Amount Of Repetitive DNA Research Articles

Diatom abundance in the polar oceans is predicted by genome size.

A principal goal in ecology is to identify the determinants of species abundances in nature. Body size has emerged as a fundamental and repeatable predictor of abundance, with smaller organisms occurring in greater numbers than larger ones. A biogeographic component, known as Bergmann's rule, describes the preponderance, across taxonomic groups, of larger-bodied organisms in colder areas. Although undeniably important, the extent to which body size is the key trait underlying these patterns is unclear. We explored these questions in diatoms, unicellular algae of global importance for their roles in carbon fixation and energy flow through marine food webs. Using a phylogenomic dataset from a single lineage with worldwide distribution, we found that body size (cell volume) was strongly correlated with genome size, which varied by 50-fold across species and was driven by differences in the amount of repetitive DNA. However, directional models identified temperature and genome size, not cell size, as having the greatest influence on maximum population growth rate. A global metabarcoding dataset further identified genome size as a strong predictor of species abundance in the ocean, but only in colder regions at high and low latitudes where diatoms with large genomes dominated, a pattern consistent with Bergmann's rule. Although species abundances are shaped by myriad interacting abiotic and biotic factors, genome size alone was a remarkably strong predictor of abundance. Taken together, these results highlight the cascading cellular and ecological consequences of macroevolutionary changes in an emergent trait, genome size, one of the most fundamental and irreducible properties of an organism.

Assessment of Iranian endemic Artemisia khorassanica: karyological, genome size, and gene expressions involved in artemisinin production.

The species of Artemisia, one of the largest genera of the family Asteraceae, are frequently utilized for the treatment of diseases such as malaria, hepatitis, cancer, inflammation, and infections by fungi, bacteria, and viruses. Karyological studies were performed on 18 Artemisia khorassanica populations: eleven were diploid (2n = 18) and seven were tetraploid (2n = 36). The mean chromosome lengths were 3.61 and 3.84 µm for diploids and tetraploids, respectively. Two chromosome types ("m", "sm") formed karyotype formulas "18m" for diploids and "36m" and "34m + 2sm" for tetraploids. The mean 2C DNA contents were 5.91 and 11.53 pg in diploids and tetraploids, respectively. The transcription levels of key genes involved in artemisinin production were compared in diploid (B, D, H) and tetraploid (O, P, R) A. khorassanica relative to A. annua as a standard species. No artemisinin content was detected in diploid and tetraploid A. khorassanica populations. No significant diefrences were detected between diploids and tetraploids in terms of DXR , HMGR, FDS, and ADS gene expression. This implies that most of the genomic amplification likely occurs in the amount of repetitive DNA and not in unique sequences. The DBR2 gene was expressed in the diploid A. khorassanica in a low amount but silenced in the autotetraploid A. khorassanica.

Genus-Wide Screening Reveals Four Distinct Types of Structural Plastid Genome Organization in Pelargonium (Geraniaceae).

Geraniaceae are known for their unusual plastid genomes (plastomes), with the genus Pelargonium being most conspicuous with regard to plastome size and gene organization as judged by the sequenced plastomes of P. x hortorum and P. alternans. However, the hybrid origin of P. x hortorum and the uncertain phylogenetic position of P. alternans obscure the events that led to these extraordinary plastomes. Here, we examine all plastid reconfiguration hotspots for 60 Pelargonium species across all subgenera using a PCR and sequencing approach. Our reconstruction of the rearrangement history revealed four distinct plastome types. The ancestral plastome configuration in the two subgenera Magnipetala and Pelargonium is consistent with that of the P. alternans plastome, whereas that of the subgenus Parvulipetala deviates from this organization by one synapomorphic inversion in the trnNGUU–ndhF region. The plastome of P. x hortorum resembles those of one group of the subgenus Paucisignata, but differs from a second group by another inversion in the psaI–psaJ region. The number of microstructural changes and amount of repetitive DNA are generally elevated in all inverted regions. Nucleotide substitution rates correlate positively with the number of indels in all regions across the different subgenera. We also observed lineage- and species-specific changes in the gene content, including gene duplications and fragmentations. For example, the plastid rbcL–psaI region of Pelargonium contains a highly variable accD-like region. Our results suggest alternative evolutionary paths under possibly changing modes of plastid transmission and indicate the non-functionalization of the plastid accD gene in Pelargonium.

