Showing papers on "Ploidy published in 1973"

The chromosomes of CHO, an aneuploid Chinese hamster cell line: G-band, C-band, and autoradiographic analyses.

Abstract: Chinese hamster ovary cells (line CHO) have been used extensively for metabolic, genetic, and radiobiological studies with only a superficial appreciation for the degree of aneuploidy characteristic of the line. A thorough karyologic analysis of CHO chromosomes using autoradiographic replication patterns, as well as centromere band (C-band) and Giemsa band (G-band) analysis, is presented. Our results demonstrate that only 8 of the 21 CHO chromosomes are normal when compared with euploid Chinese hamster chromosomes. In the 13 altered chromosomes, we found evidence of translocations, deletions, and pericentric inversions. These altered chromosomes have been characterized with respect to both origin and destination of translocated material. With the exception of the X2 chromosome, essentially all of the euploid chromatin is present in CHO cells. Autoradiographic replication patterns show that the normal sequence of chromosomal DNA synthesis is altered. Some sites which replicate late in euploid cells replicate early in CHO, and several late-replicating chromosomes in CHO cells replicate in early- or mid-S in euploid material. These studies may serve to elucidate the observed differences in mutagenic behavior between euploid fibroblasts and CHO cells.

Genetic Mapping in Saccharomyces IV. Mapping of Temperature-Sensitive Genes and Use of Disomic Strains in Localizing Genes.

Abstract: Through use of tetrad, random spore, trisomic, and mitotic analysis procedures a large number of genes, including 48 new genetic markers, were studied for their locations on the genetic maps of the yeast Saccharomyces cerevisiae. Eighteen new centromere linked genes were discovered and all but one was located on various ones of the 16 previously-established chromosomes. Five fragments of linked genes were also assigned to chromosomes; four were located on known chromosomes while the fifth determined one arm of a new chromosome. The experiments indicate that seventeen is likely to be the haploid chromosome number in this yeast. Most chromosomes have been established by genetic means to be metacentric and their genetic lengths vary from 5 cM to approximately 400 cM. Functionally-related sets of genes generally were found to be dispersed over the genome.

Potential genetic resources in tomato species: clues from observations in native habitats.

Abstract: Interspecific hybridization is playing an increasingly important role in the breeding of improved cultivars of higher plants. Lycopersicon is a good example of a genus in which the cultivated species (L. esculentum Mill.) is being improved in this fashion. The advantages offered by the tomato species for this purpose are: a. All species can be readily grown for experimental purposes, and L. esculentum is widely cultivated under a wide range of environmental conditions. b. Excellent sources of germ plasm now exist in the wild species as well as in modern and primitive cultivars of L. esculentum. c. All of the wild species can be hybridized with L. esculentumn, albeit requiring special aids in certain combinations; fertility and viability of the hybrid generations permit the intended gene transfers. All species have 12 pairs of chromosomes, which are essentially homologous. d. The cultivated species is well known genetically; its chromosomes have been mapped cytologically and genetically; it behaves as a basic diploid (27, 28).

Selective Chromosomal Elimination during Haploid Formation in Barley Following Interspecific Hybridization

Abstract: Cytological observations were made on embryo and endosperm tissues with different genome combinations that were produced by crossing the diploid and tetraploid cytotypes of Hordeum vulgare and H. bulbosum. The high frequency of barley haploids results from hybridization followed by the selective elimination of bulbosum chromosomes during the early development of embryos which initially contained a ratio of 1 vulgare to 1 bulbosum genomes. Elimination is gradual as indicated by the increase in the percentage of cells with the gametic chromosome number. However, the balance between genetic factors of the two parents appears to regulate the stability or elimination of chromosomes. Triploid embryos containing 1 vulgare to 2 bulbosum genomes are relatively stable. The most stable endosperm tissues examined had a ratio of 1 vulgare to 4 bulbosum genomes. Evidence of genetic control in both the vulgare and bulbosum chromosomes and their interaction is discussed. As has been suggested by Lange (1971) and also found in mammalian somatic cell hybrids, the most probable basis for selective chromosome elimination relates to mitotic rhythm and the duration of cell cycle phases.

