus dasyurus (Rodentia: Gerbillinae) Record from Hatay Province, in the South of Turkey

Wagner’s gerbil, Gerbillus dasyurus, is present in Middle East, Arabian Peninsula and marginally into eastern desert of Egypt. The only records have been taken from Kilis in Turkey. In the present study, 10 specimens were collected from three localities in the Hatay Province. These specimens were captured in rocky hills and slopes with poor soil and vegetation on blocky igneous rocks, and also in the rocky lava flow area in the north eastern part of the Hatay Province. Diploid number of chromosome, number of chromosomes and fundamental number of autosomal arms of the specimens was found as 2n = 60, NF = 70 and NFa = 66, respectively. The relative abundance of species was estimated to be 2.74. The mean of the entire baculum is 2.37 mm long, and 0.52 mm the maximum wide (n=3). Number of roots on molars: 3 (M1 and M2), 2 (M1 and M2) and, 1 M3 and M3. The tail lenght is markedly longer than the total legnth of head and body. Morphological and karyologic characters of the samples verify that the indivuduals investigated belongs to Gerbillus dasyurus. However, it is possible to show inter- and intrapopulational variations because of the differences seen in the root number of M1, the proportion of the tail, and the shape of baculum etc., through a detailed study that covers all distribution area. This record is the second record of the species from Turkey. Since no examples could be obtained in the later studies in Kilis region, which was the first record locality, the protection of the new record localities in Hatay is important for the survival of the species in Turkey.

Cytogenetic Characteristics of Gerbillus dasyurus and Meriones tristrami (Rodentia: Gerbillinae) from Kilis, Turkey: Conventional and C Banded Karyotypes

In this study, diploid chromosome number and constitutive heterochromatin distributions of chromosomes were determined in Gerbillus dasyurus and Meriones tristrami species. The diploid chromosome numbers (2n) and autosomal chromosome arms (NFa) of G. dasyurus and M. tristrami were determined as 2n=60, NFa= 68, and 2n=72, NFa= 73, respectively. It was found that there were differences in autosomal chromosomal arms (NFa) of two different gerbil species, the karyotypes of which were obtained in this study, compared to previously conducted studies in Türkiye. Heteromorphic chromosome pair (submetacentric/acrocentric) was found in the autosomal set of M. tristrami. There was an enlarged heterochromatin block on the short arm of submetacentric chromosome in heteromorphic chromosome pair.

Karyotypes and ZZ/ZW Sex Chromosome System of Endemic Squalius recurvirostris (Leuciscinae, Cyprinidae) in Turkey

In this study, detailed cytogenetic properties of the endemic Akşehir chub, Squalius recurvirostris, distributed in the basin of the Ilgın (Çavuşçu) Lake basin was investigated by applying the standard Giemsa staining, C-banding and Ag-NOR technique. Diploid chromosome number is (2n) 50. A pair of heteromorphic chromosomes was detected in the karyotype in females. However, this difference was not observed in males. Therefore, it was determined that the heteromorphic chromosome pair in females were ZZ/ZW sex chromosomes. The Z chromosome in females is large acrocentric, and the W chromosome is medium-sized submeta/subtelocentric. The number of all chromosomal arms (NF) is 90, and the fundamental number of autosomal arms (NFa) is 88 in the karyotyped of the individuals studied. Some bi-armed and acrocentric chromosomes have centromeric C-bands in the chromosome set. The slightly centromeric or pericentromeric C-bands are observed in some chromosomes, while other chromosome pairs are C-negative. In the individuals studied two active NORs were detected. Both of these NORs were hemizygous and associated with a large C-heterochromatin region. One of the NORs was detected on the entire long arm of the submetacentric chromosome pair and the other on the entire short arm of another submetacentric chromosome pair.

Karyotypic Analysis of the Clipper Barb <i>Enteromius callipterus</i> (Boulenger 1907) from Tahoss Stream, Jos Plateau, Nigeria

The chromosomes of male and female individuals of Enteromius callipterus [1] were assessed in this study with the objective of determining the diploid chromosome and karyotype. The samples were obtained from the Tahoss River, Jos Plateau, and the assessment of the chromosomes was conducted using the conventional Giemsa staining technique. The study reveals that the male individual of E. callipterus has a diploid chromosome number of 2n = 50, the fundamental number of autosomal arms (NFa) of 82, and a karyotype formula of 2n = 14M + 4m + 32t. However, none of the spreads obtained for the female individuals were either equal to or below the common diploid chromosome number of 50 known for members of the genus. The two spreads presented here were of 2n equal to 54 and 58. Although sex dimorphism is rare within the genus, the present results suggest E. callipterus show sexual dimorphism at the chromosomal level.

