Hypoxylon rubiginosum: Cytology of the ascus and surface morphology of the ascospore

Summary The haploid chromosome number ofHypoxylon rubiginosum is 5. The ascospore is uninucleate when formed, becoming binucleate following a mitosis. One of the nuclei subsequently disintegrates. Maturing ascospores are uninucleate.The morphology of the ascospore, as revealed by the scanning electron microscope, is described. The outer wall layer — the perisporium — shows heretofore undescribed surface fibrils. The possible significance of the fibrils is discussed.Paper No. 3205. Washington State University College of Agriculture Project 1767. This study was supported in part by National Science Foundation Grants GB-5219 and GB-8004.     

An inducible change in state on the chromosomes of Sciara: Its effects on the genetic components of the X

Normally in Sciara males the sex chromosome constitution of the soma (X ^m O) differs from that of the germ line (X ^m X ^p ), the single X being of maternal origin. Males which are patroclinous for their sex-linked genes (X ^p O) are found regularly among the progeny of females heterozygous for any one of a number of X-translocations (X X ^t ). The patroclinous males are almost invariably completely sterile. In the present study a comparison is made of the patroclinous males derived from 5 different X-translocations in S. coprophila. The study includes data on the morphology and sexual behavior of the males as well as the cytology of the testis from late 4th instar through pupal life. The study is oriented towards the basic question of whether the paternally-derived X — normally destined to be eliminated — can function properly when it is retained. The comparative study supports our original suggestion that the patroclinous males arise from no-X eggs following 31 disjunction during oogenesis.Dedicated to Professor J. Seiler on the occasion of his 80th birthday.The studies reported here were supported by the National Science Foundation, grants GB-42 and GB 2857, and in part by Contract No. AT-(40-1)-2690 under the Division of Biology and Medicine, U. S. Atomic Energy Commission.     

Microchromosomes of the Ontario Red Fox (Vulpes vulpes): Distribution of chromosome numbers and relationship with physical characteristics

Studies on the distribution of the microchromosomes of the Ontario red fox (Vulpes vulpes Linn.) were carried out on nine foxes trapped in the wild and 38 foxes maintained in captivity. The microchromosomes varied in number from zero to six resulting in variation in diploid number from 34 to 40. The most common numbers detected were 36 and 37 followed by 38, 35, 39, 40 and 34 in decreasing order of occurence. Both inter-and intra-individual variations in chromosome numbers were found.Elevated microchromosome count was noted to have a positive correlation with the body weight of captive male foxes, however no relationship was found between microchromosome number and body length of male foxes or with the weight or length of female foxes.     

Karyological studies on fifteen forms of amphisbaenians (Amphisbaenia-Reptilia)

The chromosome constitutions of 15 forms (2 acrodonts and 13 pleurodonts) of amphisbaenians belonging to two families and eight genera were studied. The diploid chromosome numbers varied from 30 to 44 with the number of chromosome arms (FN) ranging from 42 to 60. The karyotypes of 12 forms all contained 6 pairs of macrochromosomes with similar morphology and 9 to 12 pairs of microchromosomes. The remaining three species had a higher diploid number (40–44) and a wide variation in chromosome morphology. Karyotype variations were found in the same family, even in the same genus. The lengths of the 6 pairs of macrochromosomes in 5 of the 12 forms were measured and compared. This disclosed similarities in the mean lengths, relative lengths, and arm ratios of those forms. — Chromosome patterns found in the present study support, in general, the classification of amphisbaenians derived from analysis of morphological characters.Supported in part by United Health Foundation of Western N. Y. Research Grant G-66-RP-9, National Cancer Institute, CA-08737 and NSF GB 2460.     

Number and pattern of association of chromonemata in the chromosomes of Tradescantia

Summary Analysis of reconstructions, prepared from electron micrographs of successive longitudinal serial sections, has led to the conclusion that the somatic telophase chromosome of Tradescantia paludosa contains four cytologically separable chromonemata. The four represent a pair of pairs, that is, two diplospiremes — one with its two chromonemata arranged helically in dextrorse relationship, and the other with its two in sinistrorse relationship — which are associated to form a tetraspireme. During anaphase and telophase the tetraspireme constitutes the chromosome; during prophase and metaphase the tetraspireme represents one of the two chromatids of the chromosome, which is accordingly an octospireme in terms of the number of cytologically identifiable chromonemata. Loose intertwining of the two tetraspiremes during late prophase accounts for the so-called relational coiling.This paper is dedicated to Professor Hans Bauer on his sixtieth birthday anniversary in appreciation of his contributions to the development of modern cytology.The work reported here was supported in part by Research Grants GM-10499 from the National Institutes of Health, U.S. Public Health Service, and GB-290 from the National Science Foundation, and in part by a NATO fellowship awarded to E. Sparvoli by the Italian National Council of Research.     

