Heteromorphic Chromosome Pair Research Articles

Amplification of a long terminal repeat-like element on the Y chromosome of the platyfish, Xiphophorus maculatus.

The platyfish (Xiphophorus maculatus), in which sex chromosomes are evident from stable and predictable inheritance of sex, is one of the best-studied lower vertebrates with respect to sex determination. In order to identify the structural equivalent for this in the karyotype, which does not contain heteromorphic pairs of chromosomes, two sex-linked molecular probes were used for fluorescent in situ hybridization analysis. One probe, derived from the melanoma oncogene locus ONC-Xmrk, stained both the X and the Y chromosome. This cytogenetic analysis mapped the sex-determining locus to the subtelomeric region of a medium-sized telocentric chromosome. Another probe, a repetitive element (XIR), specifically labeled the Y chromosome in metaphase spreads and in interphase nuclei. The sex chromosomes of X. maculatus can be considered to be at an early stage of evolution of gonosomes. Expansion of the XIR repeat is obviously one of the earliest of the molecular events that lead to divergence of the Y chromosome and recombinational isolation of the sex-determining locus.

Sex chromosome differentiation revealed by genomic in-situ hybridization.

In this work, genomic in-situ hybridization (GISH) was used to study the sex chromosome molecular differentiation on chromosomes of male and female individuals of the isopod crustacean Asellus aquaticus. As a composite hybridization probe, we contemporaneously used male and female whole genomic DNA differently labelled in the presence of an excess of unlabelled DNA of the female homogametic sex. The karyotype of A. aquaticius normally displays eight homomorphic chromosome pairs, but a heteromorphic sex chromosome pair is present in about a quarter of the males of a natural population previously identified by us. GISH did not reveal any sex chromosome molecular differentiation on the male and female homomorphic sex chromosome pair, and the karyotypes of these individuals were equally labelled by the male- and female-derived probe, while the heteromorphic Y chromosome showed a differentially labelled region only with the male-derived probe. This region evidently contains male-specific sequences but, because no similar hybridized region is observed on the male homomorphic chromosome pair, they are probably not important for sex determination but represent a molecular differentiation acquired from the Y chromosome.

Microsatellite (GATA)n reveals sex-specific differences in Papaya

Papaya, an economically important fruit plant, is polygamous in nature. The sex of dioecious papaya plants can be deduced only after they attain reproductive maturity (6–8 months). Normally, 50% of the population in a field is composed of unfruitful male plants and almost 45% of these have to be uprooted at the flowering stage. This unnecessary cultivation of unwanted males leads to wastage of resources, which can be avoided if the sex of the plant is determined at juvenile stage. Morphological and cytological studies conducted so far have failed to differentiate between the various sex forms of papaya. Its dioecious nature, occasional sex-reversal of male flowers and the absence of a heteromorphic pair of sex chromosomes make papaya an interesting system to study sex determination at the molecular level. In the present study, highly informative microsatellite and minisatellite probes were employed to identify sex-specific differences in papaya. Among these, only the microsatellite probe (GATA)4 demonstrated sex-specific differences in all the cultivars analysed. The diagnostic potential of this microsatellite marker was exploited to sex papaya plants at the seedling stage. This study also indicates that the genetic material of the X and Y chromosomes of papaya is diverging in a sex-specific manner and hence they are in the process of differentiation.

Two karyotypes and heteromorphic sex chromosomes in Physalaemus petersi (Anura, Leptodactylidae)

Cytogenetic analyses were performed on specimens from two populations of Physalaemus petersi from three locations in Brazilian West Amazon. Chromosomes from the testis and intestinal epithelium were stained conventionally with Giemsa or C-banded. All animals studied showed a full chromosome complement of 2n = 22, but two distinct karyotypes (I and II) were detected among specimens from one of the populations. Karyotype I specimens showed a XX/XY sex chromosome system and C-band polymorphism. Bivalent chromosomes with heterozygous C-banding frequently lacked chiasmata in the region of this heterochromatin during the first meiotic division. The less common karyotype (II) had a heteromorphic pair of chromosomes, but the relationship of this pair to sex determination could not be elucidated because of the absence of female specimens. Karyotype II was observed in males whose call differed from those of other males in the same population, suggesting that a reevaluation of the taxon P. petersi may be necessary. These results suggest that, in these populations, karyological evolution occurs faster than anatomical evolution.