Selection from Solanum tuberosum group phureja of genotypes combining high-frequency haploid induction with homozygosity for embryo-spot

Abstract: In this article the term ‘pollinators’ refers to diploid genotypes of Solanum tuberosum Group Phureja which are used to pollinate autotetraploid potatoes for the induction of autonomous growth of unfertilized egg cells. Plants obtained from such egg cells contain chromosomes of the female only and are called dihaploids. The successful selection of ideal pollinators from Group Phureja is described. A pollinator is considered to be ideal, if it has good male fertility, homozygosity for the dominant seed marker embryo-spot and the ability to induce in autotetraploid cultivars a high number of dihaploids both per berry and per 100 seeds. Embryo-spot is a deep purple or reddish coloration at the base of the cotyledons of the embryo, visible on both sides of the flat seeds. It is one manifestation of a set of complementary genes with pleiotropic action, causing a concentration of anthocyanins at the base of all plant organs that are homologous to leaves. The complementary genes are: a basic gene P for anthocyanin production (this is the seedling marker ‘coloured hypocotyl’) and allele B d of locus B. Thirty-three homozygous B d B d PP plants and 41 B d bPP plants were identified and a number from both classes tested as pollinator onto varieties. Among the homozygous group a number of ‘ideal pollinators’ could be detected. Unexpectedly a few polyploids grew from spotless seeds when using homozygous pollinators on varieties; 1.4% showed purple hypocotyl and 2.6% were matroclinous. The latter group of polyploids probably may have arisen from ‘unreduced’ egg cells of the cultivars used. In the progenies from crosses between recessive cultivars (bbbbpppp) and heterozygous pollinators (B d bPP) the ratio of spotted: spotless hybrid seeds appeared to deviate greatly from 1:1. This is ascribed to ‘unreduced’ gametes, which originate during meiosis, presumably through lack of formation of the ‘reductional’ (= first division) cell wall. On this assumption a map distance of 30 and 24 cross-over units is estimated for locus B on the basis of the proportion of nulliplex tetraploid hybrids in two different crosses. High- and low-seed-set pollinators were found at a ratio of 8:21 suggesting monogenic dominance of low seed-set. Seeds per berry and haploids per berry are significantly correlated using low-seed-set pollinators on cultivars, but they are not when pollinators are used that produce high numbers of seeds per berry. A hypothesis is put forward to explain this phenomenon.

Independent control of ribosomal gene replication in polytene chromosomes of Drosophila melanogaster.

Abstract: The saturation values for ribosomal RNA hybridization have been determined for DNA from diploid and polytene tissues of Drosophila melanogaster. These values have been measured in XO and XX larvae which have, respectively, one and two nucleolus organizers in the diploid chromosome set. The results show that (1) in diploid cells the ribosomal (r)DNA is present in amounts proportional to the number of nucleolus organizers, (2) in polytene cells the rDNA is under-replicated with respect to the euchromatic DNA, and (3) in polytene cells the amount of rDNA is independent of the diploid number of nucleolus organizers. These observations suggest that somatic variations in rDNA content may involve independent polytenization of the nucleolus organizer without change in the number of ribosomal cistrons per organizer. The independent polytenization of rDNA is proposed as the chromosomal explanation for the relative increase in rDNA in flies of the XO constitution.

Double-bridge hybrids of Solanum bulbocastanum and cultivars of Solanum tuberosum