Analysis of the giant genomes of Fritillaria (Liliaceae) indicates that a lack of DNA removal characterizes extreme expansions in genome size.

Summary Plants exhibit an extraordinary range of genome sizes, varying by > 2000‐fold between the smallest and largest recorded values. In the absence of polyploidy, changes in the amount of repetitive DNA (transposable elements and tandem repeats) are primarily responsible for genome size differences between species. However, there is ongoing debate regarding the relative importance of amplification of repetitive DNA versus its deletion in governing genome size.Using data from 454 sequencing, we analysed the most repetitive fraction of some of the largest known genomes for diploid plant species, from members of Fritillaria.We revealed that genomic expansion has not resulted from the recent massive amplification of just a handful of repeat families, as shown in species with smaller genomes. Instead, the bulk of these immense genomes is composed of highly heterogeneous, relatively low‐abundance repeat‐derived DNA, supporting a scenario where amplified repeats continually accumulate due to infrequent DNA removal.Our results indicate that a lack of deletion and low turnover of repetitive DNA are major contributors to the evolution of extremely large genomes and show that their size cannot simply be accounted for by the activity of a small number of high‐abundance repeat families.

Karyotype variability in tropical maize sister inbred lines and hybrids compared with KYS standard line.

Maize karyotype variability has been extensively investigated. The identification of maize somatic and pachytene chromosomes has improved with the development of fluorescence in situ hybridization (FISH) using tandemly repeated DNA sequences as probes. We identified the somatic chromosomes of sister inbred lines that were derived from a tropical flint maize population (Jac Duro [JD]), and hybrids between them, using FISH probes for the 180-bp knob repeat, centromeric satellite (CentC), centromeric satellite 4 (Cent4), subtelomeric clone 4-12-1, 5S ribosomal DNA and nucleolus organizing region DNA sequences. The observations were integrated with data based on C-banded mitotic metaphases and conventional analysis of pachytene chromosomes. Heterochromatic knobs visible at pachynema were coincident with C-bands and 180-bp FISH signals on somatic chromosomes, and most of them were large. Variation in the presence of some knobs was observed among lines. Small 180-bp knob signals were invariant on the short arms of chromosomes 1, 6, and 9. The subtelomeric 4-12-1 signal was also invariant and useful for identifying some chromosomes. The centromere location of chromosomes 2 and 4 differed from previous reports on standard maize lines. Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines. The pairing behavior of chromosomes 2 and 4 at pachytene stage in this hybrid was investigated using FISH with chromosome-specific probes. The homologues were fully synapsed, including the 5S rDNA and CentC sites on chromosome 2, and Cent4 and subtelomeric 4-12-1 sites on chromosome 4. This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size. The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

Genome size evolution in Sapindaceae at subfamily level: a case study of independence in relation to karyological and palynological traits

Sapindaceae s.l. is a moderately large family of trees, shrubs and lianas. Current knowledge on genome size and how it varies in this family is scarce. This research aims to characterize the DNA content in 39 species of Sapindaceae, mainly in tribe Paullinieae s.s., by the analysis of the variation in genome size relative to karyotypic and palynological features. Nuclear DNA amount was measured by flow cytometry, and linear regression analyses were conducted to analyse the relationship between genome size variation and various karyotypic and palynological features. Genome size varied nine-fold among species, ranging from 1C = 0.305 pg (Lophostigma plumosum) to 2.710 pg (Cardiospermum heringeri). The low regression coefficients obtained suggest that genome size mainly varies independently of karyotypic and palynological features. With regard to karyotype evolution, the constant chromosome number but variable genome size in Houssayanthus, Paullinia and Serjania suggest that structural changes mainly caused by changes in the amounts of repetitive DNA are more important than numerical change. In contrast, in Cardiospermum and Urvillea, variation in chromosome number and genome size supports the suggestion that numerical and structural changes are important in the karyotype evolution of these genera. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 589–600.

Analysis of repetitive DNA in chromosomes by flow cytometry

We developed a flow cytometry method, chromosome flow fluorescence in situ hybridization (FISH), called CFF, to analyze repetitive DNA in chromosomes using FISH with directly labeled peptide nucleic acid (PNA) probes. We used CFF to measure the abundance of interstitial telomeric sequences in Chinese hamster chromosomes and major satellite sequences in mouse chromosomes. Using CFF we also identified parental homologs of human chromosome 18 with different amounts of repetitive DNA.

