Multiple Sex Chromosome System Research Articles

Cytogenetics of the genus Dundocoris Hoberlandt (Heteroptera, Aradidae, Carventinae) where chromosome fusion played the dominant role in karyotype evolution

Abstract More than 260 individuals belonging to 17 taxa (species and subspecies) of the genus Dundocoris from South Africa were cytogenetically investigated. Of the 17 taxa, six have a chromosome number of 2n(♂) = 28XY, six have 2n(♂) = 26XY and one each has 2n(♂) = 27 X1X2Y, 20XY, 14XY, 9XY1Y2 and 7XY1Y2 respectively. The autosomal karyotypes of all the taxa with 28XY are very similar while the largest autosome of the 26XY taxa varies greatly in size. It is concluded that 2n(♂) = 28XY is the ancestral chromosome number of Dundocoris and that it shares this ancestral number with genera like Miteronotus and Trichocarventus. The other chromosome numbers originated from chromosome fusions and 23 fusions, of which four were between autosomes and sex chromosomes, probably took place in the karyotype evolution of the investigated taxa. These are the first recorded cases in the Heteroptera where autosome-sex chromosome fusions gave rise to multiple sex chromosome systems. In D. flavilineatus ndabeniensis an auto...

Karyotypic studies on two Hoplias malabaricus populations (Characiformes, Erythrinidae) of the 2n=42 group, from the first plateau of the Iguaçu river basin (Paraná State, Brazil)

Abstract Hoplias malabaricus represent a clear example of a species complex, including several karyotypic forms with chromosome numbers ranging from 2n=39/40 to 2n=42, including cases of simple and multiple sex chromosome systems. In this work were cytogenetically analyzed two populations of this “species”. The samples were obtained at the first plateau of the Iguacu river (Paranatate, Brazil). The results show that both populations have the same chromosome number (2n=42) but one of them appears to be characterized by a sex chromosome system with male heterogamety (XX/XY). A such system was also previously described in H. malabaricus from another Brazilian region. Thus, the presence of this differentiated sex chromosome system in this river basin suggests that it was originated before the geographic isolation of the studied populations. The present data represent an additional support for the proposition that Hoplias malabaricus constitutes a species complex.

Cytogenetics of nine species of mediterranean blennies and additional evidence for an unusual multiple sex-chromosome system in Parablennius tentacularis (Perciformes, Blenniidae).

The chromosomal complements of nine species of Blenniidae (Aidablennius sphylnx, Blennius ocellaris, Lypophris adriaticus, L. pavo, L. trigloides, Parcablennius gattorugine, P. ponticus, P. sanguinolentus, P. tentacularis) from the Adriatic Sea were analysed with several banding methods and in-situ hybridization. In all species, the diploid set consists of 48 mostly acrocentric chromosomes and has a similar location (terminal centromeric) of NORs, except for L. pavo (interstitial pericentric) and P. ponticus (terminal on the long arm). There are major differences in karyotype with regard to the amount and distribution of heterochromatin. Parablennius tentacularis shows a distinctive sex-chromosome system involving 2n = 48 males with a large totally heterochromatic Y chromosome, and males with 2n = 47. This difference is likely to be the consequence of a translocation of an autosome on the original Y. This finding constitutes an additional instance of the great variability in origins of multiple sex chromosome systems in vertebrates.

Banding patterns, multiple sex chromosome system and localization of telomeric (TTAGGG)n sequences by FISH on two species of Polychrus (Squamata, Polychrotidae)

Karyotypes of Polychrus acutirostris and P. marmoratus after differentialstaining are reported for the first time. P. acutirostris presents 2n=20 (females) and 2n=19 (males). The differential diplo...

Morphologically differentiated sex chromosomes in neotropical freshwater fish.