Cytomixis in Lolium perenne

Cytomixis is a spontaneous process occurring through the formation of cytoplasmic bridges between adjacent pollen mother cells. This phenomenon was observed in the pollen mother cells of 3 genotypes of Lolium perenne which had been subjected to directional selection for productivity of green material. — The process has led to the formation of up to 34.8% of PMCs with chromosome numbers deviating from the normal diploid number 2n=14. The abnormal PMCs contained chromosome numbers ranging from 2–56 as observed at first metaphase. — Abnormal PMCs were also observed with approximately the same frequency in Meiosis II. This phenomenon is under genetic control. The evolutionary significance of cytomixis and the cytological consequences are discussed.     

Idiogram and trisomy of the water vole (Arvicola terrestris L.), a favourable animal for cytogenetic research

The chromosomes of the water vole (Arvicola terrestris L.) were investigated in 2 female and 5 male animals from three different parts of Sweden. The somatic chromosomes were studied in direct preparations of cornea and bone marrow and in tissue cultures of testis, lung and heart. Meiosis was studied in one male. The chromosome number was 2n=36. No differences in regard to chromosome number and morphology were found among the seven control animals studied. Different chromosome types are represented and the karyotype of the species is favourable for chromosome studies. — An idiogram of the water vole was constructed from measurements of complete chromosome sets from ten heart cells. — In addition to the above normal material one young water vole, trapped in nature, was found to have 37 chromosomes and was trisomic for the smallest autosome. This autosome had a secondary constriction and took part in satellite associations. The cytologic similarities to Down's syndrome in man are striking and it is hoped that the water vole will become a valuable laboratory mammal, especially for elucidation of the chromosomal mechanisms of non-disjunction. The trisomic water vole had no obvious phenotypic abnormalities, but at least one feature was not within normal limits — its tail was unusually short. Also, the development of certain teeth was somewhat aberrant. Whether short tail and dental deformities are symptoms correlated with trisomy for the smallest autosome in the water vole is an open question so far.     

Cytological analysis of constitutive heterochromatin in two species of birds

Two species of birds, the myna (Acridotheres tristis L.) and the jungle babbler (Turdoides malcolmi Sykes), have been studied cytologically. Their modal diploid numbers are 78±2 and 68±2 respectively. In T. malcolmi the heterochromatin is located on the centromeres of all the macros and most of the microchromosomes, heterochromatin comprises predominantly GC-sequences and at least one pair of microchromosomes is responsible for nucleolus organization. The occasional occurrence of silver deposition on more than one pair of microchromosomes suggests the possibility that more than one pair of micros may be associated with the synthesis of rRNA. The heterochromatin in A. tristis is AT-rich and restricted to the macro-chromosomes, though most of the micros are also C-band positive; no particular chromosome stains with silver nitrate, though when interphase cells are stained with acridine orange the nucleolus is surrounded by brightly fluorescing chromatin. Apparently unlike other species, the microchromosomes in the myna do not harbour NORs.     

A cytological study ofPelargonium sect.Eumorpha (Geraniaceae)

The chromosome numbers of seven species ofPelargonium sect.Eumorpha have been determined from material of known wild origin, and karyotypic comparisons have been made. Within the section there is variation in basic chromosome number (x = 4, 8, 9, 11), variation in chromosome size, and two species have polyploid races. The three species with chromosome numbers based on x = 11 have the smallest chromosomes (1.0–1.5 µm); chromosomes are larger (1.0–3.0 µm) in the other species.P. elongatum has the lowest chromosome number in the genus (2n = 8).P. alchemilloides is exceptional in that it has four cytotypes, 2n = 16, 18, 34 and 36, and the form with 2n = 36 has large chromosomes (2.0–5.0 µm). Evidence from a synthesized hybrid suggests thatP. alchemilloides with 2n = 16 may be of polyploid origin. The three species based on x = 11 appear to be more closely related to species from other sections ofPelargonium that have the same basic chromosome number and small chromosome size, rather than to other species of sect.Eumorpha.     