Abstract: Solanum bulbocastanum (2n=2x=24) has valuable characters for potato breeding, but cannot be hybridized directly with S. tuberosum cultivars. Both S. acaule (2n=4x) and S. phureja (2n=2x) were used as bridging species. Triploid S. acaule × S. bulbocastanum were doubled with colchicine and the resulting fertile hexaploid F1's crossed with S. phureja. The triple hybrids obtained were tetraploid or nearly so. The two genomes of S. acaule in these triple hybrids probably pair preferentially, which may provoke pairing and possibly crossing over between the chromosomes of S. bulbocastanum and S. phureja. More than 20000 pollinations of the triple hybrids with four potato cultivars had to be made to produce 40 quadruple hybrids. These highly vigorous hybrids varied greatly in many morphological characters, resistance to Phytophthora infestans, fertility and crossability. The chromosome numbers are 48 (24 hybrids), 49 and 46, but some higher ploidy levels (65, 66, 72 chromosomes) were found as well. Their origin is to be sought in the fusion of an unreduced egg cell from triple hybrids (either euploid or hypoploid) and a reduced male gamete from the cultivars. This view is corroborated by their extreme resistance to Phytophthora. Also some 48-chromosome hybrids are highly resistant, which may indicate introgression from S. bulbocastanum. Most quadruple hybrids are readily inter-crossable and crossable as females with cultivars; several also as males. Two could be hybridized with S. bulbocastanum, but the few seeds dit not germinate. Studies of pachytene stage of meiosis revealed the presence of a S. bulbocastanum chromosome in at least one tetraploid hybrid, which is highly resistant to Phytophthora. At metaphase I of meiosis chromosome associations higher than quadrivalents were not found. Except in one hybrid, the frequency of quadrivalents did not exceed one per cell and the average proportion of chromosomes associated as bivalents amounted to 90%. The quadruple hybrids (‘double-bridge’ hybrids) appear good starting material for breeding programmes aimed at introducing genes from S. bulbocastanum into S. tuberosum cultivars.

The Origin of Diploid Neospecies in Clarkia

Abstract: Examples are given of diploid species of Clarkia that may be considered neospecies relative to other species which they closely resemble and from which they probably have been derived. It is proposed that each of these neospecies arose from a rapid and largely fortuitous reorganization of chromosomes following inbreeding in a population of extremely small size. As one test of this hypothesis, neospecies and their putative parents are compared with respect to characteristics one would expect them to have on the basis of the hypothesis No evidence was found to be inconsistent with the hypothesis.

Evolutionary conservatism in arrangement of genetic material. A comparative analysis of chromosome banding between the rhesus macaque (2n equals 42, 84 arms) and the African green monkey (2n equals 60, 120 arms).

Abstract: The diploid number of the Rhesus macaque, Macaca mulatta, is 42. All chromosomes are biarmed and all constitutive heterochromatins are centromeric. The diploid number of the African Green monkey, Cercopithecus aethiops, is 60. Again all chromosomes are biarmed, but seven pairs possess very short second arms which are heterochromatic. The heterochromatins of remaining chromosomes are centromeric. Using G-banding and deleting the heterochromatic short arms, the chromosomes of the African Green monkey can be artificially fused to reconstruct a karyotype of the Rhesus with only one pair of unmatched small metacentrics. In addition to the Robertsonian type of translocations, several sets of centromere-telomere translocations were found. The latter type of translocation reduced three arms into two. Thus the fundamental number can be changed by two mechanisms: growing extra heterochromatic arms and the centromere-telomere fusions.

Detection of Genetically Active Chemicals Using Various Yeast Systems

Abstract: Most work in yeast genetics has been performed with two species, Saccharomyces cerevisiae and Schizosaccharomyces pombe. For a detailed description of the respective life cycles, see Mortimer and Manney(1) in Volume 1 of this series. It must be pointed out that both organisms can be cultivated as haploids and, in the case of Sacch. cerevisiae, in stable diploid forms as well. Since there are a great variety of yeasts of the Saccharomyces type which do not behave in this ideal way, all genetic experiments should be performed with strains currently used by yeast geneticists. Such strains are physiologically dioecious (see Esser(2) for definition of this term), whereas many strains isolated from nature are self-compatible and haploid cells fuse uncontrollably to form diploids. Typically, Saccharomyces strains which are physiologically dioecious are available in a stable haploid or stable diploid form. The haploid cells can be mated to other haploid cells to form diploid zygotes which initiate a stable diploid phase. There is only one way to convert diploid cells into haploid cells, and this is via meiosis, which can be induced on special media. The advantage of Sacch. cerevisiae is based on the fact that each haploid cell can act as a gamete and each diploid cell can be induced to undergo meiosis, a unique situation indeed. Schizosaccharomyces can be cultured in a diploid state as well, but this diploid phase is not as stable as that of Sacch. cerevisiae; haploidization can be achieved by treatment with parafluorophenylalanine. (3, 4)

The effect of B chromosomes on homoeologous pairing in species hybrids

Abstract: The effect of B chromosomes on chromosome pairing at meiosis was investigated in the species hybrid Lolium temulentum x L. perenne at both the diploid and tetraploid level. The presence of B chromosomes drastically reduced association of homoeologous chromosomes in both the diploids and tetraploids. This was evident from the high frequency of univalents recorded in PMC's of diploid hybrids with B's and from the predominantly bivalent association of homologous chromosomes in tetraploids of this type. In the absence of B's homoeologous pairing was extensive giving a high frequency of bivalents in the diploids and multivalents as well as bivalents and univalents in the tetraploids.