Targeted isolation, sequence assembly and characterization of two white spruce (Picea glauca) BAC clones for terpenoid synthase and cytochrome P450 genes involved in conifer defence reveal insights into a conifer genome

BackgroundConifers are a large group of gymnosperm trees which are separated from the angiosperms by more than 300 million years of independent evolution. Conifer genomes are extremely large and contain considerable amounts of repetitive DNA. Currently, conifer sequence resources exist predominantly as expressed sequence tags (ESTs) and full-length (FL)cDNAs. There is no genome sequence available for a conifer or any other gymnosperm. Conifer defence-related genes often group into large families with closely related members. The goals of this study are to assess the feasibility of targeted isolation and sequence assembly of conifer BAC clones containing specific genes from two large gene families, and to characterize large segments of genomic DNA sequence for the first time from a conifer.ResultsWe used a PCR-based approach to identify BAC clones for two target genes, a terpene synthase (3-carene synthase; 3CAR) and a cytochrome P450 (CYP720B4) from a non-arrayed genomic BAC library of white spruce (Picea glauca). Shotgun genomic fragments isolated from the BAC clones were sequenced to a depth of 15.6- and 16.0-fold coverage, respectively. Assembly and manual curation yielded sequence scaffolds of 172 kbp (3CAR) and 94 kbp (CYP720B4) long. Inspection of the genomic sequences revealed the intron-exon structures, the putative promoter regions and putative cis-regulatory elements of these genes. Sequences related to transposable elements (TEs), high complexity repeats and simple repeats were prevalent and comprised approximately 40% of the sequenced genomic DNA. An in silico simulation of the effect of sequencing depth on the quality of the sequence assembly provides direction for future efforts of conifer genome sequencing.ConclusionWe report the first targeted cloning, sequencing, assembly, and annotation of large segments of genomic DNA from a conifer. We demonstrate that genomic BAC clones for individual members of multi-member gene families can be isolated in a gene-specific fashion. The results of the present work provide important new information about the structure and content of conifer genomic DNA that will guide future efforts to sequence and assemble conifer genomes.

Autosomal mutations affecting Y chromosome loops in Drosophila melanogaster

BackgroundThe Y chromosome of Drosophila melanogaster harbors several genes required for male fertility. The genes for these fertility factors are very large in size and contain conspicuous amounts of repetitive DNA and transposons. Three of these loci (ks-1, kl-3 and kl-5) have the ability to develop giant lampbrush-like loops in primary spermatocytes, a cytological manifestation of their active state in these cells. Y-loops bind a number of non-Y encoded proteins, but the mechanisms regulating their development and their specific functions are still to be elucidated.ResultsHere we report the results of a screen of 726 male sterile lines to identify novel autosomal genes controlling Y-loop function. We analyzed mutant testis preparations both in vivo and by immunofluorescence using antibodies directed against Y-loop-associated proteins. This screen enabled us to isolate 17 mutations at 15 loci whose wild-type function is required for proper Y-loop morphogenesis. Six of these loci are likely to specifically control loop development, while the others display pleiotropic effects on both loops and meiotic processes such as spermiogenesis, sperm development and maturation. We also determined the map position of the mutations affecting exclusively Y-loop morphology.ConclusionOur cytological screening permitted us to identify novel genetic functions required for male spermatogenesis, some of which show pleiotropic effects. Analysis of these mutations also shows that loop development can be uncoupled from meiosis progression. These data represent a useful framework for the characterization of Y-loop development at a molecular level and for the study of the genetic control of heterochromatin.