Cytogenetic Characterization of Sea Trout (Salmo trutta) from Poland

Cytogenetic analysis of two local populations of sea trout (Salmo trutta) revealed a diploid chromosome number (2n) of 80 and a diploid chromosome arm number (NF) of 102. Two heteromorphic chromosome pairs were identified, based on Cbanding and DAPIand CMA3-staining: NOR-bearing pair 11 and metacentric pair 6. The study was designed to search for chromosome markers enabling separation of fish from one of the Pomeranian rivers (Slupia River) compared to those from the Vistula River. Frequencies of the heteromorphic chromosome pairs identified genetic differences between the two groups.

Spermatogenesis in Bovicola limbata Gervais, 1844 and B. caprae Gurlt, 1843 (Phthiraptera, Ischnocera).

Summary Adult males of Bovicola limbata and B. caprae were cytogenetically analyzed. Both species have n=7, holokinetic chromosomes, and achiasmatic male meiosis. As in other species of Phthiraptera, spermatogenesis follows a particular course with mitotic divisions after meiosis; consequently, cysts of 64 active spermatozoa and 64 non-functional cells (pycnotic nuclei) are encountered. In B. limbata an heteromorphic chromosome pair was observed. The results are compared with previous reports in Phthiraptera. The achiasmatic male meiosis, together with the particular course of spermatogenesis and the low chromosome numbers markedly constrain genetic variability.

The karyotype of Alouatta fusca clamitans from Rio de Janeiro, Brazil: Evidence for a y-autosome translocation

The chromosome complements of four males of Alouatta fusca clamitans, caught in Rio de Janeiro State, Brazil, were analyzed by G-, C-, and NOR-banding techniques. The diploid number found was 49 in all the specimens. The presence of a heteromorphic pair of submetacentric chromosomes in the analyzed specimens, not present in males and females with 2n = 50 previously reported, and its G-banding pattern, led us to assume that this pair is involved in a Y-autosome translocation. Thus, the sex determination system appears modified to X1X1X2X2 /X1X2Y. Heterochromatic segments were found in the pericentromeric region of all the chromosomes, in the telomeric region of the short arm in pair 2, in the complete length of the short arm of pairs 5 and 6 and in the intercalary region of the long arm in pair 17. The nucleolar organizer regions were situated in the intercalary region of the long arm in two small acrocentric pairs.

Mitotic analysis of the North American white sturgeon, <i>Acipenser</i> <i>transmontanus</i> Richardson (Pisces, Acipenseridae), a fish with a very high chromosome number

The average chromosome number of the North American white sturgeon, Acipenser transmontanus Richardson, was found to be 271 ± 2.5 (ranging from 265 to 276). This number is significantly higher than previous estimates for this species. A representative karyotype was found to consist of 132 meta- and submeta-centric chromosomes, 44 acrocentric chromosomes, and 98 microchromosomes. An improved C-banding technique revealed variation (2-7) between animals in the number of entirely heterochromatic metacentric chromosomes. These heterochromatic chromosomes may represent supernumerary chromosomes. There was no cytogenetic evidence of a heteromorphic sex chromosome pair or any sex-related chromosomal polymorphism in either sex of this species.Key words: C-banding, fish, karyotype, supernumerary chromosomes, white sturgeon.

Longitudinal differentiation of chromosomes of Asellus aquaticus (Crust. Isop.) by in situ nick translation using restriction enzymes and DNase I.

Asellus aquaticus is an isopod crustacean whose chromosomes cannot be differentiated by G- or R-banding techniques. In this work, we have obtained a longitudinal differentiation of these chromosomes by in situ nick translation using restriction enzymes (HaeIII, DraI and BamHI) and DNase I digestions. The four nucleases, with different efficiencies, have produced similar labelling patterns. Staining with DAPI, Giemsa and chromomycin A3 reveals that the DNA of the nick-translated regions is generally more resistant to extraction from the chromosome. The results obtained on the heteromorphic sex chromosome pair observed in about a quarter of the males of a natural population allow several hypotheses to be advanced on the nature and origin of chromosome dimorphism.

Karyotype Analysis in Three New Species of Echeand (Liliaceae) and Cytotypes of E. reflexa.