The structure of mammalian chromosomes.

Abstract: Publisher Summary This chapter discusses the structure of mammalian chromosomes. The proteins, the organization of the genes into discrete chromosomes, the interaction of the chromosomes with the mitotic apparatus, the compartmentalization of the genetic system within the nuclear membrane, and the mechanism of cell differentiation all make up the eukaryotic genetic system. The chapter discusses a chromosome model that explains most major observations in molecular terms. It describes the organization of DNA into chromatin and the organization of a chromatid. The process of meiosis in chromosomes and the arrangement of genes in chromosomes are also discussed. The chapter then explains genetic exchange in meiosis and gene redundancy. Chromosome breakage and reunion chromosome shattering and fragmentation are also explained. The distribution of newly synthesized DNA to daughter chromatids is determined by heterolabeling, isolabeling, and endoreduplication distribution patterns.

Multiplicity of ribosomal RNA genes in Vicia species with different nuclear DNA contents.

Abstract: THERE is widespread variation between species of higher plants in amounts of nuclear DNA. In ten species a fifty-seven-fold variation in amounts of DNA per nucleus for equivalent cells was recorded1 and later reports showed wide ranges in the DNA contents of diploid species within single families (forty-fold in the Ranunculaceae2 and sixty to eighty-fold in the Droseraceae3). Most strikingly, large differences exist within a single genus between species with the same diploid chromosome number, for example, a three-fold range in the genus Lathyrus4 and between five and seven times as much nuclear DNA in Vicia faba as in V. sativa5–7. The structural basis of these variations is unclear although models of either a single stranded chromosome, in which DNA content increases by longitudinal multiplication of DNA sequences, or a multi-stranded chromosome, where increase is by lateral increase of strands, have been suggested (see reviews, refs 8, 9).

Chromosomal polymorphism caused by supernumerary chromosomes in the field mouse, Apodemus giliacus.

Abstract: Chromosome studies were made on 74 animals of the field mouse, Apodemus giliacus, a new form of the genus Apodemus described by Kobayashi and Hayata (1970). Extreme variations in number and morphology of chromosomes was observed. While the diploid numbers varied from 48 to 61, the number of acrocentric elements was consistently 48, except for one specimen which had 40 such elements. In contrast, the number and constitution of several biarmed elements and microchromosomes were highly variable in the complement, and, hence, responsible for the polymorphism. Karyotype analysis of meiotic chromosomes, on the basis of Giemsaand quinacrine-stained preparations, some familial studies and breeding experiments revealed that variable elements were supernumeraries of a hitherto undescribed type, whereas the 48 acrocentrics seemed to represent regular autosomes and sex elements. Most of the supernumeraries did not show pairing at metaphase I, but some did form bivalents. Usually, the supernumerary biarmed chromosomes were of regular size and fluoresced rather brightly over their entire length, suggesting that they were heterochromatic in nature. Considering the above findings and other relevant data of some allied species, the differentiation between A. giliacus and A. speciosus might have occurred rather recently, when the former species might have been involved in rapid and divergent chromosomal evolution.

Karyotypes of squirrel monkeys (Saimiri sciureus) from different geographic regions

Abstract: Three different karyotypes have been found so far among Saimiri originating from five different South American localities. All animals examined have the same diploid number (44) of chromosomes but the number of acrocentric and submetacentric chromosomes varies, presumably as a result of pericentric inversions. Saimiri originating from Iquitos, Peru, consistently have ten acrocentric chromosomes; animals originating from Leticia, Colombia, have 12 acrocentric chromosomes. Hybrids produced in our laboratory have the expected 11 acrocentrics and one unpaired submetacentric chromosome. Animals originating from Guyana have fourteen acrocentric chromosomes and the expected two fewer submetacentric chromosomes. Squirrel monkeys from Costa Rica, Panama, and Pucallpa, Peru, studied to this date conform to the Iquitos type with ten acrocentric chromosomes. These findings point to genetic differences which may result in variable responses to laboratory situations. The evolutionary factors involved in this rearrangement of chromosomes and possible influences on phenotypes are subjects of interest for future study. The importance of identifying the source of squirrel monkeys used in biomedical research is apparent if results from different laboratories are to be repeated or compared.