A general survey of the occurrence of morphologically differentiated sex chromosomes in the neotropical freshwater fishes is presented. The total number of 32 occurrences involving simple XX-XY and ZZ-ZW, and multiple X1X2Y, XY1Y2 and ZW1W2 sex chromosome systems is described, with comments on the aspects of sex chromosome evolution in this fish fauna. The occurrence of different sex chromosome systems in related species of the same genus, or in different populations of the same nominal species, involving male and sometimes female heterogamety, and differences in the molecular composition of sex-linked heterochromatin, are considered as indicative of the early stage of sex chromosomes evolution in fish.

Differentiation and the polymorphic nature of the Y chromosomes revealed by repetitive sequences in the dioecious plant, Rumex acetosa.

The dioecious plant Rumex acetosa has a multiple sex chromosome system: females are 2n = XX + 12, males are 2n = XY1Y2 + 12, and the two Y chromosomes are heterochromatic. A DNA sequence abounded in the mare genome was isolated and analyzed. The sequence (RAE180) was a 180-bp-long tandemly arranged repetitive sequence, distributed in chromosomes Y1 and Y2, and two pairs of autosomes. Both Y chromosomes contained large amounts of RAE180 and the sequence formed many DAPI bands, while, on the two pairs of autosomes, RAE180 did not form DAPI bands. The internal structure and morphological changes of the Y chromosomes were analyzed by FISH, using RAE180 and the Y-chromosome-specific sequence RAYSI as probes. The pattern of the FISH signals caused by the accumulation of RAE180 and RAYSI suggested the structural change in the Y chromosomes during the process of sex chromosome evolution, and the morphological change in the Y chromosomes was explained by reciprocal translocation and inversion.

Sex chromosome evolution in fish. II. Second occurrence of an X1X2Y sex chromosome system in Gymnotiformes.

A multiple sex chromosome system of the X1X1X2X2:X1X2Y type is reported to occur in the fish species Brachyhypopomus pinnicaudatus (Gymnotiformes, Hypopomidae), being the second occurrence of this sex chromosome system in Gymnotiformes and the fifth among Neotropical freshwater fish. The possible origin of this system was hypothesized to be a centric fusion, which occurred in an ancestral form, of two medium-sized acrocentrics, giving origin to the metacentric neo-Y. Heterochromatic DAPI-positive regions were visualized in the pericentromeric region of all the chromosomes, including the Y-chromosome. In-situ hybridization with (TTAGGG)n (all-human-telomeres probe) did not detect any telomeric interstitial regions (ITS), indicating a possible loss of terminal segments of the chromosomes involved in the neo-Y formation.

Chromosome painting of Y chromosomes and isolation of a Y chromosome-specific repetitive sequence in the dioecious plant Rumex acetosa.

The dioecious plant Rumex acetosa has a multiple sex chromosome system: XX in female and XY(1)Y(2) in male. Both types of Y chromosome were isolated from chromosome spreads of males by manual microdissection, and their chromosomal DNA was amplified using degenerate oligonucleotide primed-polymerase chain reaction (DOP-PCR). When the biotin-labeled DOP-PCR product was hybridized with competitor DNA in situ, the fluorescent signal painted the Y chromosomes. A library of Y chromosome DNA was constructed from the DOP-PCR product and screened for DNA sequences specific to the Y chromosome. One Y chromosome-specific DNA sequence was identified and designated RAYSI (R. acetosa Y chromosome-specific sequence I). RAYSI is a tandemly arranged repetitive DNA sequence that maps to the 4',6-diamidino-2-phenylindole bands of both Y chromosomes.

Comparative cytogenetics in Apareiodon affinis (Pisces, Characiformes) and considerations regarding diversification of the group

Comparative cytogenetic studies in Apareiodon affinis (Pisces, Characiformes) from two hydrographic Brazilian basins showed significant divergences related to the general karyotype structure, C‐banding and nucleolar organizer region (NOR) bearing chromosomes. In the upper Parana basin population, distinct diploid numbers were observed among sexes, the females showing 2n = 55 and the males 2n = 54 chromosomes, characterizing a multiple sex chromosome system of the ZZ/ZW1W2 type. A diploid number equal to 54 chromosomes was found for the Cuiaba river population, without a sex chromosome heteromorphism. However, the occurrence of acrocentric chromosomes represents an unique character for this population. These karyotypic differences indicate that the analyzed populations must represent distinct Apareiodon species.