The Distribution of Repetitive DNAs Along Chromosomes in Plants Revealed by Self-genomic in situ Hybridization

The distribution of repetitive DNAs along chromosomes is one of the crucial elements for understanding the organization and the evolution of plant genomes. Using a modified genomic in situ hybridization (GISH) procedure, fluorescence in situ hybridization (FISH) with genomic DNA to their own chromosomes (called self-genomic in situ hybridization, self-GISH) was carried out in six selected plant species with different genome size and amount of repetitive DNA. Nonuniform distribution of the fluorescent labeled probe DNA was observed on the chromosomes of all the species that were tested. The signal patterns varied among species and were related to the genome size. The chromosomes of the small Arabidopsis genome were labeled almost only in the pericentromeric regions and the nucleolus organizer regions (NORs). The signals in the relatively small genomes, rice, sorghum, and Brassica oleracea var. capitata L., were dispersed along the chromosome lengths, with a predominant distribution in the pericentromeric or proximal regions and some heterochromatic arms. All chromosomes of the large genomes, maize and barley, were densely labeled with strongly labeled regions and weakly labeled or unlabeled regions being arranged alternatively throughout the lengths. In addition, enhanced signal bands were shown in all pericentromeres and the NORs in B. oleracea var. capitata and in all pericentromeric regions and certain intercalary sites in barley. The enhanced signal band pattern in barley was found consistent with the N-banding pattern of this species. The GISH with self-genomic DNA was compared with FISH with C ot-1 DNA in rice, and their signal patterns are found to be basically consistent. Our results showed that the self-GISH signals actually reflected the hybridization of genomic repetitive DNAs to the chromosomes, thus the self-GISH technique would be useful for revealing the distribution of the regions where repetitive DNAs concentrate along chromosomes and some chromatin differentiation associated with repetitive DNAs in plants.

Genome size and evolutionary diversification in vertebrates

The possibility that the accumulation and amplification of excess non‐coding DNA may adversely affect the ability to evolve (evolvability) has been suggested for various organisms. In particular, an inverse correlation between genome size and number of species, and a direct correlation between genome size and extinction risk, have recently been established in plants, and in plants and vertebrates, respectively. The present study of a broad sample of vertebrates also evidenced an inverse correlation between genome size, percentage of repetitive DNA and number of species in this subphylum. This correlation is significant only at the higher taxonomic levels and exhibits a different trend in groups with DNA content greater than 5 pg/nucleus compared with those exhibiting lower values. Large genomes may influence the evolvability in multiple ways. Indeed, different correlations have been obtained between genome size, amount of repetitive DNA and various morphological and functional cell parameters with different roles in vertebrate evolution subject to different hierarchical levels of selection. The trend of the correlation between genome size and species number observed in the present study is similar to the one between genome size and extinction risk, and suggests that genome size is not the sole factor exerting a constraint on evolvability, but rather that it is one of a number of factors in a complex hierarchical system within which various evolutionary phases would have been influenced by the interaction among various genomic, cellular and organismic factors.

Autosomal control of the Y-chromosome kl-3 loop of Drosophila melanogaster.

The Y chromosome of Drosophila melanogaster carries a limited number of loci necessary for male fertility that possess a series of unconventional features that still hinder a definition of their biological role: they have extremely large sizes; accommodate huge amounts of repetitive DNA; and develop prominent, lampbrush-like loops that bind a number of non-Y-encoded proteins. To obtain insight into the functional role of the loop-forming fertility factors, we characterized four autosomal male-sterile mutations that identify two loci we named loop unfolding protein-1 (lup-1) and loop unfolding protein-2 (lup-2). Biochemical and ultrastructural analysis revealed that neither of them impairs the synthesis of the putative dynein subunit encoded by the ORF localized within the kl-3 fertility factor. However, the stability of four dynein heavy chains is simultaneously affected in each mutant, together with the regular assembly of the axonemal dynein arms that are either absent or strongly reduced. These results indicate that the synthesis of the kl-3-encoded dynein can be uncoupled from the formation of the corresponding loop and suggest that this structure does not simply represent the cytological counterpart of a huge transcription unit, but must be regarded as a complex organelle serving some additional function necessary for male fertility.