A Cytogenetic and Morphological Study on Nannospalax ehrenbergi in Adana (Ceyhan) Province

This study was conducted to explain the karyological analysis and morphological characteristics of blind mole rat samples collected from Ceyhan, Adana in Turkey. The chromosomes of the blind mole rat samples were stained and analysed using conventional methods. The chromosomes were defined according to centromere positions by processing photographs of metaphase cells. The karyotype of Nannospalax ehrenbergi showed 53 chromosomes (2n=53) and fundamental number of chromosomal arms NF=66 and the number of autosomal arms NFa= 62. The karyotype showed a hybrid individual. X and Y chromosomes were determined as metacentric and acrocentric, respectively. The autosomal set had 5 (+1 single homologous) pairs of metacentric/submetacentric and 20 pairs of acrocentric. Morphological studies were carried out on two male Nannospalax ehrenbergi skulls from Adana province. Lengths of three external (height, hindfoot length and weights (gr)) and 24 cranial morphological points on skulls were measured using an electronic caliper. This was the first study in which 2n=53 NF=66 population was determined from Ceyhan. This form was described as a hybrid form. The portion behind the palate (os palatinum) has no a sharply defined styloid process.

Chromosomal relationships among the native rodents (Cricetidae: Oryzomyini) of the Galápagos Islands, Ecuador

Although the Galápagos Islands are recognized for their contribution to our understanding of evolutionary theory and have received the attention of scientists for over 185 years, our understanding of the native rodents there has been minimal relative to many other groups of organisms. Much of what we knew through most of the 20th century was based solely on species descriptions. Chromosome data has been limited to only Nesoryzomys narboroughi (2n = 32, FN (number of autosomal arms) = 50) and Aegialomys galapagoensis (2n = 56; FN = 58). We present the karyotypes of the only remaining extant species in the genus, N. swarthi (2n = 56; FN = 54) and N. fernandinae (2n = 44; FN = 54). Chromosomal banding reveals that extensive rearrangement has occurred within Nesoryzomys, including Robertsonian fusion and tandem fusion events but these alone cannot account for the diverse diploid numbers found within the genus. We propose that 1) N. swarthi represents the ancestral karyotype for the genus, similar to A. galapagoensis, 2) N. swarthi and N. fernandinae share the same fundamental number, suggesting divergence by Robertsonian fusions, and 3) N. narboroughi has the most derived karyotype, based on banding morphology and low diploid number.

A Cytogenetic Study on Spermophilus Xanthoprymnus (Bennett, 1835) in Isparta Province

This study was conducted to explain the karyological characteristics of S. xanthoprymnus from Gencali in Turkey. The chromosomes of the specimens were traditionally stained and examined according to standard procedures. The chromosomes were determined according to centromere positions by examining the photographs of metaphase cells. The karyotype of S. xanthoprymnus contained 42 chromosomes (2n=42) and fundamental number of chromosomal arms NF=81 and the number of autosomal arms NFa=78. The karyotype includes four metacentric chromosomes ranging from large to small, three pairs of large and medium-sized submetacentric autosome, twelve ranging from large to medium size subtelocentric, and a pair of acrocentric autosomes. The X chromosome was determined as large subtelocentric and Y chromosome as small acrocentric. Due to there is no karyological information and geographical distribution of existentence cytotypes in Turkey, revelation of chromosomal structure in Anatolian ground squirrel populations will provide properly assessment of taxonomy of those rodents in further studies.

Comparative cytogenetics of two species of Dermanura (Chiroptera, Phyllostomidae) in Midwestern Brazil.

