Division Of Meiosis Research Articles

MISDIVISION OF AN AGROPYRON CHROMOSOME

Agrotricum lines, in which an Agropyron chromosome with genes for stem- and leaf-rust resistance replaced wheat chromosome 6D, have been used in breeding programs at the University of Nebraska-Lincoln. The 42-chromosome Agrotricum lines were developed by an initial cross between common wheat (Triticum aestivum) and Agropyron elongatum (2n = 70), followed by backcrosses to various wheat cultivars. These lines were crossed as male parents with Chinese Spring monosomic 6D as female, to obtain plants monosomic for the Agropyron chromosome (20″ + 1′Ag). Microsporocytes in these monosomic alien substitution plants were examined at the first and second divisions of meiosis. The Agropyron chromosome is a small, nearly isobrachial chromosome. It misdivided in 40.1% of the cells at the first division (AI-TI). Meiotic configurations of the misdividing chromosome indicated that the centromere of the Agropyron chromosome is divisible into four functional units (telocentrics) at the first division. Only 11.6% of the cells with lagging chromosomes showed misdivision at the second division (AII-TII) of meiosis. The expected frequency of micronuclei from AII-TII data was compared with that observed at the quartet stage. It was concluded that 24% of the lagging whole or telocentric chromosomes were included in the second division nuclei, indicating that some of the telocentrics may be transmitted. The relatively high rate of misdivision of the Agropyron chromosome considerably increases the chances of recovering telo- and isosomic lines for each arm. Rust tests of these lines will provide evidence for the locations of genes for stem- and leaf-rust resistance on specific arms of this chromosome.

ELECTRON MICROSCOPE OBSERVATIONS OF TELOPHASE II IN THE FLORIDEOPHYCEAE1

SUMMARYTetrahedral tetrasporangia of several florideophycean red, algae were examined with the electron microscope for details of meiosis. Only telophase II nuclei are described since earlier stages were not, observed. Both divisions of meiosis are presumed to occur within the confines of the original tetrasporangial mother cell nuclear envelope. Four nuclei are then formed simultaneously. These observations essentially support Yamanouchi's description of telophase II in Polysiphonia flexicaulis (Harvey) Collins (as P. violacea) and suggest that meiosis in these algae could be basically similar to “uninuclear meiosis” in the fungi Saprolegnia and Saccharomyces.

Origin of extragonadal teratomas and endodermal sinus tumours.

TERATOMAS are usually differentiated tumours, containing tissues derived from ectoderm, endoderm and mesoderm, and may arise in the gonads or elsewhere. Benign ovarian teratomas are parthenogenetic tumours derived from a single germ cell after the first division of meiosis, as studies of chromosome markers and enzyme variants have shown1,2. We have now found that extragonadal teratomas develop in a different manner. We have examined single gene products and chromosomes in extragonadal teratomas and report here our results. We include data on endodermal sinus tumours because of their similarity to teratomas3,4.

Conditional mutants of meiosis in yeast.

Three temperature-sensitive mutants, spo1-1, spo2-1, and spo3-1, were characterized with respect to their behavior in sporulation medium at a restrictive temperature. The time of expression of the functions defective in the mutants was determined by temperature-shift experiments during the sporulation process. In addition, each mutant was examined for the following: (i) its ability to undergo the nuclear divisions of meiosis; (ii) deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein synthesis; (iii) protein turnover; and (iv) colony-forming ability after exposure to sporulation medium. Mutant spo1-1 is defective in a function which confers a temperature-sensitive period which extends over 32% of the sporulation cycle. The temperature-sensitive period of mutant spo2-1 occupies 34% of the cycle, whereas the temperature-sensitive period of mutant spo3-1 extends over 2% of the sporulation cycle. Cytological evidence indicates that all three mutants initiate but do not complete the meiotic nuclear divisions. The DNA content of sporulation cultures of mutants spo1-1 and spo3-1 did not increase to the wild-type level; DNA synthesis in spo2-1 was normal. All three strains exhibit a loss of colony-forming ability during incubation in sporulation medium at the restrictive temperature. RNA and protein synthesis and protein turnover occur in the mutants.

