Haploid Chromosome Complement Research Articles

Establishment and partial characterisation of a new cell line derived from adult tissues of the tsetse fly Glossina morsitans morsitans

BackgroundInsect cell lines play a vital role in many aspects of research on disease vectors and agricultural pests. The tsetse fly Glossina morsitans morsitans is an important vector of salivarian trypanosomes in sub-Saharan Africa and, as such, is a major constraint on human health and agricultural development in the region.MethodsHere, we report establishment and partial characterisation of a cell line, GMA/LULS61, derived from tissues of adult female G. m. morsitans. GMA/LULS61 cells, grown at 28 °C in L-15 (Leibovitz) medium supplemented with foetal bovine serum and tryptose phosphate broth, have been taken through 23 passages to date and can be split 1:1 at 2-week intervals. Karyotyping at passage 17 revealed a predominantly haploid chromosome complement. Species origin and absence of contaminating bacteria were confirmed by PCR amplification and sequencing of fragments of the COI gene and pan-bacterial 16S rRNA gene respectively. However, PCR screening of RNA extracted from GMA/LULS61 cells confirmed presence of the recently described Glossina morsitans morsitans iflavirus and Glossina morsitans morsitans negevirus, but absence of Glossina pallipides salivary gland hypertrophy virus. GMA/LULS61 cells supported infection and growth of 6/7 different insect-derived strains of the intracellular bacterial symbiont Wolbachia.ConclusionsThe GMA/LULS61 cell line has potential for application in a variety of studies investigating the biology of G. m. morsitans and its associated pathogenic and symbiotic microorganisms.Graphical

A Karyological Study of Tenualosa Ilisha (Hamilton, 1822) From the Confluence of Padma and Meghna River of Bangladesh

Tenualosa ilisha (Hamilton, 1822), commonly known as Hilsha shad is a valuable and highly acceptable species in terms of their high flavored properties. Hilsha shad has striking morpho-genetical adaptation to heterogeneous habitats across their migratory routes. Cytogenetic analysis demonstrates the changes in chromosomes. But none was focused on the cytogenetic analysis of T. ilisha in Bangladesh. T. ilisha was found to possess 2n = 42 number of chromosomes along with a karyotype formula: 1M + 31m + 8sm + 2st using giemsa staining technique. The results demonstrated ‘diffuse type of interphase nuclei, co-existence of continuous type and interstitial type of prophase chromosomes respectively. No heteromorphic sex chromosomes were determined cytologically. The presence of diverse types of chromosomes based on centromeric position, gradual decrease in total haploid chromosome complement, mean centromeric asymmetry, coefficient of variation of chromosome length and Stebbins’s classification highlighted its asymmetry in karyotype with advance nature. Therefore, the elemental karyological data will offer information for the proper identification, cytotaxonomical classification, expanding productivity and preservation of genetic resources ofT. ilisha. Bangladesh J. Zool. 49 (2): 243-255, 2021

Transposons played a major role in the diversification between the closely related almond and peach genomes: results from the almond genome sequence.

SummaryWe sequenced the genome of the highly heterozygous almond Prunus dulcis cv. Texas combining short‐ and long‐read sequencing. We obtained a genome assembly totaling 227.6 Mb of the estimated almond genome size of 238 Mb, of which 91% is anchored to eight pseudomolecules corresponding to its haploid chromosome complement, and annotated 27 969 protein‐coding genes and 6747 non‐coding transcripts. By phylogenomic comparison with the genomes of 16 additional close and distant species we estimated that almond and peach (Prunus persica) diverged around 5.88 million years ago. These two genomes are highly syntenic and show a high degree of sequence conservation (20 nucleotide substitutions per kb). However, they also exhibit a high number of presence/absence variants, many attributable to the movement of transposable elements (TEs). Transposable elements have generated an important number of presence/absence variants between almond and peach, and we show that the recent history of TE movement seems markedly different between them. Transposable elements may also be at the origin of important phenotypic differences between both species, and in particular for the sweet kernel phenotype, a key agronomic and domestication character for almond. Here we show that in sweet almond cultivars, highly methylated TE insertions surround a gene involved in the biosynthesis of amygdalin, whose reduced expression has been correlated with the sweet almond phenotype. Altogether, our results suggest a key role of TEs in the recent history and diversification of almond and its close relative peach.

