Showing papers on "Ploidy published in 1974"
TL;DR: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macron nuclei and their kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA.
Abstract: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macronuclei. Micronuclei of Stylonychia mytilus contain 1 600 times as much DNA per haploid genome as E. coli. Most of this DNA is shown to be repetitive. The development of the macronucleus involves, as demonstrated by cytology, only 1/3 of the chromosomes which in a first replication phase are polytenized in probably 5 replication steps and appear as giant chromosomes. At this developmental stage considerable amounts of repetitive DNA are still present in the chromosomes. During the subsequent disintegration phase more than 90% of the DNA are eliminated from the macronucleus anlage. The remainder is further replicated five times and composes the final macronucleus. Since this DNA reassociates with a reaction rate almost identical to an ideal second order reaction its kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA. Macronuclear DNA reassociates with a kinetic complexity of 26 times the kinetic complexity of E. coli DNA (corrected for GC content) which indicates that macronuclear DNA sequences exist at a ploidy level of 4 096 C. We assume that macronuclear DNA may be present only once per haploid genome. In this case it represents only 1.6% of the DNA in micronuclei or 10% of the DNA in the giant chromosome stage.
277 citations
TL;DR: Comparisons of the C-banding of the diploid species T. monococcum, T. speltoides, and T. tauschii with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that T. Speltoide could not be the donor of the B genome to wheat and that T, monoc occum and T, tuschii are the probable donors of the D genomes.
Abstract: The somatic chromosomes of common wheat, Triticum aestivum L (2n = 6x = 42), and those of two of its diploid progenitors and T speltoides, have been individually identified by a Giemsa staining technique In wheat, telocentric chromosomes were used to aid the recognition of individual chromosomes, and an ideogram has been constructed depicting the C-band positions There is no similarity in the C-banding of chromosomes within a homoeologous group, with the possible exception of group 5 Comparisons of the C-banding of the diploid species T monococcum, T speltoides, and T tauschii with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that T speltoides could not be the donor of the B genome to wheat and that T monococcum and T tauschii are the probable donors of the A and D genomes, respectively
235 citations
TL;DR: An approach was made as to how to arrange chromosomes and chromosome segments in their proximity to each other in a model of an internal order in the interphase nucleus in which finally the absolute localization of the chromosomes will be discovered.
Abstract: This paper has two parts. The first one is theoretical, whereas in the second, some experimenteal results are reported.
Part 1: Theoretical Considerations. Comings' considerations on an ordered arrangement of chromatin in the interphase nucleus are used as a basis for further investigations and calculations in order to establish a preliminary model of the interphase nucleus. Information on the amount of DNA of a diploid human nucleus, on the degree of spiralization of chromatin threads found in electron microscopy, and measurements of salivary gland chromosomes was used to estimate the lengths of the entire interphase chromosomes. The number of fixing points-pores—was indirectly calculated proposing a model of an internal order of the chromatin threads. This number was found in concord with a direct calculation of the number of pores in the nuclear membrane based on results from electron microscopy.
Part 2: Experimental Results and Discussion. In the second part of this study, an approach was made as to how to arrange chromosomes and chromosome segments in their proximity to each other. Results of cytogenetic studies of newborn babies and abortions, of cells from patients with Bloom's syndrome and Fanconi's anemia and normal cells treated with Mitomycin C and Trenimon, are thought to be informative under certain suppositions for the problem, which chromosome or chromosome parts are situated in proximity to each other. The symmetrical and equal interchanges seen, for example, in Bloom's syndrome are an indication of somatic pairing during the time of reunion. Therefore, the unequal interchanges in the same syndrome in which different chromosomes are involved should give evidence for proximity of nonhomologous chromosomes. Arguments for and against a temporal and spacial hypothesis for somatic pairing are discussed. The differing frequencies of chromosomes involved in Robertsonian translocations in man are informative for proximities of satellite regions at the nucleolus. Nucleolus and sex chromatin could be used as fixed points in a model of the interphase nucleus in which finally the absolute localization of the chromosomes will be discovered. The discussion points out promising methods for further investigations on the subject and mentions problems which could be attacked if the approach described here leads to a model of internal order in the interphase nucleus.