Karyotypic analysis of Echeandia hintonii, E. montealbanensis, E. pubescens and three populations of E. reflexa, showed that all of them were diploid with 2n = 16, n = 8 and X = 8. Each species had a distinctive karyotype. Also, each one of the populations of Echeandia reflexa analyzed presented a distinct karyotype. Cytotype variation was observed in heteromorphic chromosome pairs. Meiotic analysis showed heteromorphic exchanges. Analysis ofMI showed heteromorphic IIs, while AI analysis showed U-type chromatid exchanges and subchromatid aberrations. Lagging chromosomes were recorded in AI of E. pubescens and in cytotypes of E. reflexa. Those cytotypes with a larger proportion of chromosomal aberrations, were also those with greater proportion of unviable pollen and a larger value of TCL (genome size). Based on these results and on previous reports, we can suggest that translocations and chromatid exchange, follow a behavior pattern common to species and cytotypes of Echeandia, and that these chromosome aberations have played a major role in the evolution of the genus, providing with a larger potential for colonization and distribution in new habitats.

Chromosomes of four Indian marine catfishes (Bagridae, Ariidae: Siluriformes) with a heteromorphic pair in maleMystus gulio

SUMMARYSomatic chromosomes of four Indian marine catfishes, Mystus gulio, M. vittatus of Bagridae and Arius nenga, A. serratus of Ariidae, were obtained from the gill epithelial cells and their morphometric analyses were done. M. gulio showed 2n = 58, FN = 108 with the chromosome formula 2n = 12m + 34sm + 4st + 8t in female and 2n = 13m + 33sm + 4st + 8t in male, thus showing the heteromorphic pair of sex chromosomes in male which is rare in fishes and has not been reported earlier on this species. In M. vittatus the 2n = 58, FN =110 with the chromosome formula 2n = 10m + 30sm + 12st + 6t were obtained. These data were compared with the available information on these two species and the possible cause of karyotypic variation among them was discussed. The chromosomes of A. nenga and A. serratus were reported for the first time. 2n = 54, FN =108 with 16m + 36sm + 2st for the former and 2n = 56, FN = 112 with 8 m + 24sm + 24st for the latter were determined. A complete revision of the chromosomal studies on ...

Morphological differentiation of a sex chromosome and ribosomal genes in Asellus aquaticus (Crust. Isop.)

The karyotype of the isopod crustacean Asellus aquaticus does not normally display any heteromorphic sex chromosome pair. Some of the males in a wild population of A. aquaticus collected in the Sarno river near Naples do display a heteromorphic chromosome pair. The hetero-morphism is due to the presence of two intercalary heterochromatic areas on one chromosome. This chromosome is inherited through the male line as a normal Y chromosome. The heteromorphic pair has retained the capacity to recombine during meiosis. In-situ hybridization of ribosomal probes, labelled with digoxigenin-dUTP, reveals that ribosomal sequences are associated with both intercalary heterochromatic areas of the heterochromosome. The ribosomal genes are normally telomeric and associated with heterochromatin. After digestion of genomic DNA with BamHI EcoRI and HindIII restriction endonucleases and hybridization with ribosomal probes, the hybridization patterns of the males with the heterochromosome differ from those of the males without the heterochromosome, as well as from those of the females, which are identical. The possible origin of the morphological differentiation of the heterochromosome, and the causes of the differences in the ribosomal DNA restriction patterns linked to the presence of this chromosome, are discussed.

Cis-acting regulation of NOR cistrons in Eleutherine bulbosa (Iridaceae)

In Eleutherine bulbosa the nucleolus organizer region (NOR) is found on the heteromorphic chromosome pair I. This shows a pericentric inversion that accounts for the presence of a metacentric and an acrocentric chromosome, and a tandem NOR duplication in the metacentric homologue. The rRNA genes are located in the secondary constriction and in the nucleolar heterochromatin, as suggested by the silver staining. The nucleolar heterochromatin appears to be slightly undercondensed in order to allow its transcription. The transcriptional activity of each NOR was evaluated by the nucleolar volume or by the secondary constriction extension. This activity was observed in tapetum cells as well as in root tip cells and microsporocytes. In the latter two cell types each homologue produced a similar sized nucleolus, whereas in tapetum cells the NOR of the metacentric chromosome was always hyperactivated whilst that of the acrocentric was underactivated. The hyperactivation was more pronounced in prophase than in interphase but was constant in diploid and tetraploid nuclei as well as in mono-and binucleate cells. This consistent change in the activity level of each homologous NOR was interpreted as being due to cis-acting transcriptional regulation. The possible mechanism of cis regulation is discussed. Cis-acting regulation of NOR cistrons in Eleutherine bulbosa (Iridaceae).