Meiotic chromosome behavior of the male-fertile allotriploid lily cultivar 'Cocossa'.

Cytological observations of microsporogenesis in the allotriploid lily cultivar 'Cocossa' showed that viable pollen production could be attributed mainly to disoriented spindles, abnormal cytokinesis, and cytomixis during male meiosis. To identify the reasons why the allotriploid lily cultivar 'Cocossa' can produce aneuploid and euploid functional male gametes and can be used as the paternal parent in lily introgression breeding, we performed a detailed investigation of microsporogenesis using the conventional cytological methods. The allotriploid not only produced single pollen grains with variable sizes but also produced adherent pollen grains. Pollen viability was estimated at 50.1% based on staining and 30.8% based on germination. Based on the chromosomal analysis of BC2 plants derived from Oriental cultivars (♀) crossed with the OOT cultivar 'Cocossa' (♂), it was concluded that the objective allotriploid contributed haploid (x), diploid (2x), and aneuploid chromosome complements. Common meiotic abnormalities were observed, indicating the high genetic imbalance of this allotriploid. In addition to normally oriented metaphase II spindles (linear and perpendicular), abnormal spindles, such as parallel, tripolar, fused, and multiple spindles, accounted for 6.21, 6.41, 14.27, and 1.17%, respectively. Tripolar and fused spindles resulted in the production of triads and dyads, which contributed to unreduced pollen production. Some microsporocytes exhibited complete or partial absence of cytokinesis, which led to relatively high frequencies of monads, dyads, and triads. Furthermore, the phenomenon of cytomixis during microsporogenesis occurred mainly in the first meiotic prophase and early development of pollen grains, which we assume is a possible cause of unreduced gamete generation. Our study offers a new resource for lily introgression breeding.

Oat Doubled Haploids Following Maize Pollination.

Doubled haploids (DHs) are an important tool for the accelerated production of new crop varieties. In oat, DHs were first produced by pollinating oat florets with maize pollen. The resultant embryos spontaneously eliminate the maize chromosomes leaving a haploid complement of oat chromosomes. These embryos can be cultured in vitro using the "embryo rescue" technique to produce haploid plants whose chromosome number can be doubled with colchicine to produce homozygous DH oat plants.

Flow cytometric analysis of DNA content for four commercially important crabs in China

The genome size (C-value) of an organism is referring to the DNA content of its non-replicated haploid chromosome complement, generally deduced from measuring somatic diploid nuclei. We presented genome size (C-value) data obtained by flow cytometry for four commercially important crabs (Portunus trituberculatus, Charybdis japonica, Scylla paramamosain, and Eriocheir sinensis) common in the coast of China. Gallus domesticus (2C=2.5 pg ) was used as the internal standard. The results showed that the C-value for P. trituberculatus, C. japonica, S. paramamosain, and E. sinensis were (2.31 +/- 0.01) pg, (2.33 +/- 0.03) pg, (1.64 +/- 0.02) pg, and (2.29 +/- 0.03) pg, respectively. The C-value of P. trituberculatus, C. japonica and S. paramamosain were reported for the first time. The data represented by the four species indicated that they had lower DNA contents than average DNA values in crustaceans ((4.99 +/- 0.48) pg), and three of the four values were very similar if not identical. The results provide useful data for future studies in the fields of biodiversity, species conservation, and phylogeny of these commercial crabs. They will also be helpful in instructing the hybridization breeding program and estimating the cost of the whole genome sequencing project.