114 citations
TL;DR: The average mitochondrion in these cells contains four mitochondrial genomes in both the haploid and the diploid, so the effect of nuclear gene dosage on the regulation of mitochondria is assessed.
Abstract: In order to assess the effect of nuclear gene dosage on the regulation of mitochondria we have studied serial sections of a set of isogenic haploid and diploid cells of Saccharomyces cerevisiae, growing exponentially in the absence of catabolite repression, and determined the amount of mitochondrial DNA per cell. Mitochondria accounted for 14% of the cytoplasmic and 12% of the total cellular volume in all cells examined regardless of their ploidy or their apparent stage in the cell cycle. The mean number of mitochondria per cell was 22 in the diploid and 10 in the haploids. The volume distribution appeared unimodal and identical in haploids and diploids. The mitochondrial DNA accounted for 12.6 ± 1.2% and 13.5 ± 1.3% of the total cellular DNA in the diploid and haploid populations, respectively. These values correspond to 3.6 x 10-15 g, 2.2 x 109 daltons, or 44 genomes (50 x 106 daltons each) per haploid and twice that per diploid cell. On this basis, the average mitochondrion in these cells contains four mitochondrial genomes in both the haploid and the diploid.
112 citations
TL;DR: The rate of rejoining of γ-ray induced DNA strand breaks has been measured in diploid skin fibroblasts from normal subjects at early and middle passage through their in vitro lifespan and compared to the rate observed in cells from 4 patients with symptoms of the Hutchinson-Gilford Progeria syndrome of precocious aging.
84 citations
TL;DR: The relative adaptation of isogenic haploid and diploid strains of yeast was investigated in different sets of physiological conditions and results are consistent with the hypothesis that diploids cells are simply double haploids, and diPloidy per se does not confer any direct adaptive advantage.
Abstract: The relative adaptation of isogenic haploid and diploid strains of yeast was investigated in different sets of physiological conditions. When all nutrients were present in excess, no difference in the reproductive rates of isogenic haploid and diploid strains of yeast was detected in both optimal and non-optimal growth conditions. Competition between haploid and diploid strains of yeast was observed when growth was limited by the concentration of a single nutrilite. Under certain conditions when fitness (reproductive rate) is determined by transport of an essential nutrilite that exists in very low concentrations, diploid cells were selected against. These environmental conditions are similar to those found in offshore marine environments where nutrients are often present in extremely low concentrations. The fitness of diploid cells was estimated to be.93 ±.02 (haploid fitness = 1). The reduced fitness of diploid cells in this environment can be explained by the reduced surface area/volume ratio possessed by diploid cells in comparison to haploid cells. The fitnesses of haploid and diploid cells in these environments are closely correlated with geometric variations in these strains. These results are consistent with the hypothesis that diploid cells are simply double haploids, and diploidy per se does not confer any direct adaptive advantage. The mechanism of the evolution of diploidy as a dominant phase in the life cycle of higher plants and animals remains obscure.
75 citations
TL;DR: In hexaploid wheat and diploid rye, different varieties have different numbers of ribosomal RNA genes as indicated by rRNA/DNA hybridisation, but analyses of DNA isolated from substitution lines have indicated that none of the four organiser chromosomes possess an invariant number of riboRNA genes.
Abstract: In hexaploid wheat and diploid rye, different varieties have different numbers of ribosomal RNA genes as indicated by rRNA/DNA hybridisation. Wheat has four different chromosomes which carry nucleolar organisers. Analyses of DNA isolated from substitution lines in which each of these nucleolar organiser chromosomes of several varieties has been substituted one at a time into a common genetic background, have indicated that none of the four organiser chromosomes possess an invariant number of ribosomal RNA genes. The ribosomal RNA gene complement of the varieties investigated can be approximately accounted for by the sum of the ribosomal RNA genes on each of the four nucleolar organiser chromosomes.