GATA repeats in the genome of Asellus aquaticus (Crustacea, Isopoda)

A 500 bp fragment of Drosophila genomic DNA containing 37 copies of the tetranucleotide GATA was used to probe, by Southern DNA blotting and in situ hybridization, two natural populations of the isopod crustacean Asellus aquaticus collected from the Sarno and Tiber rivers. This species does not have a recognizable sex chromosome pair. In a number of males from the Sarno population chromomycin A3 staining reveals a heteromorphic chromosome pair. The heterochromosome has two blocks of heterochromatin. After digestion of genomic DNA with six restriction endonucleases and hybridization with the GATA probe, the two populations exhibit different fragment length patterns. No sex-linked pattern was observed in either population. In situ hybridization to chromosomes of males and females from the Sarno population does not reveal any sex-specific pattern of labelling and indicates a scattered distribution of GATA sequences on most chromosomes with some areas of preferential concentration. The heterochromatic areas of the male heterochromosome are not labelled.

Cytogenet Genome Res of bisexual/unisexual species of <i>Poecilia</i>

Three populations of the North American cyprinodont fish Poecilia latipinna, considered to be one of the progenitor species of the gynogenetic unisexual P. formosa, were analyzed by C-banding and Ag-staining. C-bands were found to be polymorphic, and Ag-staining showed a high degree of variability in both the number and location of nucleolus organizer regions. The C-banding and Ag-staining patterns allow, to a certain extent, to distinguish individual specimens from each of these populations. Females of the three populations were found to have a heteromorphic chromosome pair, which was frequently identifiable with Giemsa staining and always after C-banding. This pair could be interpreted as sex chromosomes of the ZW/ZZ type.

Cytological studies of Solanum jasminoidesPaxt. var. grandiflorum Hort.

The cytology of Solanum jasminoides var. grandiforum has been investigated. The root tip cells showed 10 homologous pairs and two heteromorphic pairs of chromosomes. The pollen mother cells showed one or two rings or chains of four chromosomes, indicating segmental interchanges in the taxon. The heteromorphism in two pairs of chromosomes is shown to be the result of one of the two interchanges. Various abnormalities such as chromosome lesions, asynapsis, chromosome breakages in prophase and chromatin bridges at anaphase stages were also observed in the PMCs. Only about 20% of the pollen grains were stainable. The plant was completely sterile without fruit set.The cause of abnormalities in chromosome behaviour in S. jasminoides is not clearly known. The irregularities in meiosis found in the taxon are attributed to the two interchanges and consequent changes in the location of controlling sequence which effects related genes controlling meiotic events in a co-ordinate fashion.

Karyological Analysis of Cultured Cells and Regenerated Plants of Cipura paludosa Aubl. (Iridaceae)-A Structural Hybrid

India). Karyological analysis of cultured cells and regenerated plants of Cipura paludosa Aubl. (Iridaceae)-A structural hybrid. Bull. Torrey Bot. Club I 1 5: 280-289. 1988.-Cipurapaludosa, a structural hybrid of the Iridaceae with a heteromorphic pair of long chromosomes, has been investigated in vitro. Propagation as well as regeneration of plantlets from callus culture of quartered bulb scale explants has been achieved successfully on MS medium supplemented with specific growth substances. Calluses revealed a high frequency of diploid mitoses from initiation to 40-week-old cultures, though hyperdiploid and hypertetraploid cells were noted as well. Small chromosomes were more susceptible to numerical alteration, while the long heteromorphic pair of chromosomes was stable. Regenerated plants revealed a relative karyotypic stability. Almost 80% of the plants were diploid with a parental (2Asm-st + 2Bm + 8Cmnm) karyotype. The remaining 20% of the plants were mosaics, with a diploid mode number. Structural alteration of chromosomes was very rare in regenerants but confined to the long chromosomes only. The expected cytological behavior of a structural hybrid in vitro is discussed.

Meiotic behavior in progeny of tissue culture regenerated oat plants (Avena sativa L.) carrying near-telocentric chromosomes

Meiotic behavior was analyzed in 69 progeny of two regenerated oat plants (Avena sativa L.) containing different heteromorphic pairs of chromosomes to evaluate the behavior of the altered chromosomes in succeeding generations after regeneration from tissue culture. Heteromorphic bivalents separated prematurely and lagged during anaphase I in about 9% of the cells. Univalents often divided equationally during the first division, were usually not included in the telophase nuclei during the second meiotic division, and ultimately resulted in micronuclei at the quartet stage. Heteromorphic pairs were found in some progeny plants that behaved either more stably or less stably than the progenitor heteromorphic pairs. These variants may have been due to changes in the deficient chromosomes, which possibly arose from bridges during the previous meiosis. Higher than normal frequencies of bridges were seen at anaphase I in microsporocytes of plants containing heteromorphic pairs. Meiotic behavior of heteromorphic pairs involving a SAT chromosome was compared with that of the respective monosome that had been recovered in progeny of a plant carrying the heteromorphic pair. Quartet micronuclei frequencies indicated that chromosomes from the heteromorphic bivalent were included in microspores at a much higher rate than was the respective monosome. Key words: meiotic behavior, heteromorphic chromosome pair, oats, tissue culture, telocentric chromosomes, variation.