Karyotype study on 15 populations of Eremostachys laciniata Bunge in Iran

A karyotype study was performed on 15 populations of Eremostachys laciniata Bunge from Iran in order to quantify the extent of cytological variation for use in breeding programmes. Ten mitotic root tip cells at the metaphase stage were prepared from each population by the squash method. The chromosomes of suitable mitotic cells were counted and various parameters, including long and short arm lengths, chromosome lengths, total length of the haploid chromosome complement, arm ratios, and the centromeric index, were measured. All 15 populations were diploid with 2n = 2x = 22 and were differentiated by their karyotypic parameters. All 15 E. laciniata populations occupied Class 1A of Stebbins’ karyotype classification, indicating the presence of a primitive symmetrical karyotype. The size of the mitotic chromosomes was medium, and mean chromosome lengths ranged from 3.84 to 4.77 μm. The shortest chromosome lengths were observed in the Ajabshir population and the longest in the Heydarabad population. The Heydarabad population also had the longest total chromosome length and the Ajabshir population had the shortest total chromosome length. The centromeric indices of the chromosome complements varied from 39.3% to 43.7%. Metacentric chromosomes were the most common in all populations, whereas submetacentric chromosomes were rare. The A1 index varied from 0.215 (Areshtanab) to 0.337 (Til). The A2 index ranged from 0.116 (Til) to 0.143 (Kaleybar), and the karyotype asymmetry index varied between 0.051 and 0.097. The results of a principal component analysis (PCA) showed that the main elements of the first three main principal components accounted for 97% of the total variance. Cluster analysis by Ward’s method indicated that all 15 populations could be classified into three clusters. Finally, the results of the karyotypic parameters showed that the Til, Heydarabad, and Marand populations had higher levels of karyotypic heterogeneity and may be useful when developing breeding programmes.

Recurrent Hydatidiform Mole

INTRODUCTION: Hydatidiform mole is an abnormal pregnancy characterized by proliferation of trophoblastic tissue and hydropic placental villi. The incidence is approximately 0.1% of pregnancies. We present a case involving a patient with four molar pregnancies and address management strategies to improve future pregnancy outcomes. CASE REPORT: A 23-year-old woman, gravida 5 para 0040, presented for obstetric care at 9 weeks of gestation. Her obstetric history included three histologically proven complete molar pregnancies and one spontaneous abortion. Initial ultrasonography demonstrated a snowstorm appearance and no fetal pole. The patient underwent suction dilation and curettage. Pathology confirmed complete hydatidiform mole. Serial quantitative human chorionic gonadotropin levels were followed to resolution. The patient and her partner had normal karyotypes. DISCUSSION: The cytogenetics of molar pregnancy may shed light on management options. In complete hydatidiform mole, the genetic material is paternal in origin resulting from fertilization of an oocyte without maternal genetic information. Recurrent complete molar pregnancy may indicate abnormal maternal oocyte formation. In vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis is reasonable under such circumstances. If maternal oocytes consistently do not contain a haploid chromosome complement, oocyte or embryo donation may be required for a successful pregnancy. CONCLUSION: In the setting of recurrent molar pregnancy, IVF with ICSI and preimplantation genetic diagnosis may be offered. Other management options would include oocyte or embryo donation.

Insights into the Dekkera bruxellensis Genomic Landscape: Comparative Genomics Reveals Variations in Ploidy and Nutrient Utilisation Potential amongst Wine Isolates