74 citations
TL;DR: A comparison of the Giemsa-banding patterns of the X chromosomes in various mammalian species including man indicates that two major bands (A and B), which are resistant to trypsin and urea-treatments, are always present irrespective of the gross morphology of theX chromosomes.
Abstract: A comparison of the Giemsa-banding patterns of the X chromosomes in various mammalian species including man indicates that two major bands (A and B), which are resistant to trypsin and urea-treatments, are always present irrespective of the gross morphology of the X chromosomes. This is true in all mammalian species with the "original or standard type" X chromosomes (5–6% of the haploid genome) thus far analyzed. In the unusually large-sized X chromosomes the extra chromosomal material may be due either to the addition of genetically inert constitutive heterochromatin or to an X-autosome translocation. In these X chromosomes two major bands are present in the actual X-chromosome segment. Our data on C and G band patterns also support Ohno's hypothesis that the mammalian X chromosome is extremely conservative in its genetic content, in spite of its cytogenetic variability.
68 citations
TL;DR: In further studies on DNA from larval diploid tissues, the following findings were made: 1) the Ybb-chromosome carries no rDNA; 2) flies carrying four nucleolus organizers do not tend to lose rDNA, even after eleven generations, and 3) theucleolus organizer on the wild type Y chromosome may have significantly less rDNA than does that on the corresponding X chromosome.
Abstract: The proportion of the Drosophila genome coding for ribosomal RNA was examined in DNA from both diploid and polytene tissues of Drosophila melanogaster by rRNA-DNA hybridization. Measurements were made on larvae with one, two, three and four nucleolus organizer regions per genome. In DNA from diploid tissues the percent rDNA (coding for 28S and 18S ribosomal DNA) was found to be in proportion to the number of nucleolus organizers present. The number of rRNA genes within a nucleolus organizer therefore does not vary in response to changes in the number of nucleolus organizers. On the other hand, in DNA from cells with polytene chromosomes the percent rDNA remained at a level of about 0.1% (two to six times lower than the diploid values), regardless of either the number of nucleolus organizers per genome or whether the nucleolus organizers were carried by the X or Y chromosomes. This independence of polytene rDNA content from the number of nucleolus organizers is presumably due to the autonomous polytenization of this region of the chromosome. When the rDNA content of DNA from whole flies is examined, both the rDNA additivity of the diploid cells and the rDNA independence of polytene cells will affect the results. This is a possible explanation for the relative rDNA increase known to occur in X0 flies, but probably not for the phenomenon of rDNA magnification. — In further studies on DNA from larval diploid tissues, the following findings were made: 1) the Ybb-chromosome carries no rDNA; 2) flies carrying four nucleolus organizers do not tend to lose rDNA, even after eleven generations, and 3) the nucleolus organizer on the wild type Y chromosome may have significantly less rDNA than does that on the corresponding X chromosome.
63 citations
TL;DR: A rapid and simple technique for examining chromosomes of the cellular slime mould Dictyostelium discoideum based on standard cytological techniques involving fixation in methanol/acetic acid and staining with Giemsa stain concludes that aneuploids can divide but that they are unstable and readily lose chromosomes to form aneuPLoids of lower chromosome numbers and eventually haploids.
Abstract: SUMMARY: We have developed a rapid and simple technique for examining chromosomes of the cellular slime mould Dictyostelium discoideum, based on standard cytological techniques involving fixation in methanol/acetic acid and staining with Giemsa stain. The haploid chromosome set is analysed. Four diploid strains are examined cytologically in order to determine their ploidal stability and to determine the pathway of haploidization in the parasexual cycle. In the absence of cloning, diploid strains eventually revert to haploid. Haploidization proceeds via transient aneuploidy. Aneuploids of all classes, n+1 through to 2n+2, have been demonstrated cytologically. It is concluded that aneuploids can divide but that they are unstable and readily lose chromosomes to form aneuploids of lower chromosome numbers and eventually haploids. Hence, the process of haploidization is similar to that found in the parasexual cycle of Aspergillus nidulans.