The somatic chromosome complements of 16 species of falconiformes (Aves) and the karyological relationships of the order

Using short term leucocyte culture techniques, the somatic chromosome complements of 16 species of diurnal birds of prey, belonging to four different families of the order Falconiformes were studied. The karyotypes are described and illustrated, and of some species idiograms are presented. In accordance with the family classification, four karyologically different groups can be distinguished in the Falconiformes: (1) Cathartidae, with karyotypes which show only 7 pairs of biarmed macrochromosomes and a considerable number of small acrocentrics and microchromosomes (the diploid numbers are approximately 80). This is the only group in which really large macrochromosomes are found (over 10% TCL); (2) Falconidae, the karyotypes of which include only a single pair of biarmed macrochromosomes, all other elements being acrocentrics of medium to small size or microchromosomes (diploid numbers of approximately 84 and 52); (3) the secretary bird (Sagittariidae), with 36 biarmed macrochromosomes and 44 small acrocentrics and microchromosomes (2n=80 approximately); (4) Accipitridae, the representatives of which never possess more than about 8 real microchromosomes, while their karyotypes show varying numbers of biarmed and acrocentric macrochromosomes of small to medium size (diploid numbers range from 78 to 60).The possible karyological relationships within each of these groups are briefly discussed, while a more extensive discussion is dedicated to the possible relationships between these groups, and those between them and other avian taxa.The variation in karyotypic structures found in the Falconiformes is much wider than that in other avian groups. However, it remains an unanswered question whether this karyological heterogenelty points to a polyphyletic origin of the diurnal birds of prey. Especially the chromosome complements of the Accipitridae are most uncommon among birds, because of their extremely low numbers of real microchromosomes. However, of all the Falconiformes only the karyotypes of the Cathartidae have clear counterparts outside the order, since nearly identical complements were found in representatives of the Phoenicopteriformes and Gruiformes.The present work was partially carried out at the Institute of Genetics and the Center for Clinical Cytogenetics (both in Utrecht).     

Nonreplication of heterochromatic chromosomes in a mealy bug,Planococcus citri (Coccoidea: Homoptera)

In males of mealy bugs with the lecanoid chromosome system, the paternal set of chromosomes becomes heterochromatic in early embryogeny. In males of the mealy bug, Planococcus citri, the heterochromatic (H) set in testis sheath cells and in most of the oenocytes apparently did not replicate while the euchromatic (E) set was undergoing several cycles of endoreplication. In third instar males, testis sheath cells in endoanaphase and endotelophase exhibited 5H and either 40 or 80E chromosomes. The increase in the number of E chromosomes was attributed to the replication of only the E chromosomes. Oenocytes of third instar males had 0, 5, or 10H chromosomes and from 10 to 240E chromosomes. The oenocytes with 5H chromosomes had a mean of 50.8E chromosomes, and those with 10H chromosomes had a mean of 155.6E chromosomes. Nuclear and cell fusion was considered as a means of producing the various numbers of H and E chromosomes in oenocytes, and it was concluded that although nuclear fusion probably took place, the differences between the number of H and E chromosomes was at least in part due to replication of only the E chromosomes. The size of the H chromosomes was about the same in all the testis sheath cells and the oenocytes irrespective of the level of endopolyploidy for the E set. These H chromosomes apparently did not increase in polyteny, because they were only about half the size of the H chromosomes in prophase I of spermatogenesis. The significance of the nonreplication of the H set and the control of nonreplication are briefly discussed.This study was aided by a grant (GB-1585) from the National Science Foundation, Washington, D.C.     

Reversion of XO to XY sex chromosome mechanism in a phasmid

Summary The sex chromosomes of the male phasmid Isagoras schraderi Rehn comprise an X and a Y, — each with a submedian kinetochore, and one euchromatic and one heterochromatic arm. At meiosis X and Y form an unequal sex bivalent in which the euchromatic arms are terminally associated. Relatively recent reversion from the XO-XX mechanism characteristic of the Phasmidae is indicated by the presence of the euchromatic arm in both X and Y. The diploid number of the male is 34.Unequal autosomal bivalents are found at meiosis in two other species of Isagoras — Isagoras subaquiles Rehn and Isagoras sp. — and in Pseudophasma menius Westwood. The chromosome complements of these species are described.     