Mitochondrial genetic analysis by zygote cell lineages in Saccharomyces cerevisiae.

Abstract: Yeast strains were constructed carrying multiple mitochondrial markers conferring resistance to the inhibitors erythromycin, chloramphenicol, paromomycin and oligomycin. A pedigree analysis of two crosses was made by micromanipulating buds from zygotes. The first few daughter buds isolated from the zygotes sometimes gave rise to diploid clones which had a mixture of mitochondrial types. All possible classes of mitochondrial parental and recombinant types were found although they never appeared all together as the progeny from a single zygote. It was inferred that multiple recombination events took place in zygotes and in some of the buds derived from them. After removal of the first four or so daughter buds, subsequent buds from the zygote carried one mitochondrial type only. In cross I in which three markers were analyzed this was most frequently one of the parental types. In cross II (involving four mitochondrial markers) the later buds from the zygotes were frequently of recombinant mitochondrial type.

Studies of multipolar mitoses in euploid tissue cultures. I. Somatic reduction to exactly haploid and triploid chromosome sets.

Abstract: Cultures of kidney epithelium and fibroblasts of 39 specimens of Microtus agrestis were investigated. In all 77 cultures multipolar mitoses were found. They were studied in living state and after pulse labelling with 3H-thymidine. The ploidy of the multipolar mitoses and of their daughter nuclei was determined by measuring the relative Feulgen-DNA content and by counting the predominantly constitutive heterochromatic sex chromosomes. Constitutive heterochromatin was demonstrated by late replication, retarded separation of the chromatids in anaphase, heteropycnosis and by the Giemsa technique of Arrighi and Hsu (1971). The latter stained also the spindle apparatus of mitoses.—In living cells, transformation of multipolar mitoses into bipolar mitoses was observed. The chromosomes of multipolar mitoses are separated into complete genomes; the daughter nuclei can be haploid, diploid, triploid or tetraploid. The chromosomes of haploid and triploid metaphases were studied with the Giemsa banding technique. The banding pattern shows an exact monosomy and trisomy, respectively, for each chromosome. Haploid nuclei are likely to be viable only in multinucleate cells, whereas triploid cells behave like diploid cells during the S period and the mitosis.

Chromosome and chromatid exchanges in chinese hamster cells

Abstract: Chromosomes were studied by autoradiography in a mixed culture of diploid and tetraploid cells, after having induced fusion with Sendai virus between two Chinese hamster cell populations, one labelled with 3H-, the other with 14C-thymidine; sister chromatid exchanges were studied in the 3H diploid cells and exchanges between chromosomes in the 3H-14C tetraploid synkaryons. In both cases, the frequency of exchanges increases after U. V. irradiation.

Parthenogenetic development of mouse embryos in vivo. II. Postimplantation development.

Abstract: Newly ovulated eggs from CBA-p and CBA-T6T6 inbred strains were activated in situ with an electric shock of 20–50 V. Both spontaneously ovulating females mated with vasectomized males (strain A) and those induced to ovulate and kept apart from males were used. The immediate reaction of eggs was examined 5–7 h after activation and their subsequent development was followed every day up to the 6th day (eggs examined on the 5th and 6th day were tube-locked by a ligature). In spontaneous ovulators the highest yield of activated eggs was obtained following 30 V shock (75%), with a mean for four series (20, 30, 40 and 50 V) of 46·1%. The most common reaction is extrusion of the second polar body (2 PB) and formation of one pronucleus (about 70% of activated eggs). Other types of reaction include: immediate cleavage, suppression of 2 PB with formation of two or, very rarely, one pronucleus. Thus the majority of eggs are potentially haploid. No relationship between the frequency of various types of reaction and the strength of the shock (voltage) was observed. Up to the 3rd day cleavage proceeds at a normal rate and appears to slow down during the 4th day. In spontaneously ovulating females the incidence of blastocysts among developing eggs rises from 3·4% on the 4th day to 52·5% on the 5th day; the corresponding figures for induced ovulations are 10% and 23·6%. Some embryos despite being composed of a large number of cells (40–120) do not undergo cavitation and remain morulae. On the basis of karyological examination of 60 embryos with analysable metaphase plates 60% were classified as haploid, 16·7% as diploid, 1·7% as tetraploid and 21·6% as haploid/diploid mosaics. During early cleavage binucleate blastomeres (a presumed step in regulation from n to 2 n ) were observed only in eggs from induced ovulations. In embryos developed from spontaneously ovulated eggs n /2 n mosaics were observed for the first time on the 5th day. In general, spontaneously ovulated eggs developed better after activation (both in quantitative and qualitative terms) than those obtained following hormonal treatment.