59 citations
TL;DR: Analysis of the segregation of the mating type alleles and other markers on chromosome III indicates that the primary event which leads to the bisexual phenotype is the loss of one homolog of chromosome III during vegetative growth to produce a monosomic (2n-1) diploid.
Abstract: A diploid strain of Saccharomyces cerevisiae has been isolated which exhabits bisexual mating behavior. The strain mates with either a or alpha strains with a relative mating efficiency of 1 to 2%. The efficiency of mating is correlated with the frequency with which subclones of this strain revert to a single mating type. Crosses of the bisexual diploid with a/a or alpha/alpha diploids yield bisexual segregants with a frequency of approximately 3%. Analysis of the segregation of the mating type alleles and other markers on chromosome III indicates that the primary event which leads to the bisexual phenotype is the loss of one homolog of chromosome III during vegetative growth to produce a monosomic (2n-1) diploid. Evidence is presented that the loss of chromosome III and possibly of other chromosomes during vegetative growth is affected by a recessive nuclear gene-her (hermaphrodite)-which is not closely linked to the mating type locus.
TL;DR: In acetocarmine root-tip squashes, diploid cells of Ornithogalum virens in prophase exhibit configurations resulting from end-to-end associations of the six chromosomes.
Abstract: In acetocarmine root-tip squashes, diploid cells of Ornithogalum virens in prophase exhibit configurations resulting from end-to-end associations of the six chromosomes. Homologues lie opposite one...
01 Jan 1974
TL;DR: Cultivated barley, Hordeum vulgare L., is one of the leading experimental organisms in genetic studies of flowering plants, and many of these characters have occurred as mutants after physical- or chemical-mutagen treatments.
Abstract: Cultivated barley, Hordeum vulgare L., is one of the leading experimental organisms in genetic studies of flowering plants. The wide use of this important agricultural crop plant in genetic studies may be attributed to its diploid nature, low chromosome number (2n = 14), world-wide distribution, high degree of self-fertility, ease of hybridization, relatively large chromosomes which allow detection of several kinds of chromosome aberrations, and numerous easily classified hereditary characters. Many of these characters have occurred as mutants after physical- or chemical-mutagen treatments. Since barley is one of the chief models among higher plants for induced-mutation studies, new characters are being added at a considerable rate.
TL;DR: Findings suggest the involvement of regulatory mechanisms controlling isozyme activity in polyploid series of fern gametophytes and sporophytes suggest that increases and decreases in individual isozymes as ploidy increased.
Abstract: Total soluble proteins, peroxidase, and peroxidase isozymes were examined in polyploid series of fern gametophytes and sporophytes. A distinctive pattern of protein bands was associated with gametophytes and sporophytes and the pattern did not vary within each phenotype with increases in the genome. Peroxidase activity per cell increased in direct proportion to increases in the genome and was determined to be gene dosage related. Slight differences in the patterns of peroxidase isozyme bands were associated with increases in the chromosome complement in both series of plants, but major variations were found between gametophyte and sporophyte. Quantitative analysis of peroxidase activity in each band revealed both increases and decreases in individual isozymes as ploidy increased. These findings suggest the involvement of regulatory mechanisms controlling isozyme activity.
TL;DR: Both breeding systems and ploidy levels show that the direction of the change has been from x=5 to x=4 by a translocation of the Robertsonian type, suggesting a Robertsonian relationship between these plants.
Abstract: The plant species Gibasis schiedeana (Kunth) D. R. Hunt sens. lat. contains two cytotypes viz. a self-sterile diploid with 2n=10 (x=5) and a selffertile cytological autotetraploid with 2n=16 (x=4). Single chromosome sets of these plants consist of 2 metacentrics +3 acrocentrics, and 3 metacentrics +1 acrocentric chromosomes respectively suggesting a Robertsonian relationship between them. Their artificial F1 hybrids show the pairing of acrocentrics with metacentric arms confirming the supposed nature of the chromosome affinities. Both breeding systems and ploidy levels show that the direction of the change has been from x=5 to x=4 by a translocation of the Robertsonian type.