The yeast Dekkera bruxellensis is a major contaminant of industrial fermentations, such as those used for the production of biofuel and wine, where it outlasts and, under some conditions, outcompetes the major industrial yeast Saccharomyces cerevisiae. In order to investigate the level of inter-strain variation that is present within this economically important species, the genomes of four diverse D. bruxellensis isolates were compared. While each of the four strains was shown to contain a core diploid genome, which is clearly sufficient for survival, two of the four isolates have a third haploid complement of chromosomes. The sequences of these additional haploid genomes were both highly divergent from those comprising the diploid core and divergent between the two triploid strains. Similar to examples in the Saccharomyces spp. clade, where some allotriploids have arisen on the basis of enhanced ability to survive a range of environmental conditions, it is likely these strains are products of two independent hybridisation events that may have involved multiple species or distinct sub-species of Dekkera. Interestingly these triploid strains represent the vast majority (92%) of isolates from across the Australian wine industry, suggesting that the additional set of chromosomes may confer a selective advantage in winery environments that has resulted in these hybrid strains all-but replacing their diploid counterparts in Australian winery settings. In addition to the apparent inter-specific hybridisation events, chromosomal aberrations such as strain-specific insertions and deletions and loss-of-heterozygosity by gene conversion were also commonplace. While these events are likely to have affected many phenotypes across these strains, we have been able to link a specific deletion to the inability to utilise nitrate by some strains of D. bruxellensis, a phenotype that may have direct impacts in the ability for these strains to compete with S. cerevisiae.

Whole­genome triplication and species radiation in the southern African tribe Heliophileae (Brassicaceae)

AbstractThe unigeneric tribe Heliophileae includes ca. 90 Heliophila species, all endemic to southern Africa. The tribe is morphologically the most diverse Brassicaceae lineage in every aspect of habit, foliage, flower and fruit morphology. Despite this diversity, virtually nothing is known about its origin and genome evolution. Here we present the first in­depth information on chromosome numbers, rDNA in situ localization, genome structure, and phylogenetic relationship within Heliophileae. Chromosome numbers determined in 27 Heliophila species range from 2n = 16 to 2n = ca. 88, but 2n = 20 and 22 prevail in 77% of the examined species. Chromosome­number variation largely follows three major lineages (A, B, and C) resolved in the ITS phylogeny. Clade A species mostly have a chromosome number of 2n = 20, whereas 2n = 22 is the dominant number in clade C (2n = 16 and 22 were counted in two diploid species of clade B). The number and position of 5S and 45S rDNA loci vary between species and cannot be employed as phylogenetically informative characters. Seven species with different chromosome number and from the three ITS clades were analyzed by comparative chromosome painting. In all species analyzed, 90% of painting probes unveiled three homeologous chromosome regions in Heliophila haploid chromosome complements. These results suggest that all Heliophila species, and probably the entire tribe Heliophileae, experienced a whole­genome triplication (WGT) event. We hypothesize that the mesohexaploid ancestor arose through hybridization between genomes resembling the Ancestral Crucifer Karyotype with n = 8. The WGT has been followed by species­specific chromosome rearrangements (dip­loidization) resulting in descending dysploidy towards extant quasi­diploid genomes. More recent neopolyploidization events are reflected by higher chromosome numbers (2n = 32­88). The WGT might have contributed to diversification and species radiation in Heliophileae. To our knowledge, this is the first study to document polyploidy as a potential major mechanism for the radiation of a Cape plant lineage.

Synthesis and cytological analyses of hybrids between hexaploid wheat, with and without Ph1, and diploid wheatgrass