Dermanura Gervais, 1856 is represented by small frugivorous bats of the Stenodermatinae subfamily. The taxonomy of this group presents controversies and has been subject to changes, especially since the morphological characters evaluated have left gaps that are difficult to fill regarding good species characterization. Previous studies performed in Dermanura cinerea Gervais, 1856 found that the karyotype of this species has a diploid number of chromosomes equal to 30 and 56 autosomal arms. The objective of the present study was to describe, for the first time, the karyotypes of the species Dermanura anderseni (Osgood, 1916) and Dermanura gnoma (Handley, 1987) based on classical cytogenetic markers. For both species, the diploid number found was 2n = 30 and NFa = 56. Two pairs of chromosomes showed markings of the nucleolus organizing regions (AgNORs) in the species D. anderseni and only one pair in D. gnoma, differing from what has already been described for D. cinerea. The two species analyzed here also showed differences in the sex chromosome system, with D. gnoma showing a neo-XY type system while in D. anderseni the classic XY sexual system was observed. In both species, visualization of the constitutive heterochromatin occurred in the pericentromeric region of all chromosomes, as well as in the short arms of the subtelocentric chromosomes. The present work represents an important expansion of karyotypic information for the subfamily Stenodermatinae, bringing chromosomal features that are possible to use in the taxonomic implications of the group.

Comparative cytogenetics of two species of Dermanura (Chiroptera, Phyllostomidae) in Midwestern Brazil

Dermanura Gervais, 1856 is represented by small frugivorous bats of the Stenodermatinae subfamily. The taxonomy of this group presents controversies and has been subject to changes, especially since the morphological characters evaluated have left gaps that are difficult to fill regarding good species characterization. Previous studies performed in Dermanura cinerea Gervais, 1856 found that the karyotype of this species has a diploid number of chromosomes equal to 30 and 56 autosomal arms. The objective of the present study was to describe, for the first time, the karyotypes of the species Dermanura anderseni (Osgood, 1916) and Dermanura gnoma (Handley, 1987) based on classical cytogenetic markers. For both species, the diploid number found was 2n = 30 and NFa = 56. Two pairs of chromosomes showed markings of the nucleolus organizing regions (AgNORs) in the species D. anderseni and only one pair in D. gnoma, differing from what has already been described for D. cinerea. The two species analyzed here also showed differences in the sex chromosome system, with D. gnoma showing a neo-XY type system while in D. anderseni the classic XY sexual system was observed. In both species, visualization of the constitutive heterochromatin occurred in the pericentromeric region of all chromosomes, as well as in the short arms of the subtelocentric chromosomes. The present work represents an important expansion of karyotypic information for the subfamily Stenodermatinae, bringing chromosomal features that are possible to use in the taxonomic implications of the group.

Physical Mapping of the Anopheles (Nyssorhynchus) darlingi Genomic Scaffolds.

Simple SummaryAnopheles darlingi mosquitoes are the main vectors of malaria in the Brazilian Amazon. To assign genomic DNA sequences to chromosomes of this species, we performed fluorescence in situ hybridization of DNA probes with salivary glands polytene chromosomes. We compared the physical locations of the An. darlingi probes with homologous sequences in other Anopheles species, namely Anopheles albimanus and Anopheles gambiae. The results demonstrated that substantial genome rearrangements occurred throughout the evolutionary history of these mosquitoes. The physical mapping data can be useful for improving the structural accuracy of the An. darlingi genome assembly and for understanding the chromosomal evolution of these mosquitoes.The genome assembly of Anopheles darlingi consists of 2221 scaffolds (N50 = 115,072 bp) and has a size spanning 136.94 Mbp. This assembly represents one of the smallest genomes among Anopheles species. Anopheles darlingi genomic DNA fragments of ~37 Kb were cloned, end-sequenced, and used as probes for fluorescence in situ hybridization (FISH) with salivary gland polytene chromosomes. In total, we mapped nine DNA probes to scaffolds and autosomal arms. Comparative analysis of the An. darlingi scaffolds with homologous sequences of the Anopheles albimanus and Anopheles gambiae genomes identified chromosomal rearrangements among these species. Our results confirmed that physical mapping is a useful tool for anchoring genome assemblies to mosquito chromosomes.

C-Heterochromatin and nucleolus organizer region distribution of Myotis emarginatus (Chiroptera: Vespertilionidae) from Turkey

In this study, the banded karyotypes (C- and Ag-nucleolus organizer regions (NORs)) of Myotis emarginatus in Turkey were determined for the first time. The karyotype contained 44 chromosomes, the number of chromosomal arms (NF) was 54, and the number of autosomal arms (NFa) was 50. Slight C-heterochromatic blocks were observed in the centromeric regions of some autosome pairs, whereas the sex chromosomes were euchromatic. The Ag-NORs were detected in the short arms of a large and a medium-sized acrocentric autosome. The distribution of C-heterochromatin regions in Turkish populations of M. emarginatus is similar to those reported in some other Myotis species.