TL;DR: Centromeric heterohromatin as revealed by the Giemsa BSG technique has been quantitatively analyzed in giant versus diploid trophoblast nuclei, and a constant ratio of chromocenter area: total nuclear area in giant cells is observed.
Abstract: Giant trophoblast nuclei of the mouse and the rat, known to contain hundreds, or even thousands, of times the haploid amount of DNA, have been studied by a number of cytological techniques. These nuclei appear in two morphological states:“reticulate,” in which large numbers of chromatin threads of uniform size intermingle throughout the nucleus, often radiating from clumps of heterochromatin adjacent to the nucleoli, and “homogeneous,” in which the chromatin is more evenly dispersed and individual threads are more difficult to distinguish. Intermediate morphologies are also observed. In neither case were structures resembling polytene chromosomes discernible. — Centromeric heterohromatin as revealed by the Giemsa BSG technique has been quantitatively analyzed in giant versus diploid trophoblast nuclei. Although the median number of chromocenters is slightly greater in giant than in diploid nuclei, the range is similar. In both cases, the chromocenter number is usually less than the diploid number of chromosome pairs, indicating the attraction between centromeres not only of homologous, but also of heterologous, chromosomes. By scanning microdensitometry, we have observed a constant ratio of chromocenter area: total nuclear area in giant cells. This ratio, which likely reflects the ratio of chromocenter volume: total nuclear volume, is in good agreement with that of satellite DNA: total DNA.
TL;DR: The distribution of heterochromatic regions in the chromosomes of diploid, tetraploid and hexaploid wheat showed that the B genome possesses characteristic large blocks as discussed by the authors.
Abstract: The distribution of heterochromatic regions in the chromosomes of diploid, tetraploid and hexaploid wheat shows that the B genome possesses characteristic large blocks. Though analyses of probable B genome donors indicate that Aegilops speltoides has a pattern of distribution of heterochromatin nearest to the B genome chromosomes, a polyphyletic origin of tetraploid wheat seems more plausible.
TL;DR: Interspecific hybridization in the homosporous ferns usually results in the formation of sterile diploid or triploid hybrids; this type of hybridization is accompanied usually by the meiotic production of unreduced spores by the sterile hybrid; these spores have the potential to produce polyploid derivatives of the hybrid that have the ability to reproduce through normal sexual processes.
Abstract: Interspecific hybridization in the homosporous ferns usually results in the formation of sterile diploid or triploid hybrids. Sterility in these instances is the result of extreme differences in chromosome homologies between the parental taxa and the subsequent lack of normal chromosome pairing in the hybrids. Hickok and Klekowski (1973) have demonstrated that this type of hybridization is accompanied usually by the meiotic production of unreduced spores by the sterile hybrid; these spores have the potential to produce polyploid derivatives of the hybrid (allopolyploids) that have the ability to reproduce through normal sexual processes. Through this process, reticulate evolution of the type documented by Manton and Walker (1953) and Walker (1955, 1961) inDryopteris and by Wagner (1954) in Asplenium can be seen to be a major feature in the evolution of homosporous ferns. A notable exception to this production of sterile hybrids and fertile polyploid offspring in the ferns was documented by Walker (1958) in Pteris where hybridization between P. quadriaurita and P. multiaurita resulted in the formation of completely fertile F1 diploid hybrids that exhibited complete bivalent formation at meiotic prophase. The subsequent production of F2 segregates and backcross hybrids to parental types resulted in the production of a hybrid swarm in which all of the taxonomic
TL;DR: Data is presented that indicates the feasibility of attaining the five objectives outlined in the introduction of laser microirradiation, which are to determine which chromosomes and chromosome regions are essential for immediate cell survival, assign genes to specific chromosome regions, and study the repair of chromosomal damage caused by laser irradiation.