Dosage Compensation in DROSOPHILA MELANOGASTER Triploids. II. Glucose-6-Phosphate Dehydrogenase Activity.

Abstract: The level of activity of the enzyme glucose-6-phosphate dehydrogenase was determinel in flies having seven different chromosomic constitutions. All those having an integral number of chromosomes [XAA, XXAA, XAAA, XXAAA, and XXXAAA (X=X chromosome, A=set of autosomes)] were found to have similar units of enzyme activity/mg live weight, while diploid females with a duplication and triploid females with a deficiency showed dosage effect. The amount of enzyme activity per cell, on the other hand, is also independent of the number of X's present but appears roughly proportional to the number of sets of autosomes.—It is proposed that dosage-compensated sex-linked genes are controlled by a positively acting regulatory factor(s) of autosomal origin. With this hypothesis it is possible to explain dosage compensation as a consequence of general regulatory mechanisms without invoking a special device which applies only to the X chromosomes.

The duration of meiosis in a diploid rye, a tetraploid wheat and the hexaploid triticale derived from them

Abstract: Meiosis and pollen development were timed in diploid rye, Secale cereale L. cv. Prolific; tetraploid wheat, Triticum turgidum L. var. durum cv. Stewart; and a hexaploid, Triticale hexaploide cv. 6A190, derived from them. At 20 C the duration of meiosis was about 51 hr in Prolific rye, 31 hr in Stewart wheat, and 37 hr in 6A190 triticale. Pollen development at 20 C lasted about 16 days in Prolific rye, about 9.5 days in Stewart wheat, and about 10 days in 6A190 triticale. These times are in close agreement with estimates previously made for diploid rye, cv. Petkus Spring; tetraploid Triticum dicoccum; and hexaploid triticale cv. RosnerThe high nuclear DNA content of rye pollen mother cells (PMC's) determines a longer meiotic time in both diploid and tetraploid rye than that determined by the lower nuclear DNA contents of PMC's in diploid and tetraploid wheat. The data available may be interpreted to indicate that the relative effect of the wheat and rye genomes in determining the rate of meiotic developmen...

Haploidy in Brassica nigra Koch

Abstract: Meiotic behaviour of haploid plants of Brassica nigra which arose parthenogenetically amongst the progeny of B. nigra × B. campestris, is described. The presence of two bivalents and s-s associations suggests the basic chromosome number w as six and the present x=8 number arose through the duplication of two of the original chromosomes.

Chromosomal localization of human haemoglobin structural genes: techniques queried.

Abstract: Price, Conover and Hirschhorn1 have reported the in situ hybridization of haemoglobin mRNA to diploid chromosomes. We think such a conclusion to be impossible because the specific activity of their mRNA was 6 × 10−7 disintegrations per mRNA molecule during the two week exposure of their autoradiographs. As a genome has been reported to contain less than five haemoglobin cistrons2, even if hybridization and autoradiographic efficiencies were 100%, then at most only 6 × 10−6 silver grains would have been produced over the diploid cell's haemoglobin loci.

Cytogenetics of ticks (Acari: Ixodoidea)

Abstract: Haemaphysalis longicornis consists of diploid bisexual races (20+ XX♀; 20+X♂), triploid obligatory parthenogenetic races (30–35 chromosomes) and an aneuploid race capable of bisexual and parthenogenetic reproduction (22–28 chromosomes). Karyotypes were analyzed for each race. Hybridization failed between diploid and triploid races, but succeeded between bisexual diploid males and parthenogenetic aneuploid females. F1 and F2 progeny were produced and their chromosomes studied. Crossing of F1 progeny to a bisexual race was successful. Parthenogenetic ability was almost completely lost in F1 and F2 females. Several possible modes of evolution from diploid bisexual individuals to triploid parthenogenetic ones are discussed as is species characterization in taxa with races reproducing bisexually, parthenogenetically and by a combination of both methods.