Evolutionary dynamics of grass genomes

SummaryThe grass family (Poaceae) has been the subject of intense research over the past decade. Although other angiosperm families contain more species and more genera, the Poaceae exceed all other families in ecological dominance and economic importance. Research has focused on the evolutionary relationships among grasses as well as the structure of grass genomes. Here I examine the evolutionary dynamics of grass genomes in a phylogenetic framework. It is clear that grass genomes are evolutionarily labile for many characteristics, including genome size and chromosome number. Variation in genome size among grasses probably reflects fluctuations in the amount of repetitive DNA per genome, but the history and causes of chromosome number changes remain unclear. Despite substantial variation among genomes, comparative maps suggest that grass genomes retain extensive regions of colinearity. By reanalyzing some comparative map data and also by reviewing comparative sequence data, I argue that the current colinearity paradigm requires reassessment. Contents Summary 15 I. Introduction 16 II. Grass relationships, chromosome numbers and genome size 17 1. Grass relationships 17 2. The timescale of grass evolution 17 3. The evolution of chromosome number 18 4. The evolution of genome size 19 III. Comparative maps and sequencing 21 1. Comparative maps of the grasses 21 2. Limitations of map data for evolutionary analyses 22 3. Synteny among grass genomes: a reanalysis 23 4. Microsynteny: comparative grass sequences 24 IV. Conclusions 25 Acknowledgements 26

Transposable elements and the evolution of genome size in eukaryotes.

It is generally accepted that the wide variation in genome size observed among eukaryotic species is more closely correlated with the amount of repetitive DNA than with the number of coding genes. Major types of repetitive DNA include transposable elements, satellite DNAs, simple sequences and tandem repeats, but reliable estimates of the relative contributions of these various types to total genome size have been hard to obtain. With the advent of genome sequencing, such information is starting to become available, but no firm conclusions can yet be made from the limited data currently available. Here, the ways in which transposable elements contribute both directly and indirectly to genome size variation are explored. Limited evidence is provided to support the existence of an approximately linear relationship between total transposable element DNA and genome size. Copy numbers per family are low and globally constrained in small genomes, but vary widely in large genomes. Thus, the partial release of transposable element copy number constraints appears to be a major characteristic of large genomes.

Association between divergence and interspersed repeats in mammalian noncoding genomic DNA

The amount of noncoding genomic DNA sequence that aligns between human and mouse varies substantially in different regions of their genomes, and the amount of repetitive DNA also varies. In this report, we show that divergence in noncoding nonrepetitive DNA is strongly correlated with the amount of repetitive DNA in a region. We investigated aligned DNA in four large genomic regions with finished human sequence and almost or completely finished mouse sequence. These regions, totaling 5.89 Mb of DNA, are on different chromosomes and vary in their base composition. An analysis based on sliding windows of 10 kb shows that the fraction of aligned noncoding nonrepetitive DNA and the fraction of repetitive DNA are negatively correlated, both at the level of an entire region and locally within it. This conclusion is strongly supported by a randomization study, in which repetitive elements are removed and randomly relocated along the sequences. Thus, regions of noncoding genomic DNA that accumulated fewer point mutations since the primate-rodent divergence also suffered fewer retrotransposition events. These results indicate that some regions of the genome are more "flexible" over the time scale of mammalian evolution, being able to accommodate many point mutations and insertions, whereas other regions are more "rigid" and accumulate fewer changes. Stronger conservation is generally interpreted as indicating more extensive or more important function. The evidence presented here of correlated variation in the rates of different evolutionary processes across noncoding DNA must be considered in assessing such conservation for evidence of selection.

Grasses as a single genetic system: genome composition, collinearity and compatibility