The usefulness of wide hybridization in genetic enhancement of crop plants like wheat, Triticum aestivum L. (2n = 6x = 42; AABBDD genomes), is well documented. Diploid wheatgrass, Lophopyrum elongatum (Host) A. Love (2n = 2x = 14; EE genome), is a source of several desirable traits including Fusarium head blight resistance. The objective of this study was to report on the synthesis and cytological analyses of wheat × wheatgrass hybrids and highlight homoeologous pairing involving the wheat and wheatgrass chromosomes. We hybridized wheatgrass with two important, crossable cultivars, ‘Chinese Spring,’ and ‘Fukohokomugi,’ of bread wheat and produced 11 tetraploid (2n = 4x = 28; ABDE) and two pentaploid (2n = 5x = 28; ABDEE) hybrids. To help promote homoeologous pairing and hence genetic recombination between the wheat and grass chromosomes, we also used the Chinese Spring mutant ph1bph1b. Using molecular markers, we readily detected intergeneric hybrids without Ph1. The hybrids without Ph1 showed multivalent formation involving wheat and grass chromosomes. However, the lack of Ph1 produced a much higher homoeologous pairing in the haploid chromosome complement in the CS ph1bph1b × wheatgrass hybrids than in the disomic complement of CS ph1bph1b. The pentaploid hybrids resulted from the fusion of a normal 21-chromsome gamete of the wheat parent with an unreduced, 14-chromsome gamete of diploid wheatgrass. These hybrids showed a remarkable degree of Ph1-enforced preferential pairing among the homologous wheatgrass chromosomes. Varying degrees of homoeologous pairing in various hybrids were detected that could facilitate alien gene transfer into wheat.

Comparative Karyotype Investigations in the European Crayfish Astacus astacus and A. leptodactylus (Decapoda, Astacidae)

AbstractThis study reports on the chromosome number and karyological characteristics of the endangered species of European crayfish, Astacus astacus and A. leptodactylus (Decapoda, Astacidae), both native to Croatian freshwater habitats. The karyotype of A. astacus and A. leptodactylus consists of 2n = 176 and 2n = 180 chromosomes, respectively. The haploid chromosome complement of A. astacus consists of 52 metacentric, 35 metacentric-submetacentric, and 1 acrocentric chromosomes. Fluorochrome staining with 4,6-diamino-2-phenylindole (DAPI) has revealed that the karyotypes of A. astacus and A. leptodactylus are characterized by large heterochromatic blocks located at centromeric and intercalary positions on the chromosomes. Interstitial heterochromatic blocks were more frequent in A. astacus than in A. leptodactylus. In both species pairing of chromosomes in meiosis was regular with the majority of bivalents in a ring- and a dumbbell-form. Fluorescence in situ hybridization (FISH) has revealed that two 45S rDNA loci were present in the investigated species. In A. astacus one of the two 45S rDNA-bearing chromosome pairs was highly heteromorphic, exhibiting a three-fold size difference between 45S rDNA sites on homologous chromosomes. Such a size difference was significantly less pronounced in A. leptodactylus. The karyotype differences between A. astacus and A. leptodactylus suggest changes in chromosome number as well as position of repetitive DNAs have played a role in the karyotype evolution of the species of Astacus.

Mitotic and meiotic chromosomes of the variable hare (Lepus timidus L.), the common hare (Lepus europaeus Pall.) and their hybrids.

Mitotic and meiotic chromosome studies in the variable hare (Lepus timidus L.), the common hare (Lepus europaeus Pall.) and their hybrids have shown a diploid chromosome number of 48. No differences in chromosome structure could be established between the two species. There was a normal meiotic behaviour of the chromosomes in the male hybrids with the formation of secondary spermatocytes with a normal haploid chromosome complement. The hybrids appeared to have a normal fertility and the reproductive barrier existing between the two species was apparently not built up by sterility factors.

Anguina paludicola sp. n. (Tylenchida: Anguinidae): The nematode associated with Rathayibacter toxicus infection in Polypogon monspeliensis and Lachnagrostis filiformis in Australia

Anguina paludicola sp. n. is described from Polypogon monspeliensis from southeastern South Australia and Lachnagrostis filiformis from northern New South Wales, following an examination of nematode populations by allozyme electrophoresis and morphological analysis. Genetic differences were consistent with those expected from conspecific allopatric populations and were based on geography rather than host. Morphological differences between nematodes from P. monspeliensis and L. filiformis were inconsistent and varied between different gall types on the same host plant. The new species is characterised by adults with irregular and variable tail termini, which appear lobed; females may have a process of vestigial ovary extending from the post uterine sac towards the tail; males are dorsally curved with a single reflexed testis; and the haploid chromosome complement is n=18.