Mapping the distribution of the telomeric sequence (T2AG3)n in the Macropodoidea (Marsupialia), by fluorescence in situ hybridization. I. The swamp wallaby, Wallabia bicolor.

Thylogale spp. (pademelons) retain the plesiomorphic (ancestral) 2n = 22 karyotype for the marsupial family Macropodidae (kangaroos and wallabies). The swamp wallaby, Wallabia bicolor, has the most derived macropodid karyotype with the lowest chromosome number (2n = 10 female, 11 male), and a multiple sex chromosome system (XX female, XY1Y2 male). All but one of the W. bicolor chromosomes are fusion chromosomes. Two of these chromosomes, the X chromosome and chromosome 1, are composed of three plesiomorphic Thylogale-like chromosomes. The distribution of the vertebrate telomeric sequence (T2AG3)n was examined by fluorescence in situ hybridization (FISH) in both species and a 'map' of non-telomeric (T2AG3)n sites on W. bicolor chromosomes relative to Thylogale chromosomes was constructed. (T2AG3)n signals were observed at six fusion sites in the four fusions chromosomes examined, indicating that the (T2AG3)n sequence is consistently retained during fusions. The distribution of the interstitial signals on the long arm of chromosome 1 of W. bicolor and the X chromosome suggests how a combination of inversions, fusions and centromeric transpositions have resulted in interstitial telomeric sequence.

The X1X2Y sex chromosome system in the fish Hoplias malabaricus. II. Meiotic analyses.

The neotropical fish Hoplias malabaricus shows diversified cytotypes and may represent a group of distinct species. One of these cytotypes is characterized by 2n = 40 and 2n = 39 chromosomes in females and males, respectively, with a multiple sex chromosome system of the X1X1X2X2/X1X2Y type. The Y, representing a large chromosome in male karyotype, is derived from a translocation event between two biarmed chromosomes: one of them similar to X1 chromosome (no. 6) and another one similar to X2 chromosome (probably no. 20). Meiotic data (standard and synaptonemal complexes analyses) show 18 bivalents and one characteristic trivalent in pachytene and metaphase I spermatocytes, as well as two kinds of metaphase II cells with 19 and 20 chromosomes. The trivalent is formed by the Y, X1 and X2 chromosomes and usually presents a complete pairing in pachytene. However, trivalents with partially or fully asynapsed segments are also observed. These segments are assumed to be non-homologous regions of the X1 and X2 chromosomes without correspondence with the Y chromosome, which can heterosynapse. This behaviour of the sex trivalent leading to a fully paired structure, taken together with the close frequencies of the two spermatocyte types at metaphase II, suggests a normal pattern for male H. malabaricus meiosis, representing a stabilized multiple sex chromosome system in this species.

New chromosomal findings on Tenebrionidae (Coleoptera) from the Western Mediterranean

SUMMARYThe chromosome numbers and meioformulas of ten species and subspecies belonging to Tenebrionidae (Coleoptera) are presented. Nine species have 2n = 20 and 9 + Xyp meioformula. These chromosomal data agree with the modal number for the approximately 200 species of Tenebrionidae currently studied. The case of Blaps bedeli tones-salai Espanol is an outstanding exception since it presents 15 autosomal bivalents and a multiple sex-chromosome system. Such a departure from normality is discussed within a phylogenetic framework.