Cytogenetics of inherited partial sterility in three generations of the large milkweed bug as related to holokinetic chromosomes

AdultOncopeltus fasciatus males were irradiated with 9000 R of X-rays, and crossed to untreated females. Fertility was reduced to 4.1%. F₁ males and F₂ and F₃ males and females were outcrossed to untreated partners. All F₁ males were partially or totally sterile and a significant number of F₂ and F₃ males and females had reduced fertility. The fertility of each generation was higher than the preceding one, even though the progeny studied in the 3rd generation were selected mostly from low-fertility lines. Cytogenetic studies showed that complex chromosome rearrangements and fragments were transmitted to each generation and were severe enough to account for reduced fertility. — The transmission of complex chromosome rearrangements and fragments for 3 generations of outcrossing correlates with the persistence of sterility in this species possessing holokinetic chromosomes. — Over half the inviable embryos derived from irradiated sperm from P₁ males died in the early stages of development. The inviable embryos produced in later generations died in much later stages of development. — A stable rearrangement of a Y-chromosome fragment translocated to an autosome was isolated from a single F₁ male. This rearrangement was transmitted to all F₂ and F₃ sons. Fertility of the males of this line was reduced to about 75–80%.Supported in part by AEC Contract No. AT(49-7)3028.     

Meiosis in Drosophila melanogaster

Individual bivalents or chromosomes have been identified in Drosophila melanogaster spermatocytes at metaphase I, anaphase I, metaphase II and anaphase II in electron micrographs of serial sections. Identification was based on a combination of chromosome volume analysis, bivalent topology, and kinetochore position. — Kinetochore microtubule numbers have been obtained for the identified chromosomes at all four meiotic stages. Average numbers in D. melanogaster are relatively low compared to reported numbers of other higher eukaryotes. There are no differences in kinetochore microtubule numbers within a stage despite a large (approximately tenfold) difference in chromosome volume between the largest and the smallest chromosome. A comparison between the two meiotic metaphases (metaphase I and metaphase II) reveals that metaphase I kinetochores possess twice as many microtubules as metaphase II kinetochores. — Other microtubules in addition to those that end on or penetrate the kinetochore are found in the vicinity of the kinetochore. These microtubules penetrate the chromosome rather than the kinetochore proper and are more numerous at metaphase I than at the other division stages.     

Mapping of the α4 subunit gene (GABRA4) to human chromosome 4 defines an α2—α4—β1—γ1 gene cluster: further evidence that modern GABAA receptor gene clusters are derived from an ancestral cluster

We demonstrated previously that an α₁—β₂—γ₂ gene cluster of the γ-aminobutyric acid (GABA_A) receptor is located on human chromosome 5q34–q35 and that an ancestral α—β—γ gene cluster probably spawned clusters on chromosomes 4, 5, and 15. Here, we report that the α₄ gene (GABRA4) maps to human chromosome 4p14–q12, defining a cluster comprising the α₂, α₄, β₁, and γ₁ genes. The existence of an α₂—α₄—β₁—γ₁ cluster on chromosome 4 and an α₁—α₆—β₂—γ₂ cluster on chromosome 5 provides further evidence that the number of ancestral GABA_A receptor subunit genes has been expanded by duplication within an ancestral gene cluster. Moreover, if duplication of the α gene occurred before duplication of the ancestral gene cluster, then a heretofore undiscovered subtype of α subunit should be located on human chromosome 15q11–q13 within an α₅—α_x—β₃—γ₃ gene cluster at the locus for Angelman and Prader—Willi syndromes.     