Regeneration of fertile green plants from oat isolated microspore culture

Regeneration of fertile green plants from isolated oat microspores is reported for the first time. Factors critical for microspore growth and regeneration include cold pre-treatment, pH of culture medium and the use of conditioned culture medium. It was found that cold pre-treatment at 4 degrees C in the dark for a minimum of 6 weeks was necessary to consistently achieve microspore growth into multicellular structures (MCS). Longer pre-treatments of up to 9 weeks were tested and found to be positively correlated with the number of MCS produced. Microspore culture medium with pH 8.0 produced significantly more MCS larger than eight cells in size than media with pH 5.8. The use of medium conditioned by actively growing barley microspores significantly increased the numbers of MCS larger than eight cells in size compared to non-conditioned media. Plants were regenerated only from cultures using conditioned medium. A total of 2 green plants and 15 albinos were regenerated. Of the green plants, one had the haploid chromosome complement (n = 3x = 21) and the other had the parental hexaploid chromosome complement (2n = 6x = 42) which may be due to spontaneous chromosome doubling. The hexaploid plant set seed naturally and the haploid plant set seed after its chromosome complement was doubled with colchicine.

Karyotype differentiation among Spondias species and the putative hybrid Umbu-cajá (Anacardiaceae)

Spondias L. comprises at least nine Neotropical species, including the widely cultivated S. monbim and S. tuberosa. Umbu-caja, a putative hybrid between these two species, is also grown. In this paper, the karyotypes of five Spondias species and Umbu-caja were analysed for evidence of this hybridization. Chromosome banding with chromomycin A3 and the distribution of 5S and 45S rDNA sites were used to characterize the plants, also genomic in situ hybridization using nuclear DNA from both putative parents and the hybrid as probes. All material presented the same chromosome number (2n = 32) and morphology, but differed in the number and distribution of bands. Spondias monbim and S. tuberosa, the supposed relatives of Umbu-caja, displayed similar banding patterns, with five to six chromosome pairs having terminal bands, whereas Umbu-caja exhibited bands on both members of nine chromosome pairs. The three other species, S. venulosa, S. cytherea and S. purpurea, showed less closely related karyotypes, with bands in 12–18 chromosome pairs. In situ hybridization with 5S and 45S rDNA probes revealed one site of each probe per haploid chromosome complement in all material. However, in S. tuberosa, the location of 5S rDNA was different from the other species and found no counterpart in Umbu-caja. Several tests with total DNA from S. mombin and S. tuberosa against metaphase chromosomes of Umbu-caja failed to differentiate the individual genomes in the hybrid. From the chromosome banding and the distribution of rDNA sites, as well as from the genomic in situ hybridization, it seems clear that Umbu-caja is related closely to S. monbim and S. tuberosa, but it is karyotypically homozygous and distinct from theses other species. Karyotypically, the three other investigated species were related less closely to Umbu-caja. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 541–547.

Ancestral chromosomal blocks are triplicated in Brassiceae species with varying chromosome number and genome size.

The paleopolyploid character of genomes of the economically important genus Brassica and closely related species (tribe Brassiceae) is still fairly controversial. Here, we report on the comparative painting analysis of block F of the crucifer Ancestral Karyotype (AK; n = 8), consisting of 24 conserved genomic blocks, in 10 species traditionally treated as members of the tribe Brassiceae. Three homeologous copies of block F were identified per haploid chromosome complement in Brassiceae species with 2n = 14, 18, 20, 32, and 36. In high-polyploid (n >or= 30) species Crambe maritima (2n = 60), Crambe cordifolia (2n = 120), and Vella pseudocytisus (2n = 68), six, 12, and six copies of the analyzed block have been revealed, respectively. Homeologous regions resembled the ancestral structure of block F within the AK or were altered by inversions and/or translocations. In two species of the subtribe Zillineae, two of the three homeologous regions were combined via a reciprocal translocation onto one chromosome. Altogether, these findings provide compelling evidence of an ancient hexaploidization event and corresponding whole-genome triplication shared by the tribe Brassiceae. No direct relationship between chromosome number and genome size variation (1.2-2.5 pg/2C) has been found in Brassiceae species with 2n = 14 to 36. Only two homeologous copies of block F suggest a whole-genome duplication but not the triplication event in Orychophragmus violaceus (2n = 24), and confirm a phylogenetic position of this species outside the tribe Brassiceae. Chromosome duplication detected in Orychophragmus as well as chromosome rearrangements shared by Zillineae species demonstrate the usefulness of comparative cytogenetics for elucidation of phylogenetic relationships.