Investigations into causes of sterility IV. Gametocide-induced male-sterilePhaseolus aureus Roxb.

Phaseolus aureus Roxn, cultivar T51 was treated with aqueous foliar sprays of 0.01, 0.025% and 0.05% 2,2-dichloropropionic acid (DPA) just before the initiation of floral buds when the plants were 25 days old. Flower buds were fixed 10 days after treatment. The plants in the two latter treatments were 100% pollen sterile. Meiosis in these treatments was characterized by multivalent associations at diakinesis and metaphase I. These associations were found to be due to stickiness, produced by agglutination of chromatin. Both the divisions of meiosis were characterized by sticky chromosome bridges and laggards, resulting in the formation of micronuclei and consequently polysporads. Histology of anthers revealed a vagary in the behaviour of the tapetum.

MICROSPECTROPHOTOMETRIC MEASUREMENT OF NUCLEAR DEOXYRIBONUCLEIC ACID CONTENT IN TWO MYXOMYCETES

Spore formation in Didymium iridis (Ditmar) Fries and Didymium nigripes (Link) Fries is generally preceded by both divisions of meiosis in the developing sporangium, and at the time of cleavage the spores are haploid with the 1C deoxyribonucleic acid (DNA) content. Synthesis of DNA begins soon after spore delimitation and the mature spores are in the haploid 2C category.The plasmodial nuclei were found to have twice the DNA content of the myxamoebae and the mature spores, hence karyogamy must precede plasmodial formation. The myxamoebal and plasmodial nuclei appear to have a very rapid rate of DNA synthesis, with an extended G2 phase of development; consequently myxamoebae are generally in the haploid 2C category and the plasmodial nuclei in the diploid 4C category.In D. iridis the opposite mating types have different amounts of nuclear DNA, and the arithmetical sum of the mean DNA content of the mating types is equal to the mean DNA content of the plasmodial nuclei.In D. nigripes grown on a medium containing 2% w/v glucose a large percentage of uninucleate amoeboid cells have a DNA content equal to that of the plasmodial nuclei. These cells are presumed to be zygotes.

Chromosomes of Some Archaeopulmonata (Mollusca: Basommatophora)

This paper presents the chromosome numbers of 7 species of primitive basommatophoran snails and discusses these numbers in relation to systematics and to those numbers reliably reported for the Archaeopulmonata by other authors.1. Sixteen bivalents were observed in cells of the first division of meiosis in the 4 species of Siphonariidae studied, Siphonaria alternata, S. guamensis, S. laciniosa and S. pectinata.2. Several different chromosome numbers were observed in the two species of Ellobiidae studied. Seventeen bivalents were observed in Cassidula vespertilionis and 19 pairs of chromosomes were found in Melampus coffeus and in a population (of hybrids?) resembling this species but differing slightly on shell morphology. One specimen in this latter population was a tetraploid individual with 38 bivalents.3. The one species of Chilinidae examined, Chilina fluviatilis, had 18 pairs of chromosomes.4. The caryotype of Melampus bidentatus lineatus consists of 7 pairs of metacentric chromosomes and 11 pairs of submetacentric chromosomes. This is the first accurate report of the caryotype of an ellobiid snail.

Contribution to the Cytology of Hymenomycetes. VII. Karyological Studies inFomes LividusKalchbr

SUMMARY1. The karyological phenomena in the life-cycle of Fomes lividus Kalchbr., a resupinate member of the family Polyporaceae has been studied in detail.2. The young basidium is distinctly binucleate. This dikaryotic condition comes to an end with their fusion to form a synkaryon. The synkaryon first undergoes an interphasic enlargement followed by the appearance of chromatic materials as reticulate structure. Subsequently, from the reticulum typical chromosomes (2 n = 6) are formed. A haploid chromosome set constituting a genome (n = 3) forms a daughter nucleus at each pole. The orientation of the spindle of the first division of meiosis (heterotypic) is more or less transverse while in the second division (homotypic) it shows irregularities. A third nuclear division occurs forming the eight nucleate condition of the basidium. Four of these eight nuclei migrate into four developing basidiospores while the other four degenerate in the collapsing basidium. The nucleus within the basidiospore often divid...