ALTERNATIVE MATING STRATEGIES AND THE EVOLUTION OF SEXUAL SIZE DIMORPHISM IN THE SIDE-BLOTCHED LIZARD, UTA STANSBURIANA: A POPULATION-LEVEL COMPARATIVE ANALYSIS

Population-level comparative analyses can link microevolutionary processes within populations to macroevolutionary patterns of diversification. We used the comparative method to study the evolution of sexual size dimorphism (SSD) among populations of side-blotched lizards ( Uta stansburiana ) . Uta stansburiana is polymorphic for different male mating and female life-history strategies in some populations, but monomorphic in others. We tested whether intrasexual selection among males, fecundity selection on females, and the presence of polymorphic strategies affected levels of SSD. We first resolved a phylogeny for 41 populations across the range of the species and documented a substantial regional structure. Our intraspecific data had significant phylogenetic signal, and correcting for phylogeny using independent contrasts had large effects on our results. Polymorphic populations had male-biased SSD and changes in male body size, levels of tail breaks, and SSD consistent with the intrasexual selection hypothesis. Monomorphic populations had changes in female size, clutch size, and SSD consistent with the fecundity selection hypothesis. Fecundity selection is a likely cause of some monomorphic populations having no SSD or female-biased SSD. Our results suggest that changes in mating strategies are associated with phenotypic diversification and multiple evolutionary forces can shape SSD.     

Tetraploid-octoploid relationships and karyological evolution in the order Acipenseriformes (Pisces) karyotypes,nucleoli, and nucleolus-organizer regions in four acipenserid species

The karyotypes of four Acipenseriformes species, Acipenser gueldenstaedti, 2n=250±8, A. ruthenus, A. stellatus and Huso huso, 2n=118±2, are described. In all four karyotypes the majority of chromosomes are meta- and submetacentric macrochromosomes, and microchromosomes of different morphology make up about one third of the set. In A. ruthenus the NORs are located in the telomeric region of a pair of microchromosomes and at least in one pair of middle-size acrocentrics, and in A. stellatus and Huso huso also in the telomeric regions of at least one pair of microchromosomes. The modal number of active nucleoli in A. gueldenstaedti nuclei amounts to 6–8 (range 2–12), in A. ruthenus, A. stellatus and H. huso nuclei to 2–3 (range 1–6). The data obtained point to the tetraploid origin of Acipenseriformes species with 120 chromosomes and to the octoploid origin of species with 240–260 chromosomes.     

Further studies on polyploid amphibians (Ceratophrydidae)

Meiosis and sex-ratio of artificial interspecific triploid hybrids (3n=33) produced by mating of Odontophrynus cultripes males (2n=22) with O.americanus females (4n=44) are described. — Metaphases I from the triploids show pairing of homologues in configurations of trivalents, bivalents and univalents. Metaphases II revealed a variation of chromosome numbers in the range of 11 to 22. Buploid gametes with 11, 22 and 33 dyads were also found. The latter (3n) arose by pre-meiotic duplication of the chromosomes and/or by absence of meiotic reduction. — Sex-ratio of 11 males to females in one sample of the triploid interspecific hybrids was obtained.This work was supported by U. S. Public Health Service grant GM-14577-03 from the National Institute of General Medical Sciences, by the Fundo de Pesquisas de Instituto Butantan and by the Conselho Nacional de Pesquisas.     

Freeliving marine nematodes from East African coasts.Bathyepsilonema anulosum sp.n. andLeptepsilonema richardi sp.n.

Two new epsilonematid nematode species from Kenyan intertidal areas are described:Bathyepsilonema anulosum sp.n. — characterized by the large number of body-annules (118–124); small unispiral amphid, straight ambulatory setae and the very small copulatory thorns of the males — andLeptepsilonema richardi sp.n., — characterized by the sexual dimorphism in the amphid, the ornamentation of the body cuticle and the umbrella shaped capitulum in the males.     

Chromosome abnormalities in early chicken (Gallus domesticus) embryos

Chromosome studies were undertaken to determine if early embryonic mortality in chicken (Gallus domesticus) embryos is associated with chromosome aberrations. A rapid cytological technique was developed for screening large numbers of embryos for euploidy and aneuploidy. — Of 115 embryos examined, 6 or 5.2% had aberrant chromosome complements. All of these chromosome aberrations occurred in embryos that were phenotypically abnormal. Of 45 macroscopically abnormal embryos, 13.3 % were chromosomally aberrant. These included two cases of haploidy (A-Z), one case of trisomy-1, a case of trisomy-2 and two cases of triploidy (3A-ZZW and 3A-ZWW). — Possible modes of origin for euploid and aneuploid embryos are discussed and consideration given to the significance of these aberrations in relation to embryo viability, constancy of chromosome numbers and nucleolar organization.