Haploid Chromosome Complement Research Articles

CYTOTAXONOMY OF THE CHARACEAE: KARYOTYPE ANALYSIS OF NITELLA OPACA AND NITELLA FLEXILIS

The haploid chromosome complement of Nitella flexilis (n = 12) is composed of two quite different basic karyotypes. One of these is symmetrical and appears to be identical to the karyotype of N. opaca (n = 6), and the other is quite asymmetrical and seems to be identical to that of an apparently undescribed dioecious Nitella from Kansas (n = 6). This may indicate that the monoecious N. flexilis has arisen through hybridization between two dioecious species. Although heteromorphic sex chromosomes were not observed in either species, it appears that female and male potentialities are confined to separate basic chromosome complements and mechanisms determining the monoecious and dioecious states are in close relation to ploidy.

A Preliminary Report on a Perfect Family of Exclusively Protosexual Yeasts

SUMMARYThe new family, Chlamydozymaceae, consists of yeasts that possess both the basic haploid complement of chromosomes and twice this number. Changes in ploidy occur abundantly among vegetative cells. The life cycle does not include the formation of fruiting bodies, ascospores, basidiospores, or other sexual spores. These are expressions of a type of sexuality designated as protosexuality. Strong sexual expressions include heterothallism, sexual agglutination, conjugation, interspecific and intergeneric hydribidization, and rapid return from the active bisexual to the unisexual state. The new family evidently also includes slow-growing bisexual dikaryons and fast-growing bisexual diploids. In these yeasts protosexuality is true sexuality; consequently, they should be considered as perfect species. They are placed in the family Chlamydozymaceae, which is designated as perfect, and their nomenclature is treated accordingly.Protosexuality is considered to be the evolutionary state of sexual reproduction that preceded the development of fruiting bodies and sexual spores in the Ascomycetes and Basidiomycetes. The new family is believed to be more primitive than either of these two classes and occupies an intermediate position between the most primitive of their genera. Eventually the Chlamydozymaceae may be found to include most of the nonascosporogenous and nonbasidiosporogenous yeasts. If this proves to be true, probably the family should be included in a protosexual taxon of higher rank. The first genus placed in the new family is Chlamydozyma, the type genus, whose affinities are with the Ascomycetes. The type species of Chlamydozyma hybridizes with the type species of Metschnikowia, which has both protosexual and ascosporic stages. Metschnikowia is the most primitive genus of a line of animal and plant pathogens.

A Cytological Study of the Parthenogenetically Developing Turkey Germ Discs and Embryos

1. Diploidy is the prevailing chromosomal complement in parthenogenetically developing turkey germ discs and embryos.2. The modal chromosomal count in normal turkey embryonic material is 72. On the basis of their size the chromosomes can be classified into macro-chromosomes and micro-chromosomes. The former can be further subdivided into two subgroups: (a) the largest eight are very conspicuous both in shape and size (because of this they have been used as markers in this study for ascertaining ploidy in the parthenogenetic material); (b) about ten middle-sized chromosomes.There are approximately 54 micro-chromosomes, with the number varying among the individual embryonic specimens, and within cells of the same specimen.3. The available parthenogenetic material has demonstrated the presence of two small, V-shaped chromosomes in the metaphase nuclear plates. These chromosomes were classed as sex chromosomes because of sex dimorphism in their number. On the basis of this, the genetic sex of the membranous growths and of embryos was determined to be male.4. In addition to normal diploid cells, the parthenogenetic specimens showed numerous polyploid (mostly tetraploid) plates. These were interpreted to be the product of the restitution nuclei fused into one, or of mitotic divisions in the binucleated cells.5. Small nuclear plates, interpreted to possess the haploid chromosomal complement, also occurred frequently in the parthenogenetic material. The occurrence of such plates may be a major factor responsible (either per se or due to recessive lethals) for the abortive nature of most of the instances of parthenogenetic development in turkeys.

The chromosome complement of the rhesus monkey (Macaca mulatta) determined in kidney cells cultivated in vitro.

The chromosome complement of male and female Rhesus monkey has been investigated in kidney cells cultivatedin vitro for 3 to 6 days. The chromosome number is 42. The Y chromosome of the heterogametic male is the smallest element in the complement, and it is acrocentric. The X chromosome ranks eigth in decreasing order of size and typically has an arm ratio of 1.4. The autosomes form a graded size series of metacentric chromosomes, 3–15μ long in early metaphase, and with arm ratios from 1.1 to 3.3. Chromosome IX carries a large secondary constriction near the centromere; it is presumed to be the main nucleolar chromosome. A smaller secondary constriction is found consistently in the long arm of chromosome I. The X chromosome and chromosome XXI appear to be dimorphic in the limited population studied, the alternative forms differing in arm ratios but not in total length. An idiogram of the haploid chromosome complement is presented incorporating measurements of 10 completely analyzed nuclei, five from male monkeys and five from females. On the basis of relative length, arm ratio, and occurrence of secondary constrictions, most chromosomes of the complement can be individually identified.