Three-dimensional Organization of Polytene Chromosomes in Somatic and Germline Tissues of Malaria Mosquitoes.

Spatial organization of chromosome territories and interactions between interphase chromosomes themselves, as well as with the nuclear periphery, play important roles in epigenetic regulation of the genome function. However, the interplay between inter-chromosomal contacts and chromosome-nuclear envelope attachments in an organism’s development is not well-understood. To address this question, we conducted microscopic analyses of the three-dimensional chromosome organization in malaria mosquitoes. We employed multi-colored oligonucleotide painting probes, spaced 1 Mb apart along the euchromatin, to quantitatively study chromosome territories in larval salivary gland cells and adult ovarian nurse cells of Anopheles gambiae, An. coluzzii, and An. merus. We found that the X chromosome territory has a significantly smaller volume and is more compact than the autosomal arm territories. The number of inter-chromosomal, and the percentage of the chromosome–nuclear envelope, contacts were conserved among the species within the same cell type. However, the percentage of chromosome regions located at the nuclear periphery was typically higher, while the number of inter-chromosomal contacts was lower, in salivary gland cells than in ovarian nurse cells. The inverse correlation was considerably stronger for the autosomes. Consistent with previous theoretical arguments, our data indicate that, at the genome-wide level, there is an inverse relationship between chromosome-nuclear envelope attachments and chromosome–chromosome interactions, which is a key feature of the cell type-specific nuclear architecture.

Genetic Variability of Three Isolated Populations of the Muya Valley Vole Alexandromys mujanensis Orlov et Kovalskaja, 1978 (Rodentia, Arvicolinae)

In the present study, on the basis of cytogenetic and molecular genetic (mtDNA control region) analysis, genetic variability of the Muya valley vole, Alexandromys mujanensis, an endemic of Buryatia and the northwest of Zabaykalsky krai, was assessed. Three isolated valley vole populations from the Muisko-Kuandinskaya and Barguzinskaya depressions, as well as the Baunt Lake valley, were examined. Polymorphism in the number of autosomal arms (NFa = 46–49) with a stable number of chromosomes (2n = 38), determined by morphological variability of four pairs of autosomes (MMUJ2, MMUJ7, MMUJ8, and MMUJ14), rather than two, as previously thought, was revealed. To date, for the Muya valley vole, ten karyotype variants have been identified. It seems likely that chromosomal rearrangements (pericentric inversions, as well as two variants of fusion of acrocentric chromosome pairs, i.e., centromeric-centromeric and centromeric-telomeric), which led to variability in autosome morphology in the populations of the Muya valley vole, are not harmful. Analysis of the mtDNA control region revealed high haplotype and nucleotide diversity for the species as a whole, while in the valley vole samples from the Dzherginsky Nature Reserve (Barguzinskaya Depression) and the Baunt lake valley, nucleotide diversity was reduced compared to the sample from the Muisko-Kuandinskaya Depression. Despite the fact that each of the studied populations has a unique composition of chromosomal rearrangements and mtDNA haplotypes, higher similarity between the populations of the Muisko-Kuandinskaya Depression and the populations of the Baunt lake valley can still be suggested.

Repression of Germline Genes in Caenorhabditis elegans Somatic Tissues by H3K9 Dimethylation of Their Promoters.

Repression of germline-promoting genes in somatic cells is critical for somatic development and function. To study how germline genes are repressed in somatic tissues, we analyzed key histone modifications in three Caenorhabditis elegans synMuv B mutants, lin-15B, lin-35, and lin-37—all of which display ectopic expression of germline genes in the soma. LIN-35 and LIN-37 are members of the conserved DREAM complex. LIN-15B has been proposed to work with the DREAM complex but has not been shown biochemically to be a member of the complex. We found that, in wild-type worms, synMuv B target genes and germline genes are enriched for the repressive histone modification dimethylation of histone H3 on lysine 9 (H3K9me2) at their promoters. Genes with H3K9me2 promoter localization are evenly distributed across the autosomes, not biased toward autosomal arms, as are the broad H3K9me2 domains. Both synMuv B targets and germline genes display a dramatic reduction of H3K9me2 promoter localization in lin-15B mutants, but much weaker reduction in lin-35 and lin-37 mutants. This difference between lin-15B and DREAM complex mutants likely represents a difference in molecular function for these synMuv B proteins. In support of the pivotal role of H3K9me2 in regulation of germline genes by LIN-15B, global loss of H3K9me2 but not H3K9me3 results in phenotypes similar to synMuv B mutants, high-temperature larval arrest, and ectopic expression of germline genes in the soma. We propose that LIN-15B-driven enrichment of H3K9me2 at promoters of germline genes contributes to repression of those genes in somatic tissues.