The best-known grasses are the cereals, of which three speciesrice, wheat and maizeaccount for about half of total world food production. These and other domesticated grasses (including barley, millet, oats, rye, sorghum and sugar-cane) are among the 10-11 thousand species that comprise the grass (Gramineae) family of monocotyledonous flowering plantsL Because of their unrivaled economic importance and relative ease of genetic manipulation, the cereals and forage grasses have been major targets for basic and applied plant science. Each grass species has unique agronomic properties, particularly with respect to environmental preferences and tolerances, and this variation has led to an array of independent research programs for the study and improvement of each grass. Although many individual species have been investigated intensively, the information and materials acquired have not often been used in the full range of grass species. Recent results from genome mapping and intergeneric sexual hybridization experiments suggest that we can now overcome the barriers that have traditionally isolated these systems. These studies show that the various grasses can best be viewed as different manifestations of one tractable genome, and that research priorities should be set to reflect this rich biological potential. Phylogenies based on morphology, molecular sequences and fossils argue that there is a relatively close evolutionary relationship among grass species. The first grass fossils appear in paleocene-eocene deposits some 50-60 million years old z, at a time when modem orders of mammals are known to have existed, and crops were domesticated from their wild progenitors only a few thousand years ago. Grasses are morphologically welldifferentiated from other families and have a single (monophyletic) origin3. Given the close relatedness of the grasses, it is not surprising that many cross-species sexual hybrids have been documented. Moreover, the movement of chromosome segments from one grass species to another has been a powerful tool in both basic and applied plant research. Very wide-ranging crosses between grasses have recently been made, producing transient allodiploidy or chromosomal addition line#. These interspecies and intergeneric hybrids can now be used in traditional mendelian analyses of segregants to identify the genes, mechanisms and designs that underlie the morphological and physiological differences that have evolved in the Gramineae5. Until recently the quality of genetic maps for grasses, including the cereal crops, ranged from fair to non-existent. This general deficiency was rapidly overcome with the advent of maps based on DNA markers. Now, maps have been constructed for all the major cereals, with restriction fragment length polymorphisms (RFLP) and/or randomly amplified polymorphic DNA (RAPD) probes providing anywhere from hundreds to thousands of markers. The first extensive use of DNA markers for the grasses was in studies of maize, and these programs generated large libraries of mapped probes 6-8. The fwst detailed genetic map of sorghum was generated using probes from maize9: when maize probes were hybridized to sorghum DNA, single-o,!?y sequences hybridized well (>95°/6 detected similarly low copy number bands in sorghum under standard high-stringency conditions), while most repetitive sequences hybridized poorly, or not at all. This suggests that the discrepancy in size between the maize and sorghum genomes l°.l~ (the maize genome is 3.5 times larger than that of sorghum) is due, not to differences in the number or types of genes, but rather to differences in the amount of repetitive DNA. Most interestingly,

Genome complexity of the maize rust fungus, Puccinia sorghi

The base composition and complexity of genomic DNA from Puccinia sorghi have been estimated by thermal denaturation, analytical ultracentrifugation, and reassociation kinetics. The buoyant density of genomic DNA in CsCl was found to be 1.7021 g/ml, which corresponds to a GC content of 43%. From thermal denaturation curves the GC content was estimated to be 41%. The haploid genome size of P. sorghi was estimated to be 4.7 × 10 7 bp, half of which represented a moderately repetitive fraction. The size of the P. sorghi genome is similar to that of other basidiomycete fungi; however, the amount of repetitive DNA is greater than that reported for most other fungi.

Polymorphic regions in plant genomes detected by an M13 probe

A sequence containing two clusters of 15 base pair repeats from the protein III gene in the bacteriophage M13 has been shown to detect hypervariable minisatellites in many animal species. We have shown that this M13 fragment will detect similar sequences in higher plants including monocots, dicots, and gymnosperms. In addition, polymorphisms were demonstrated in three dicot species. The amount of this sequence has no relationship with the size of the genome, chromosome number, or amount of repetitive DNA in the species tested.Key words: bacteriophage M13, monocot, dicot, gymnosperm, restriction fragment length polymorphism.

Repetitive DNA interspersion patterns in diptera

AbstractA wide spectrum of repetitive DNA amounts and interspersion patterns is seen in mosquitoes and other dipterans. Using a simple and rapid technique, we show that these range from a minimal amount in five species of Anopheles through moderate amounts in Culex quinquefasciatus to large amounts in Aedes aegypti and Stomoxys calcitrans. Although Culex and Aedes are closely related and both have a considerable amount of interspersed repetitive DNA, the repetitive sequences are different between the two genera. These results and previously published information show that the amount of repetitive DNA and sequences involved have changed many times during the evolution of the Diptera.

Heterochromatin in the genus Artemia

A bisexual species of the genus Artemia (Crustacea, Phyllopoda), Artemia franciscana Barigozzi of San Francisco Bay and a parthenogenetic population of Artemia sp. of Tsing-Tao (China), both with 42 chromosomes, were compared with respect to the microscopic structure of the interphase larval nucleus, the microscopical structure of the prophase chromosomes and the DNA structure. — Artemia franciscana exhibits several chromocenters in the resting nucleus, heterochromatic blocks located at the end of the prophase chromosomes, and a large amount of repetitive DNA (Alu I 110-bp fragments). The other Artemia sp. lacks chromocenters, heterochromatic blocks in the chromosomes, and the Alu I DNA. The two populations thus differ by a remarkable amount of repetitive DNA.