Asynapsis in a Tetraploid Forage sorghum

Asynapsis was found to be associated with a recessive dwarf character in progeny derived from hybrids between Sorghum almum Parodi and perennial sweet Sudan grass. The average number of univalents at first metaphase varied from 1.5 to 38.4 per cell in the 10 plants examined. Lagging univalents usually divided or misdivided at first anaphase or telophase. In plants with a very small average number of bivalents at first metaphase, the second division of meiosis rarely occurred and the pollen grains were formed from the products of the first division. All pollen grains degenerated and the asynaptic plants were sterile.

LINKAGE IN AUTOTETRAPLOID MAIZE

bivalent and, since four potential gametes result from each meiosis, these strands pass to different gametes and may, genetically, be dealt with separately. The only concern, therefore, is with the proportioris of each type of strand resulting from crossing-over and their possible combinations in the zygotes. Allopolyploids, such as wheat, show the same general type of genetical behavior since multivalent formation is rare. In autopolyploids, on the other hand, more than four chromatids are concerned in the formation of the various configurations which occur at the first division of meiosis, and, since there are still only four gametes formed, each gamete receives more than one strand from each configuration. Hence with autopolyploids there is the additional consideration of the ways in which the chromatids may be combined in the gametes themselves. This leads to a number of complications in the analysis of linkage in autopolyploids. MULLER (1914) calculated the monofactorial segregations to be expected from autotetraploids if the two chromatids of each chromosome acted as one at the first meiotic division, and HALDANE (1930) extended the work to include several higher autopolyploids. This mode of inheritance is called chromosome segregation. HALDANE (1930) also established the segregations to be expected if the two chromatids from each chromosome acted entirely independently of one another. Random chromatid segregation is the term applied to this method. SOMME (1930) reported some linkage studies in autotetraploid Primula sinensis and DE WINTON and HALDANE (1931) in a more comprehensive investigation of the subject, using the same plant, gave the linkage formulae applicable to the chromosome type of segregation. SANSOME (1933), working with the tomato, presented the corresponding linkage formulae on the basis of random chromatid segregation. In addition to these cases of linkage studies in autopolyploid plants, investigations on crossing-over in triploid Drosophila melanogaster have been reported by BRIDGES and ANDERSON (1925) and REDFIELD (1930, 1932). Later workers ( MATHER 1936) have recognized that these segregation and linkage expectations are in the nature of limiting types, and that the true segregations to be expected TF irst division of meiosis four chromatids take part in the formation of each

Contribution to the Cytology of Hymenomycetes. VI. Karyological Studies inFlammula DilepisB. & Br.

SUMMARY1. The karyological cycle in the life-history of Flammula dilepis, brown-spored member of the family Agaricaceae, has been studied in detail.2. Young binucleate basidia are the dilated hyphal tips, each having a simple clamp-connexion at the base. This dicaryotic condition comes to an end with the fusion of these two nuclei of a basidium forming a synkaryon. This synkaryon then enlarges and ultimately undergoes reduction division (heterotypic). With the onset of prophase, chromosomes make their appearance and during metaphase 6 clear bivalents are evident (2 n = 12). Bivalents then separate and the two sets form two daughter nuclei, each with 6 chromosomes. The second division is homotypic and the four daughter nuclei thus formed also contain six chromosomes (n = 6) each. The orientation of the spindle in the first division of meiosis is always transverse, while it is irregular during the second division. The four daughter nuclei then migrate into the four developing basidiospores through the steri...

THE ASSOCIATION OF A SINGLE B‐CHROMOSOME WITH MALE STERILITY IN PLANTAGO CORONOPUS

Paliwal, Ripsudan L. (B. R. College, Agra, India.), and Beal B. Hyde. The association of a single B‐chromosome with male sterility in Plantago coronopus. Amer. Jour. Bot. 46(6): 460–466. Illus. 1959.—Two species of Plantago showing male sterility have been studied cytogenetically. In P. ovata (n=4) the sterility appears to be cytoplasmic. In P. coronopus (n=5) all male‐sterile plants contain a single extra chromosome which is largely heterochromatic, shorter, and not homologous with any of the other chromosomes. No male‐fertile plants contain this B‐chromosome. Meiosis is regular in the male‐sterile lines. The accessory chromosome usually does not divide and moves to one pole at the first division of meiosis and divides regularly in the second division. Degeneration of all microspores occurs before pollen mitosis. Male‐sterile plants are apomictic, but whether or not male‐fertile plants are also apomictic has not yet been determined.