The Alteration of Subtelomeric DNA Methylation in Aging-Related Diseases.

The telomere is located at the end of the chromosome and consists of a non-coding, repetitive DNA sequence. As the cell divides, the length of telomere gradually decreases. A very short telomere can terminate mitosis, and thus telomere length becomes a hallmark of cellular aging. The 500 kb region of each autosomal arm terminal is the so-called subtelomeric region. Both telomere and subtelomere have high-density DNA repeats. Telomeres do not contain genes or CpG sequences, while subtelomeres contain small amounts of genes and high-density CpG sequences, and DNA methylation often occurs in subtelomeres. Previous studies have shown that aberrant methylation of subtelomeric DNA exists in many diseases, and it has a certain effect on the regulation of telomere length. In this review, we focus on the correlation between subtelomeric DNA methylation and aging-related diseases. We also summarize the relationship between subtelomeric methylation and telomere length in different diseases.

Inverted repeat structures are associated with essential and highly expressed genes on C. elegans autosome distal arms.

Complementary sequences in cellular transcripts base-pair to form double-stranded RNA (dsRNA) structures. Because transposon-derived repeats often give rise to self-complementary sequences, dsRNA structures are prevalent in eukaryotic genomes, typically occurring in gene introns and untranslated regions (UTRs). However, the regulatory impact of double-stranded structures within genes is not fully understood. We used three independent methods to define loci in Caenorhabditis elegans predicted to form dsRNA and correlated these structures with patterns of gene expression, gene essentiality, and genome organization. As previously observed, dsRNA loci are enriched on distal arms of C. elegans autosomes, where genes typically show less conservation and lower overall expression. In contrast, we find that dsRNAs are associated with essential genes on autosome arms, and dsRNA-associated genes exhibit higher-than-expected expression and histone modification patterns associated with transcriptional elongation. Genes with significant repetitive sequence content are also highly expressed, and, thus, observed gene expression trends may relate either to dsRNA structures or to repeat content. Our results raise the possibility that as-yet-undescribed mechanisms promote expression of loci that produce dsRNAs, despite their well-characterized roles in gene silencing.

Partial-arm translocations in evolution of malaria mosquitoes revealed by high-coverage physical mapping of the Anopheles atroparvus genome

BackgroundMalaria mosquitoes have had a remarkable stability in the number of chromosomes in their karyotype (2n = 6) during 100 million years of evolution. Moreover, autosomal arms were assumed to maintain their integrity even if their associations with each other changed via whole-arm translocations. Here we use high-coverage comparative physical genome mapping of three Anopheles species to test the extent of evolutionary conservation of chromosomal arms in malaria mosquitoes.ResultsIn this study, we developed a physical genome map for Anopheles atroparvus, one of the dominant malaria vectors in Europe. Using fluorescence in situ hybridization (FISH) of DNA probes with the ovarian nurse cell polytene chromosomes and synteny comparison, we anchored 56 genomic scaffolds to the An. atroparvus chromosomes. The obtained physical map represents 89.6% of the An. atroparvus genome. This genome has the second highest mapping coverage among Anophelinae assemblies after An. albimanus, which has 98.2% of the genome assigned to its chromosomes. A comparison of the An. atroparvus, An. albimanus, and An. gambiae genomes identified partial-arm translocations between the autosomal arms that break down the integrity of chromosome elements in evolution affecting the structure of the genetic material in the pericentromeric regions. Unlike An. atroparvus and An. albimanus, all chromosome elements of An. gambiae are fully syntenic with chromosome elements of the putative ancestral Anopheles karyotype. We also detected nonrandom distribution of large conserved synteny blocks and confirmed a higher rate of inversion fixation in the X chromosome compared with autosomes.ConclusionsOur study demonstrates the power of physical mapping for understanding the genome evolution in malaria mosquitoes. The results indicate that syntenic relationships among chromosome elements of Anopheles species have not been fully preserved because of multiple partial-arm translocations.