Abstract: In this article I have presented data that indicate the feasibility of attaining the five objectives outlined in the introduction. It should be possible to assign genes to specific chromosome regions by (i) selective DNA deletion of a 0.25- to 0.5-µ.m segment of one or both homologous chromosomes, (ii) deletion of one or both entire homologous chromosomes, or (iii) combining cell fusion with selective deletion of whole chromosomes and then deletion of chromosome segments.
By laser microirradiation it should be possible to determine which chromosomes and chromosome regions are essential for immediate cell survival by removing from individual cells whole chromosomes, and chromosome segments from each of the chromosomes in the karyotype, and then assessing the cloning efficiency of each cell. For example, we have already determined that removal of one large chromosome No. 1 from PTK2 cells does not prevent the cell from undergoing a subsequent mitosis.
It should also be possible to generate new classes of mutants by damaging small selected areas of DNA with the laser beam and then cloning the irradiated cells—but this has yet to be demonstrated. This procedure might reveal recessive alleles on the nonirradiated homolog, or might result in the direct production of a genetic mutation. Irradiation of identical places on both homologous chromosomes could result in deletion of a genetic locus which ultimately might be detected as a deficiency in a metabolic pathway or some other cellular abnormality.
Studies on chromosome stability and DNA constancy can be conducted with laser irradiated cells. For example, the karyotypic analysis of chromosome No. 1 suggests that a cellular mechanism exists to maintain the constancy of this chromosome in both the diploid and tetraploid cell lines. The same approach could be used with each of the chromosomes in the karyotype. Various cytochemical procedures could be used for making quantitative DNA studies of the cells, and chromosome and DNA analyses could be performed at varying times following laser microirradiation.
It might also be possible to study the repair of chromosomal damage caused by laser irradiation. The cells could be examined by autoradiographic, cytochemical, and electron microscopy procedures at varying times after irradiation, and because the precise location, time, and nature of the mutational event would be known, subsequent analysis of repair and alteration would be facilitated.
TL;DR: Of fundamental importance is the issue of whether the sex-determining mechanism in birds is ZZ(d)-ZO(9) or ZZ-ZW(9), and whether the diploid numbers would differ by one chromosome between the sexes.
Abstract: It is some 70 years since man first attempted to describe the chromosome complement of an avian nucleus (Loyez 1906). Only in the last 10 to 12 years has any significant progress been made toward achieving accurate karyotypes. Even so, there is still today some uncertainty about exact diploid numbers for avian species. The major reason for this is simply that bird chromosomes are numerous (range = 52-92) and range in size from 6 to 10 micra to barely visible by light microscopy. Of fundamental importance is the issue of whether the sex-determining mechanism in birds is ZZ(d)-ZO(9) or ZZ(d)-ZW(9). This is important because in the former case diploid numbers would differ by one chromosome between the sexes, and the possible genetic contribution of an additional chromosome, perhaps sex-determining, would be totally ignored. Interestingly, some of the very first reports on bird chromosomes were aimed at harmonizing the results of genetic studies in chickens (showing female heterozygosity for sex and sexlinked factors) with cytological data (Guyer 1916). The concept of an XX(d)-XO(9) sex chromosome mechanism soon developed. Unfortunately, the wrong chromosome, No. 1, was considered the X in Gallus domesticus.
TL;DR: The diploid species that donated the A and D genomes to the polyploid wheats have been recognized for some time and new evidence indicates that Triticum speltoides cannot be the B genome donor to T. turgidum or T. aestivum.
Abstract: The diploid species that donated the A and D genomes to the polyploid wheats have been recognized for some time. New evidence indicates that Triticum speltoides cannot be the B genome donor to T. turgidum or T. aestivum. T. speltoides is probably homologous to the G genome of T. timopheevii. The donor of the B genome to T. turgidum and T. aestivum is currently unrecognized.
TL;DR: There was no correlation between the duration of meiosis and the amount of homoeologous chromosome pairing, and some doubt must be cast upon the idea that the time available for pairing is limiting to the pairing process.