Chromosomes in two stilt bug speciesMetatropis rufescensHerrich-Schaeffer ssp.linneaeWagner andBerytinus minorHerrich-Schaeffer (Berytidae, Heteroptera)

SUMMARYThe karyotypes of two stilt bug species Metatropis rufescens (Herrich- Schaeffer) ssp. linneae Wagner and Berytinus minor (Herrich-Schaeffer) (Heteroptera, Berytidae) were reinvestigated by an improved method to analyze chromosomes and their meiotic behaviour. The chromosome formula 2n (♂) = 18 + XY for M. rufescens ssp. linneae was confirmed and a novel chromosome formula for B. minor, 2n (♂) = 42 + X1X2X3Y, was given. This is the first finding of multiple sex chromosome system in this family. Male meiosis is chiasmatic for autosomes. Sex chromosomes undergo post-reductional meiosis. C-banding method revealed heterochromatic bands near one of the telomeres in some but not in all chromosomes in M. rufescens ssp. linneae. The present data on chromosomes in the family Berytidae are discussed.

Meiotic behavior of the X1X2Y1Y2 quadrivalent of the primate Alouatta caraya.

A multiple sex chromosome system was found in three unrelated individuals of the primate Alouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (AY and YA), which are the translocation products. In metaphase I of male meiosis, there is a very long chain quadrivalent in which the order of the element is: X-YA-A7-AY. Segregation in the quadrivalent is alternate and gives balanced products. Synaptonemal complex karyotypes at pachytene show the structure of the quadrivalent made by the four axes. There is a slight difference in the relative length of AY and YA and the kinetochore of A7 aligns with that of AY. The synaptic pattern and changes in the quadrivalent during pachytene are described. Thin sections of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other members of the genus Alouatta.

Sex‐determining mechanisms in squamate reptiles

AbstractTwo modes of sex determination occur in squamates: genotypic sex determination (GSD) and temperature‐dependent sex determination (TSD). Within each of these two major modes, there are many different variants, or mechanisms. Male heterogamety, female heterogamety, multiple sex chromosome systems, and homomorphic sex chromosome systems are all types of GSD found in squamates. Two patterns of TSD have been reported.Only three snakes have been investigated for their sex‐determining mechanisms, each having GSD, although incubation temperature does cause differential mortality and affects post‐hatching physiology. Less than 50 lizard species have been investigated, but there is considerable diversity in the sex‐determining mechanisms reported thus far. Apparently, TSD (and/or GSD) has evolved multiple times within a given taxon. Presently, both GSD and TSD are found in the Agamidae, Eublepharidae, and Gekkonidae, and possibly in the Iguanidae, Lacertidae, and Varanidae as well. Only GSD has been reported for the Scincidae and Teiidae.Correlations within the Eublepharidae suggest an adaptive explanation for the evolution of sexdetermining mechanisms; a shift from male‐larger dimorphism to female‐larger (or no sexual size dimorphism) is accompanied by a shift in sex‐determining mode. These shifts are in agreement with similar correlations observed in turtles. © 1994 Wiley‐Liss, Inc.

Cytogenetic and molecular analysis of the multiple sex chromosome system of Rumex acetosa

A repeated sequence of 180 bp in tandem array has been isolated from the dioecious plant species Rumex acetosa which has a multiple sex chromosome system, XX♀/XY1Y2♂. There are two or three thin C-bands on the X while the Ys are almost entirely heteropycnotic and DAPI-positive but contain no C-band material. The Ys thus represent massive blocks of facultative heterochromatin. The 180 bp sequence has been localized to the X and both Y chromosomes by in situ hybridization. The molecular data support an origin of the sex-multiple from a homomorphic chromosome pair rather than from a sex chromosome/autosome translocation.