The Association of a Single B-Chromosome with Male Sterility in Plantago Coronopus

Paliwal, Ripsudan L. (B. R. College, Agra, India.), and Beal B. Hyde. The association of a single B-chromosome with male sterility in Plantago coronopus. Amer. Jour. Bot. 46(6): 460–466. Illus. 1959.—Two species of Plantago showing male sterility have been studied cytogenetically. In P. ovata (n=4) the sterility appears to be cytoplasmic. In P. coronopus (n=5) all male-sterile plants contain a single extra chromosome which is largely heterochromatic, shorter, and not homologous with any of the other chromosomes. No male-fertile plants contain this B-chromosome. Meiosis is regular in the male-sterile lines. The accessory chromosome usually does not divide and moves to one pole at the first division of meiosis and divides regularly in the second division. Degeneration of all microspores occurs before pollen mitosis. Male-sterile plants are apomictic, but whether or not male-fertile plants are also apomictic has not yet been determined.

Nuclear behaviour in the cultivated mushroom.

1. The number of nuclei found in the hyphal cells was found to vary between 1 and 36, with a mean at 6.44±0.08. In contrast with this variability the cells of the hymenium were always found to be initially binucleate. This reduction in nuclear number in the hymenial tissue is attributed to a number of factors. 2. Evidence for the heterozygous nature of the fusion nucleus was obtained from a study of chromosome bridges at Anaphase I and II of meiosis. This accords with the genetical results of other investigators who have shown that segregation of a number of factors occurs at meiosis. 3. Clamp connections and conjugate mitotic spindles were not observed although nuclear migration between cells was found to occur. It is suggested that this migration may provide an opportunity for maintaining a genetic balance between cells. 4. It was found that the resting nuclei could attain one of two resting conditions, the expanded or the homogeneous state, which were characterised by differences in staining affinity. It was shown that the different resting states were not the result of genetical differences between nuclei and did not represent different stages of the mitotic cycle. From observations on the development of the young basidium and on the distribution of these two nuclear types, it is suggested that the difference between the resting nuclei is primarily associated with a difference in cellular activity, the homogeneous resting nuclei characterising cells in active metabolic states. 5. The haploid chromosome number was found to be n = 12, a determination which differs from previously recorded numbers, and the 24 chromosomes of the fusion nucleus regularly formed 12 bivalents at meiosis. The presence of laggard chromosomes at meiosis and mitosis was attributed to sticky adhesions between heterochromatic regions of the chromosomes. 6. Contrary to the reports of previous investigators, centrosomes were not observed at meiosis or mitosis. Observations made on other Basidiomycetes and reports by other investigators suggest that the absence of centrosomes may be a characteristic of the group. 7. Differences in the manner of alignment of the spindles at the second division of meiosis were found between basidia. It was shown that the nuclear constitution of the basidiospores depended upon the type of spindle alignment, and a bias towards the production of spores containing non-sister nuclei was found. It is pointed out that the production of an excess of spores containing non-sister nuclei serves to maintain a high degree of heterokaryosis without involving nuclear exchange between plants.

The Chromosomes of <i>Dicranocephalus agilis</i> (Hemiptera: Heteroptera)