Repeated and non-repeated nucleotide sequences in diploid and polyploid wheat species

Abstract: Reassociation rate studies of dissociated DNAs from diploid, tetraploid and hexaploid wheat species revealed that all the species have a large proportion of their DNA which shows characteristics of repeated DNA, under the conditions used in the reassociation experiments (fragment size about 450 nucleotide pairs, incubation at 60° C. in 0·12 M phosphate buffer, C0t = 100). The relative proportion of this fraction increased with ploidy in tetraploid and hexaploid wheat. Genome size (amount of non-repeated DNA) was larger in hexaploid and tetraploid wheat in comparison with diploid wheat. Heterologous reassociation of repeated and non-repeated fractions of DNAs showed considerably more divergence in the repeated sequences at both diploid and at polyploid levels. Non-repeated sequences of wheat species showed greater homologies, and appear to be more conservative in composition.

Chromosome homology in the climbing rats, genus Tylomys (Rodentia: Cricetidae).

Abstract: The climbing rats (Tylomys spp.) have diploid numbers of 52 (T. panamensis), 42 (T. nudicaudus), 40 (T. n. gymnurus) and 36 (T. n. villai). Using G-band analysis we found that the variations are mainly of the Bobertsonian type, and practically all changes can be traced. G-banding also revealed that biarmed chromosomes with similar morphology may be composed of different components. Such conclusions were verified also by analysis of the chromosomes of interspecific hybrids. C-band staining showed that the constitutive heterochromatin of Tylomys is mainly located in the centromeric regions and the sex chromosomes, a situation similar to that of Microtus agrestis. In one specimen of T. panamensis, however, an additional terminal heterochromatic segment was found in one member of the large metacentric pair. Our data underline that in mammalian cytotaxonomy studies both C- and G-band (or C- and Q-band) techniques must be applied to gain maximal information.

The location of a recessive gene for chlorophyll deficiency in diploid Solanum tuberosum by means of trisomic analysis.

Abstract: A light green monogenic recessive mutant was found in diploid Solanum tuberosum. The mutant gene (v) was located by aneuploid analysis on the extra chromosome of a trisomic (2n = 25) derived parthenogenetically from cv. Intenso (2n = 48). The extra chromosome was identified at pachytene stage as chromosome XI1 according to the numbering system of Yeh and Peloquin (1965). The mutant gene appeared to be genetically independent of the linkage group B-I-F-Ow for anthocyanin distribution and of the gene P for anthocyanin production.

Repetitive DNA in Drosophila

Abstract: Among the higher eukaryotes, Drosophila Melanogaster has one of the smallest reported genome sizes. According to the spectrophotometric data of Rasch et al. (1971) the haploid DNA content is 1.8 × 10−13g, corresponding to 1.1 X 1011 daltons or approximately 40 times the genome size of E. Coli. For this reason alone, analysis of the organization of DNA in Drosophila should be easier than in organisms with larger amounts of DNA in the haploid chromosome set. Furthermore, D. Melanogaster has only four chromosome pairs, its formal genetics is better known than that of any other eukaryote, and cytological analysis is facilitated by the existence of the giant polytene chromosomes in larval salivary glands.

Polyembryony in Soybeans1

Abstract: Twin seedlings were observed in the progeny of malesterile (msms) plants of (L.) Merrill from natural crossing blocks. Of the seedlings observed, more than 4% were embryonic twins. Triplets and conjoined individuals were also found. Cytological examinations of root-tip preparations revealed that most individual plants from twin sets were diploid (2n=40). However, diploid: haploid and diploid:triploid twin pairs were also identified. Genetic analysis of a marker trait in the twin seedlings and their selfed progeny indicated that diploid diploid sets originated primarily after cross-fertilization. Evidence suggests that the mechanism underlying the development of these twins involves a cleavage of the zygote or the development and fertilization of multiple embryo sacs within an ovule.