First report of meiotic chromosome number and karyotype analysis of an accession of Trigonella balansae (Leguminosae)

This study represents the first report of the number of meiotic chromosomes and morphology of the mitotic chromosomes of Trigonella balansae. The haploid complement of chromosomes of T. balansae consists of eight chromosomes (2n = 16). Of these, only the satellited chromosome and possibly a subtelocentric chromosome are identifiable. The remaining six chromosomes of each haploid chromosome complement cannot be reliably identified using arm ratio or relative length measurements.

Nuclear DNA amounts in angiosperms: progress, problems and prospects.

The nuclear DNA amount in an unreplicated haploid chromosome complement (1C-value) is a key diversity character with many uses. Angiosperm C-values have been listed for reference purposes since 1976, and pooled in an electronic database since 1997 (http://www.kew.org/cval/homepage). Such lists are cited frequently and provide data for many comparative studies. The last compilation was published in 2000, so a further supplementary list is timely to monitor progress against targets set at the first plant genome size workshop in 1997 and to facilitate new goal setting. The present work lists DNA C-values for 804 species including first values for 628 species from 88 original sources, not included in any previous compilation, plus additional values for 176 species included in a previous compilation. 1998-2002 saw striking progress in our knowledge of angiosperm C-values. At least 1700 first values for species were measured (the most in any five-year period) and familial representation rose from 30 % to 50 %. The loss of many densitometers used to measure DNA C-values proved less serious than feared, owing to the development of relatively inexpensive flow cytometers and computer-based image analysis systems. New uses of the term genome (e.g. in 'complete' genome sequencing) can cause confusion. The Arabidopsis Genome Initiative C-value for Arabidopsis thaliana (125 Mb) was a gross underestimate, and an exact C-value based on genome sequencing alone is unlikely to be obtained soon for any angiosperm. Lack of this expected benchmark poses a quandary as to what to use as the basal calibration standard for angiosperms. The next decade offers exciting prospects for angiosperm genome size research. The database (http://www.kew.org/cval/homepage) should become sufficiently representative of the global flora to answer most questions without needing new estimations. DNA amount variation will remain a key interest as an integrated strand of holistic genomics.

An Alu-mediated 31.5-kb deletion as the cause of factor XI deficiency in 2 unrelated patients

AbstractFactor XI deficiency (MIM 264900) is an autosomal bleeding disorder of variable severity. Inheritance is not completely recessive as heterozygotes may display a distinct, if mild, bleeding tendency. Recent studies have shown the causative mutations of factor XI deficiency, outside the Ashkenazi Jewish population, to be highly heterogeneous. We studied 39 consecutively referred patients with factor XI deficiency to identify the molecular defect. Conventional mutation screening failed to identify a causative mutation in 4 of the 39 patients. Epstein-Barr virus (EBV)–transformed cells from these 4 patients were converted from a diploid to haploid chromosome complement. Subsequent analysis showed that 2 of the patients had a large deletion, which was masked in the heterozygous state by the presence of a normal allele. We report here the first confirmed whole gene deletion as the causative mutation of factor XI deficiency, the result of unequal homologous recombination between flanking Alu repeat sequences.