1. The chromosome number in the males of Dicranocephalus agilis is 2n=14. The complement includes a pair of m-chromosomes and a pair of sub-equal sex chromosomes.2. The first division of meiosis is reductional for the differential regions of the autosomes and for the m-chromosomes which are completely differential. It is equational with respect of the sex chromosomes.3. The sex chromosomes are positively heteropycnotic at the prophase of meiosis I and are associated non-homologously. They are double when the autosomes pair at zygotene.4. At metaphase of first and second division the autosomes congress to form a ring on the periphery of the spindle. This is in keeping with their size, valency and the space available.5. At equilibrium, the sex chromosomes auto-orientate side by side in the ring with the autosomes at first metaphase. The sex pseudo-bivalent congresses in the centre of the spindle at second metaphase where less space is available.6. The sex chromosomes become negatively heteropycnotic at first metaphase and the sex chromatids form a pseudo-bivalent during their anaphase separation. This is facilitated by their side by side orientation at metaphase (a consequence of their earlier association), their convergence as they approach the poles and their reduced repulsion.7. The early formation of the sex pseudo-bivalednt in D. agilis and Oncopeltus fasciatus is considered adaptive in the absence of an interphase which suggests a more rapid division than in Cimex and Oncopeltus nigriceps where the pseudo-obivalent forms later and the second division is of longer duration.8. The m-chromosomes are unpaired at prophase of the first division but associate in the centre of the spindle at first metaphase when they are understained. They congress to the centre of the spindle at second division also. They, and the sex chromosomes remain understained until the completion of meiosis.9. The differential staining of the sex and in-chromosomes compared with the autosomes is important only in that it provides a visible demonstration of allocycly which can be inferred on other grounds.10. The centromere in D. agilis is diffuse. It is suggested that the time and place at which the chromosomal spindle fibres are organised are partly responsible for determining whether the first division of meiosis is reductional for the differential segments (as is general in the Heteroptera) or equational (as is generally the case in the Homoptera).

Use of Tetratype Frequencies for estimating Spindle Overlapping at the Second Division of Meiosis in ‘Ordered’ Tetrads

WITH ordered tetrads, such as occur in the asci of Neurospora crassa, the second-division meiotic spindles do not overlap (Fig. 1a) and the subsequent mitotic spindles are also well separated, with the result that analysis of the sequence of spores within the ascus allows a distinction to be made between first- and second-division segregation for a particular pair of alleles. With unordered tetrads, second-division segregation frequencies can be calculated from the frequencies of tetratype tetrads (for example, AB, ab, Ab, aB) for three independent loci, A/a, B/b and C/c, considered in pairs (A and B, B and C, C and A)1. When there is uncertainty whether the tetrads of a particular organism are ordered or not, use can be made of tetratype frequencies to estimate the frequencies of partial and complete spindle overlapping at the second division of meiosis. It is important to recognize such overlapping, since it may lead to inaccurate mapping of the centromeres, and, moreover, partial spindle overlap may mimic the effects of two-strand double cross-overs across the centromere. Thus the excess of such cross-overs found by Lindegren and Lindegren2 in N. crassa has been attributed3 to spindle overlapping, although there is good genetic evidence that such overlapping is not responsible4.

Cytology of Conifers

In Cephalotaxus drupacea var. pedunculata a case of partial failure of spindle during both divisions of meiosis in pollen mother cells has been re-corded. A wide variety of distribution has been observed at M.I, A.I, and AM. The chromosomes are scattered at all phases because of the lack of a directive influence of the spindle. Since there is no correlation between these arrangements at different stages it is concluded that many of these are supurious being caused by smearing per se. The chromosome division takes place normally in absence of a spindle and 48 chromatids are seen at the end of the meiosis. There are no other abnormalities.Inspite of this abnormality there is a tendency of forming two nuclei at telophase I and four at telophase II. Tetrads are produced upto 46.7% and the rest constitute monads, diads (equal or unequal) triads and polyads containing upto 10 microspores. As expected all the cell walls are not laid by cell plate but there is evidence that wall formation takes place by furrowing.Since normal and abnormal trees grow side by side it is concluded that the cause of the abnormality is genic rather than environmental. Furthermore, it may be said that such a genic control of spindle expresses itself under certain internal environmental conditions because both normal and abnormal cells are found within the same microsporangium. In this sense it appears that the genic control is not completely dominant.

Structure and behaviour of a chromosome derivative with a deleted kinetochore.