Possible role of heterochromatin in chromosome breakage induced by tissue culture in oats (Avena sativa L.)

Perturbations in the replication of heterochromatic regions during tissue culture may be the cause of chromosome alterations observed in regenerated hexaploid oat plants (Avena sativa L.). An idiogram based on pachytene chromosome analysis was developed depicting the heterochromatin distribution on 17 of the 21 chromosomes. Heterochromatic regions were present pericentromerically on each chromosome, at telomeres in five of the chromosomes, and in the NORs of the three satellited chromosomes. Centromeric heterochromatin covered most of the short arm in several chromosomes. Tritiated-thymidine autoradiography was used to determine the nuclear cycle duration (G1 + S + G2 + mitosis = 0.8 + 5.2 + 0.3 + 3.8h = 10.1 h) in root-tip cells and revealed regions of late replication around the primary and secondary constrictions and at chromosome ends. Replication of heterochromatic regions late in the DNA synthetic period makes it plausible that these regions are more sensitive to nuclear cycle alterations caused by the culture process. Pachytene analysis of a heteromorphic chromosome pair that originated during culture showed the break in the deficient chromosome to be in centromeric heterochromatin. The presence of proximal and telomeric heterochromatin means that bridges resulting from replication problems in these regions could result in various alterations including deficiencies, duplications, and translocations and can account for heterochromatin amplification, all of which have been observed in plants that have been regenerated from tissue culture. Key words: heterochromatin, meiosis, telocentric chromosomes, oats, tissue culture, variation.

Chromosomes of Heterobilharzia americana (Digenea: Schistosomatidae) from Texas

Heterobilharzia americana is 1 of 2 known species of mammalian schistosomes indigenous to North America and is the only species in its genus. Reported vertebrate hosts include dogs, raccoons, nutria, and other wild animals (Goff and Ronald, 1981, American Journal of Veterinary Research 42: 1775-1777). Snail hosts are Fossaria cubensis and Pseudosuccinea columella (Malek, 1967, Journal of Parasitology 53: 700702). Various biological studies have been reported by Malek et al. (1961, Journal of Parasitology 47: 619-623), Lee (1962, Journal of Parasitology 48: 728-739), and others. Grossman et al. (1981, Chromosoma 84: 413-430) briefly described chromosomes of H. americana. They reported a diploid number of 20, with a heteromorphic pair of sex chromosomes in the female (ZW) and a homomorphic pair in the male (ZZ). The present paper contains a more detailed description of the chromosomes of the same strain of Heterobilharzia americana from Texas. The stock of Heterobilharzia was supplied by Dr. Norman C. Ronald, who sent snails (Fossaria cubensis) that had been exposed in his laboratory to multiple miracidia. The miracidia originated from eggs in feces of a naturally infected raccoon that had been collected near College Station, Texas. The snails had been collected from the same area before exposure in the laboratory. Chromosomes studied were from material in sporocysts from 8 snails. The sex of schistosome infection in 5 snails was verified by infection of mice with cercariae and recovery of adult worms. Chromosome preparations were made by airdried methods published earlier (Short and Grossman, 1981, Journal of Parasitology 67:661671). Results are based on observations on over 200 metaphase and prometaphase plates. Measurements (Table I) were made on photographs by means of dividers from 10 male and 10 female plates. The relative length of a chromosome is the quotient of its individual length divided by the length of the haploid complement (which was calculated thus: (2A + 2Z)/2). Each centromeric index was calculated by division of 100 x the length of the short arm by the total individual chromosome length. Table I presents information on relative chromosome lengths, centromeric indexes, and classification following the terminology of Levan et al. (1964, Hereditas 52: 201-220). In favorable preparations, all chromosomes could be identified (Fig. 1). The distal end of the short arm of chromosome 5 is characteristically attenuated, producing a lightly stained area where the nucleolar organizer region appears to be. Occasionally what appears to be a small satellite was seen distal to the lighter area on 5 (Fig. 1 D). On the plates measured (Table I), the centromeric position sometimes was not clear on chromo-