Abstract: In order to investigate the possible relation between meiotic time and meiotic chromosome pairing behaviour, meiosis was timed in various forms of wheat and wheat hybrids. First, meiosis was timed in ten Triticum aestivum (var. Chinese Spring) genotypes with different chromosome constitutions which differed widely in the meiotic pairing behaviour. Secondly, in order to escape from the disadvantage of aneuploid material, meiosis was also timed in plants which differed in the extent of homoeologous pairing because of the activities of different alleles at one or two loci. For this experiment use was made of F 1 -hybrids from the cross T. aestivum x Aegilops mutica which, although they all have 28 chromosomes, differ widely in the amount of homoeologous pairing. Thirdly, meiosis was also timed in 28-chromosome and 29-chromosome plants derived from the cross between rye (Secale cereale) x 43-chromosome T. aestivum containing a single Ae. mutica addition chromosome known to carry genes which greatly affect the level of homoeologous pairing in wheat. Although the 28-chromosome plants display very little pairing (chiasma frequency per cell (c. f.) = 0.5) while 29-chromosome plants display a much higher amount of pairing (c. f. = 7.8) no difference in meiotic time was detected between them. Similarly, the duration of meiosis was not significantly different between the three types of F 1 -hybrids between T. aestivum x Ae. mutica which had chiasma frequencies of 14.3, 7.4 and 0.9. Thus, these results agree in showing that there was no correlation between the duration of meiosis and the amount of homoeologous chromosome pairing. The results obtained for genotypes of Chinese Spring also provided no evidence to support the notion that there is a relation between the level of chromosome pairing and the duration of the pairing process. Consequently some doubt must be cast upon the idea that the time available for pairing is limiting to the pairing process. It was shown that individual wheat chromosomes in Chinese Spring differed in their effects on meiotic duration. For instance, the absence of chromosome 7B has no detectable effect on meiotic duration. The absence of chromosome 5B in two genotypes resulted in an increase in meiotic time from that found in euploid plants (24 h) to that found in tetraploid wheat species (about 30 h). By using plants ditelosomic for chromosome 5B L it was shown that most, if not all, of the genetic effects of chromosome 5B on meiotic time are determined by the short arm.
TL;DR: Three doubled haploid lines artificially derived from each of the burley tobacco varieties, Burley 21, Ky 10, and Harrow Velvet, were compared with the normal diploid lines in 1971 and it was assumed that the genetic variation among the entries was due to the mutation occurred in haploid stage.
Abstract: Three doubled haploid lines artificially derived from each of the burley tobacco varieties, Burley 21, Ky 10, and Harrow Velvet, were compared with the normal diploid lines in 1971. Some of the doubled haploid lines were gene-tically different from the normal diploid lines. At least, three out of the nine doubled hap-loid lines showed the reduced vigor, resulting in the lower yield than the normal diploids. However, none of the doubled haploid lines was higher than the normal diploids in yield. An experimental line, DH-6, derived from Ky 10 variety had an apparently higher leaf number than that of the parental variety. These results were ascertained by the experi-ments in the next year. From the comparison of clonally related doubled haploid lines, it was assumed that the genetic variation among the entries was due to the mutation occurred in haploid stage.
TL;DR: The hypothesis that two major genes control total alkaloid production in burley tobacco is supported, and the feasibility of using the anther-derived haploid technique for the development of tobacco breeding lines is demonstrated.
Abstract: A large population of haploid plants was obtained from the F hybrid ‘LA Burley 21’ ✕ ‘Burley 21’ using an anther culture technique. LA Burley 21 is homoyzgous recessive (aabb) for total alkaloid content, and Burley 21 is homozygous dominant (AABB). Haploid genotypes for alkaloid content included AB, Ab, aB, and ab, obtained from the diploid F hybrid of genotype AaBb. The haploid plants were verified cytologically, and individual haploids were chromosomally doubled by either root or leaf tissue culture procedures to recover the four homozygous doubled haploid forms. The two parental genotypes (AABB and aabb) and the low-intermediate (aaBB) and high-intermediate (AAbb) genotypes were evaluated for stability and compared with conventionally derived alkaloid lines. Haploid plants were extracted from doubled haploid genotypes to obtain additional evidence on stability of anther-derived haploids. The haploids and their derivatives behave as stable true-breeding genotypes. The evidence presented supports the hypothesis that two major genes control total alkaloid production in burley tobacco. The feasibility of using the anther-derived haploid technique for the development of tobacco breeding lines is demonstrated.