(1) In rye, a small chromosome derivative possessing a deleted kinetochore is studied throughout meiosis and at metaphase of mitosis. Its kinetochore has, at pachytene, approximately one third the length of the normal kinetochore and is constituted by a weakly stained fibrilla pair and a chromomere pair. These two components are considered to correspond to half of the exterior and median zones of the normal kinetochore. (2) The chromosome derivative has essentially the same ability to move to the spindle poles as a chromosome with a normal kinetochore, since it is not eliminated during the mitotic divisions leading to the formation of the roots and the flowers, and since its degree of elimination is very small at both meiotic divisions. It occupies in the mitotic metaphase plate a central position similar to that of other small chromosomes with normal kinetochore. It also divides regularly at the first division of meiosis, elimination and non-disjunction seldom occurring. (3) Its behaviour differs from that of chromosomes with a normal kinetochore in that it suffers very little elimination at the second division of meiosis. Usually, rye univalents with a normal kinetochore which divide at the first division lag and are eliminated to a large extent at the second division. Moreover, its condensation cycle diverges from that of the A chromosomes. At pachytene it is about 16 times smaller than an A chromosome whereas at metaphase II it is only three times smaller. (4) At pachytene the single chromosome derivative becomes split into two clearly individualized sister chromatids earlier than the A chromosome bivalents. However, the chromatids do not separate at diplotene and the chromosome continues condensing until metaphase I where it looks like a dark round body. The two hidden chromatids only separate at middle anaphase I. Chromatid individualization does not necessarily lead to an immediate separation—the timing of the two processes being distinct. (5) The chromosome derivative was found in the third generation of a plant where another chromosome type with a normal kinetochore showed at pachytene non-homologous pairing and chiasma formation between its arms. Crossing over involving the kinetochore and one arm may account for the formation of chromosome types with an incomplete kinetochore as is the case of the chromosome derivative.

Central Body in the Male Reproductive Cells of the Silkworm with Special Reference to a Peculiarity of Centriole Division in Meiosis

1) The central body of the silkworm was traced in unbroken continuity from resting spermatogonia to spermatids, and the observations were compared with those in other animals.2) Each spermatogonium exhibits a centrosome, which consists of an idiozome and a pair of short rod-shaped centrioles at the midst of the idiozome.3) At the beginning of the growth period of the primary spermatocyte, each centriole divides into a pair of globules, so that two pairs of spherical granules are produced in each cell. At the second contraction stage, the centrioles move out of the idiozome into the area between the cell surface and the idiozome. The four centrioles elongate into elliptical or rod-shaped bodies, each extruding an axial filament from the distal tip and they are frequently in contact two by two at the proximal tips, forming two V's. The idiozome disappears in the dispersion stage.By the diakinesis stage, the centrioles divide again into four pairs of spherical granules. Thus, two pairs of spherical centrioles are distributed to each pole of the first maturation division.4) During the telophase and interkinesis, the two pairs of centrioles separate and move until they reach the positions 180° apart, so that a diplosome is found at each pole of the second maturation division which is distributed unchanged to each spermatid.5) It is most significant that the centrioles increase in number up to the diakinesis stage to become as many as in all four spermatids together, and so the total amount of centrioles remains unchanged throughout the two meiotic divisions, in marked contrast with the somatic divisions. This relation is in agreement with the majority of extensive observations carried out by many authors on various animal species.

Inheritance of Mating Type and a Lethal Factor in Cosmarium Botrytis Var. Subtumidum Wittr

Summary.-The heterothallic strains of Cosmarium botrytis var. subtumidum Wittr. provide the first material for genetic investigations in the desmids. As aresult of the survival of only two non-sister-nuclei following the second division in meiosis, two gonesrather than four are producedby a germinating zygospore.The mating type of sexual strains is shown to be determined by a single gene,whichsegregatesinthenormal Mendelianfashion. The two mating typessegregate, as a rule, in thefirst divisioni of themeioticprocess; therefore, the twogonesfroma single zygospore are usually of different mating types. The abortion of all zygotes resulting from certain backerosses of gones with theminus parental strain is due to a single factor which is undetectable in thehaploid vegetative cell or in the heterozygous condition in the zygote. Zygotes formed bythefusion of two gametes, each carrying thelethal factor, always lyse shortly aftertheir formation. The lethal factor is inherited as a single gene,