Cytotaxonomy of antarctic teleosts of the Pagothenia/Trematomus complex (Nototheniidae, Perciformes)

The interspecific relationships and taxonomy of 12 antarctic coastal Nototheniids (the Pagothenia/ Trematomus complex) are still under discussion. Here we present karyological data on eight species in hope that further cytogenetic data can help to clarify phylogenetic problems. Pagothenia bernacchii (2n = 48) has a generalized karyotype which has not developed heterochromosomes. P. hansoni, P. borchgrevinki and Trematomus newnesi share very similar karyotypes with 2n = 46 for females and 2n = 45 for males. The difference between sexes is probably due to the development of a multiple sex-chromosome system with a neo-Y, typical of males, which originated from a centric fusion of an autosome (now X2) with an undifferentiated Y. The chromosome morphology of the three species seems to be related to that of P. bernacchii. T. nicolai (2n = 58, 57) has a karyotype numerically and morphologically divergent from that of the above species; T. nicolai males may have developed a neo-Y through a tandem translocation. T. pennellii (2n = 32), T. loennbergii (2n = 28; 2n = 30 in a single female) and T. eulepidotus (2n = 24) show karyotypes with progressively fewer chromosomes but with an increasing number of large, bi-armed chromosomes. Such a “symmetrization” process is generally found in advanced poikilothermic Vertebrates and the three species of Trematomus could therefore be considered as karyologically derived. However, parallelism in the karyotype differentiation producing convergence in the chromosome morphology of distantly related species cannot yet be excluded.

A multiple sex-chromosome system in Antarctic ice-fishes

We have studied the chromosomes of 11 of the 15 known species of the notothenioid family Channichthyidae, the specialized whiteblooded Teleosts endemic to the Southern Ocean (ice-fishes). In the female sex, all studied species have the same diploid number of forty eight mostly acrocentric (uniarmed) chromosomes; however there is an interspecific variability in the chromosome morphology, type and quantity of repetitious DNA (usually seen as heterochromatin) localization of silver-stained nucleolar organizers. At least five of the studied species show a multiple sex-chromosome system possibly originated by the translocation of an autosome on an early Y gonosome morphologically similar to the X: the digametic males (2n = 47) show a X1Y X2 and the homogametic females (2n = 48) a X1X1X2X2 gonosomic constitution. This peculiar sex determining mechanism, otherwise rare in Teleosts, can be considered apomorphic in the same way as other morphofunctional characters usually interpreted as adaptive in these fishes.

Sex chromosome systems of European noterid beetles (Coleoptera, Adephaga: Noteridae)

AbstractThe karyotypes and sex chromosome systems of the four European species of noterid beetles are described. Chromosome preparations were made from the mid-gut and testes of adult beetles by acetic acid spreading. Canthydrus diophthalmus was found to have a chromosome compliment of 2n = 16 + XX/XY. A multiple sex chromosome system was common to the three species of Noterus investigated (2n = 18 + X1X1X2X2/X1X2Y). The behaviour of Noterus sex chromosomes during early meiosis was examined and is discussed, along with the occurrence of multiple sex chromosome systems in other Adephaga.

Dosage sex-chromosome systems in plants

Dosage sex-chromosome systems have been detected in two genera of flowering plants. Rumex and Humulus. In Rumex subgenus Acetosa dioecious species have a multiple sex chromosome system with two X chromosomes in females and an X and two Y chromosomes in males. The Y chromosomes are facultatively heterochromatic appearing as chromocentres in somatic interphase nuclei, but undergo RNA transcription, show DNase-I sensitivity, and are genomically-similar to the rest of the complement. Sex determination is dependent on X/autosome balance, and androecium development is not dependent on the presence of Y chromosomes. Intermediate X/autosome ratios between 0.5 and 1.00 give hermaphrodite individuals. The autosomes also affect sex expression, with some enhancing male and others female development. Disomy for one quarter of an X-chromosome is sufficient for functional female development. Y-chromosomes act sporophytically and are required for meiotic success, although a complete Y-complement is not a haploid requirement for pollen maturation or fertilisation. The American annual species R. hastatulus is polytypic for sex-chromosomes and has features both of X/autosome balance and active-Y systems. Humulus lupulus (hop) is highly polytypic with at least six sex-chromosome types. The dosage system is similar to that of Rumex although Y-chromosomes are required for successful pollen maturation. In Humulus dioecy is less strict than in Rumex and a simple synthetic hormone treatment is able to induce male flowers on a female cultivar.