APOMIXIS IN PASPALUM SECANS

THE OCCURRENCE of apomixis in Paspalum notatum has been demonstrated by Burton (1948) on the basis of breeding tests in which a male-sterile plant was pollinated with pollen from a plant having a dominant marker gene. More recent studies also have established the occurrence of apomictic phenomena in two additional genera of the tribe Paniceae which are rather closely related to Paspalumr. Facultative apomixis, involving somatic apospory, the production of two distinct types of female gametophytes, and pseudogamy, has been reported by Warmke (1954) in Panicum maximum. Closely comparable phenomena have been found in several species of Pennisetum by Narayan (1951), and Snyder et al. (1955). Preliminary studies of microsporogenesis in several strains of Paspalum secans Hitchc. and Chase revealed extensive meiotic irregularity, the most striking features being almost complete asynapsis or desynapsis of the chromosomes and the production of dyads of microspores. The species is represented in the vicinity of the type locality of Mayagiiez, Puerto Rico, by a number of distinguishable morphological types, which exhibit appreciable differences in percentages of pollen stainability and seed set. The progenies of individual plants were found to be very uniform and all plants that were examined had the tetraploid chromosome number 2n 40; although the extent of meiotic irregularity in microsporogenesis would apparently preclude the formation of pollen with normal haploid chromosome complements. This paper presents the results of an investigation of megasporogenesis, megagametogenesis, and the role of pollination in this species. Details of meiotic behavior and microsporogenesis will be presented in a sub. sequent paper. MATERIALS AND METHODS.-Most of the material for the present study was obtained from three plants that had been transplanted into a grass nursery for convenience in handling. Herbarium specimens from these plants have been deposited in the U.S. National Herbarium. Limited material from a number of other plants growing under natural conditions in the vicinity of Mayagiiez also was studied. Material for the study of megasporogenesis and megagametogenesis was killed in formalin-aceticalcohol (70 per cent alcohol) after the florets had been removed from the inflorescences and the distal

CYTOLOGICAL STUDIES OF ASCUS DEVELOPMENT IN COCHLIOBOLUS SATIVUS

Conjugate divisions occurred in the binucleate crozier of Cochliobolus sativus (Ito & Kurib. ex Kurib.) Drechs. ex Dast. Two cross walls were laid down in such a way that the penultimate cell was binucleate. A lateral bulge developed in this cell and it quickly assumed the clavate shape of the young ascus. The two nuclei in the clavate ascus fused and this was accompanied by a fusion of their nucleoli. In meiosis two divisions occurred with pairing between highly contracted chromosomes early in the first division. A third division (mitotic) followed and resulted in the formation of eight haploid nuclei. Ascospore delimitation began at this stage and each spore was initially uninucleate. Evidence of structural hybridity was seen in all divisions in the ascus. The haploid chromosome complement, as determined from pachytene and metaphase stages, consisted of seven or eight chromosomes.

A CYTOLOGICAL STUDY OF ASCUS DEVELOPMENT IN PYRONEMA CONFLUENS TUL.

A cytological study of Pyronema confluens has revealed that only one meiosis occurs in the ascus, and that the haploid chromosome complement is probably 12. Differences in size and staining properties were noted between nuclei of the ascogenous hyphae and paraphyses. Diplotene chromosomes are linearly differentiated into heterochromatic knobs and achromatic intercalary segments that could not be differentiated from the cytoplasm with either basic fuchsin or propiono-carmine.

Karyotype Analysis in Gymnospermae, I

The karyotype analysis of Ginkgo biloba L. has been studied in the mitotic cells of young leaf meristems. The basic number (b) is twelve. A haploid chromosome complement in both sexes contains two submedian and ten subterminal chromosomes, of which the longest is submedian and has a trabant, and the eighth is subterminal and trabanted. The. chromosome with tandem trabants is occasionally found.The karyotype formula follows:K(2n)=24(2b)=2tAsm+2Bst+2Csm+8Dst+2tEst+8Fst where t, sm, and st represent trabant-, submedian-, and subterminal chromosomes, respectively.Sticky chromosome bridges in ana- and telophases in mitotic cells have been met with in the young leaf meristem not infrequently. This irregularity was frequent in the young leaf shoots sprouted early in April, and decreased as the date elapsed and diminished at the end of May.It is suggested that these irregularities caused by the special physiological condition are probably due to cellular inclusions-certain organic substances extractable by water.

Variant Chromosome Numbers in Sphaerocarpos

1. A dwarf and a cupulate male mutant, which developed from spores of pedigreed sporophytes, have in each case a haploid chromosome complement of seven autosomes and one Y chromosome. 2. In harmony with previous results, gametophytes developed from spores of dyads are diploid, or approximately diploid, with (in the cases studied) one X and (usually at least) one Y chromosome. 3. The viable progeny of a triploid sporophyte possess, so far as has been found, no irregular chromosome complements; in each of the clones of such origin studied the diploid autosome number (14) was present. 4. In the cases studied, gametophytic offspring of tetraploid sporophytes are diploid; the males have two Y chromosomes; the apparent females have 2A+X+Y; the latter are probably (in one case certainly) intersexual. 5. Additional viable sporophytic chromosome complements here reported are 4A+X+2Y and 4A+X+3Y, those previously observed being respectively 2A+X+Y, 3A+X+Y, 3A+X+2Y, and 3A+2X+Y.