TL;DR: The final element necessary to establish the existence of a parasexual cycle in Dictyostelium discoideum has thus been demonstrated.
Abstract: SUMMARY: The genes conferring white fruiting bodies (whi), growth-temperature sensitivity in strain x9 (tsgD12) and resistance to methanol or acriflavine (acrA1) are linked in a group designated chromosome II. A gene, present in strain ax2 and involved in the ability of this strain to grow axenically (axe2), has also been located on chromosome II. An analysis of diploid strains derived from a diploid initially heterozygous for all known genes of chromosome II has revealed that mitotic crossing-over occurs during the vegetative growth of diploid cells. An analysis of the classes of diploid thus isolated leads to a provisional ordering of the genes on chromosome II: centromere, whi, axe2, tsgD12, acrA1. The final element necessary to establish the existence of a parasexual cycle in Dictyostelium discoideum has thus been demonstrated.
TL;DR: Lesch-Nyhan fibroblasts and normal human leukocytes with different glucose-6-phosphate dehydrogenase genotypes were fused by Sendai virus.
Abstract: Lesch-Nyhan fibroblasts and normal human leukocytes with different glucose-6-phosphate dehydrogenase genotypes were fused by Sendai virus. Clones were isolated on the basis of their resistance to a medium containing hypoxanthine, amethopterin, and thymidine and ability to proliferate in monolayer culture. These mononuclear cells (1) incorporated [3H]hypoxanthine, (2) expressed the glucose-6-phosphate dehydrogenase heteropolymer, and (3) were polyploid. Therefore, hybrids can originate from the fusion of two diploid human cells. X chromosome inactivation did not occur in these hybrid cells of male origin. The hybrids expressed both parental genomes and exhibited the senescence and contact feeding characteristic of the human skin fibroblast.
TL;DR: In tissue cultures of male Microtus agrestis, diploid mitoses with two X or two Y chromosomes were found and autoradiographic studies of tetraploid tripolar mitoses showed that the diploids daughter nuclei contain either XX or YY in the male; in the female, X1X1 and X2X2 cells were found less frequently.
Abstract: In tissue cultures of male Microtus agrestis, diploid mitoses with two X or two Y chromosomes were found. For identifiying the sex chromosomes in nonhypotonioally treated mitoses, the asynchrony of DNA replication of the sex chromosomes of both sexes was used. The constitutive heterochromatin of Y replicates later in the S period than X, and X2 of the female replicates later than X1. Autoradiographic studies of tetraploid tripolar mitoses showed that the diploid daughter nuclei contain either XX or YY in the male; in the female, X1X2 daughter nuclei were found less frequently than X1X1 and X2X2 cells.
TL;DR: Low concentrations of the antibiotic griseofulvin were found to cause increased frequencies of somatic segregation due to chromosome nondisjunction in a diploid strain of Aspergillus nidulans.
Abstract: Low concentrations of the antibiotic griseofulvin were found to cause increased frequencies of somatic segregation due to chromosome nondisjunction in a diploid strain of Aspergillus nidulans .
TL;DR: A comparison has been made of the amount of DNA coding for ribosomal RNA present in a polyploid series of plants of Datura innoxia, which were produced by in vitro culture of pollen grains and the data compared with that available from other series of plant of different DNA content or ploidy.
Abstract: A comparison has been made of the amount of DNA coding for ribosomal RNA present in a polyploid series of plants of Datura innoxia. The plants which were produced by in vitro culture of pollen grains were haploid, diploid, triploid, tetraploid and hexaploid. In all instances there was a similar proportion of DNA coding for ribosomal RNA. The implications of these results are discussed, and the data compared with that available from other series of plants of different DNA content or ploidy.