Chromosome Number Distribution Research Articles

Stabilization of new types of diploids (2n=22, 24) through selfing of aneuploids (2n=21, 22) derived from crossing of sesquidiploids (2n=29, AAC) and Brassica campestris (2n=20 AA)

Aneuploids with 2n=21 and 2n=22 derived from crossing of sesquidiploids (2n=29, AAC) and Brassica campestris (2n=20, AA) were selfed successively in order to follow the changes in chromosome number of the progenies for three consecutive generations. Progenies with 2n=22, 23 and 24 obtained after selfing of S0 generation and the succeeding S1, S2 and S3 generations were analyzed in terms of pollen stainability, % seed set as well as cytogenetically based on meiotic behaviour with the aim of determining the possibility of addition of one or more alien chromosomes into n=10 species which may lead to differentiation of single or plural disomic addition lines. The generation of aneuploids with 2n=21 progressed in such a way that most plants seem to revert to the 2n=20 chromosome number of B. campestris after selfing. From 2n=22 aneuploids, however, the succeeding progenies showed high frequency of plants with two additional chromosomes which accounted for 50.6% and 52.9% of total S3 progenies via 2n=22 and 2n=24 S2 generations, respectively. The meiotic behaviour of these progenies indicated evidence for a rule governing the frequency distribution of chromosome number among these addition lines and high possibility to breed such disomic plants with 2n=22. A method of selecting stable aneuploids was suggested in addition to the possible role of pollination biology at various processes of such breeding program.

Germ line-restricted supernumerary (B) chromosomes in Eptatretus okinoseanus.

Cytogenetic studies were performed on two types of Japanese hagfish (Eptatretus okinoseanus) that eliminate about 45% (type A) and 55% (type B) of their DNA from presumptive somatic cells during the differentiation of somatic cells. The observations revealed inter- and intraindividual variations in the number of chromosomes in germ cells of both types of hagfishes. Although the modal number of chromosomes in the germ cells was 54 in both types, the percentage of cells with the modal number was rather low (38.6% [51/132] in five specimens of type A and 22.7% [25/110] in eight specimens of type B). In addition, one of seven type B specimens clearly had a modal number of 62 chromosomes. Another specimen of type B had a bimodal distribution of chromosome numbers, with peaks of 54 and 59 chromosomes. The observation of interindividual variations was supported by data on the amount of DNA in germ cells of type B specimens. However, these variations were rarely observed in somatic cells. These results suggest that supernumerary (B) chromosomes are maintained in germ cells and are eliminated together with some other chromosomes and/or chromatin from somatic cells.

Karyotypic change from heteroploidy to near diploidy associated with development of cisplatin resistance in a rat ovarian tumour cell line

In a rat ovarian tumour cell line a 33-fold resistance to cisplatin (O-342/DDP) was developed in vitro by continuous exposure of the parental cell line (O-342) to stepwise increase cisplatin concentration in the culture medium. Both cell lines had a similar growth rate in vitro. Development of resistance was accompanied by a change of the karyotype from heteroploidy in chemosensitive O-342 cells to near diploidy in resistant O-342/DDP cells as shown by chromosome number distribution. This finding was confirmed by measuring cellular DNA content using flow-cytometry analysis. Flow karyotyping showed significant differences in chromosomal DNA contents between both cell lines. Our results suggest that the parent line O-342 consists of at least two subpopulations, a cisplatin-sensitive and a cisplatin-resistant one, corresponding to hyperploidy and near diploidy, respectively. Continuous cisplatin exposure of O-342 cells selectively killed the sensitive fraction, resulting in the karyotypic change observed.

Chromosome number distribution and cellular DNA content in colorectal adenomas from polyposis and nonpolyposis patients

Ploidy analyses of colorectal adenomas were performed by combined flow cytometric DNA analysis of unfixed isolated nuclei and direct chromosome preparation after Colcemid incubation for 9–20 hours. Ten of 18 adenomas from nonpolyposis patients and 4 of 13 adenomas from patients with familial adenomatous polyposis yielded a mean of 25 countable metaphases (range 7–44) per tumor. Of 343 metaphases, only 38% had 46 chromosomes, and 62% were nondiploid. All but one adenoma had diploid or peridiploid modes in the range of 46–50 chromosomes. One adenoma was hyperploid, with a mode of 74 chromosomes and a correspondingly increased nuclear DNA content. In another two adenomas, the DNA analyses showed small hyperploid populations constituting 6% and 2% of the cells. The most striking difference between the DNA analyses and chromosome number distributions was that 13% of all metaphases were hyperploid with chromosome numbers outside the perimodal range but, except in one adenoma, without indication in the DNA histogram of corresponding hyperploid cell populations. We propose that these aberrant metaphases indicate an early acquired genetic instability of the neoplastic epithelium, which may be instrumental in generation of hyperploid, invasive clones, which constitute most colorectal carcinomas.

Discrepancies among the metaphase, telophase, and the G0/G1 and G2 DNA peaks of heteroploid cell lines

Heteroploid cell populations often show narrow peaks of G0/G1 and G2/M DNA content and broadly distributed chromosome numbers. This was originally explained by the selective metaphase arrest of the cells that have non-modal chromosome numbers. To test whether this explanation applies, we have measured the chromosome number distributions, as well as the G0/G1, G2, metaphase (M), and telophase (T) DNA distributions, of the cell lines WCHE-5, MCa-11, and HL-60. The WCHE-5 cells had narrowly distributed chromosome numbers and G0/G1 G2, M, and T DNA peaks. The MCa-11 and HL-60 cells also had narrowly distributed G0/G1 and G2 DNA peaks, but broadly distributed chromosome numbers and M and T DNA peaks. The widths of the MCa-11 and HL-60 M- and T-cell DNA peaks were similar to those of their chromosome number peaks, suggesting that all cells were completing mitosis, regardless of chromosome number or DNA content. Thus, selective metaphase arrest does not seem to be the cause of the narrow G0/G1 and G2 DNA peaks of heteroploid cell populations.

Allozyme Variation in Coreopsis Sect. Coreopsis (Compositae)

An electrophoretic study of the nine species of Coreopsis sect. Coreopsis (C. auriculata, C. basalis, C. grandiflora, C. intermedia, C. lanceolata, C. nuecensis, C. nuecensoides, C. pubescens, and C. wrightii) revealed high genetic identities (above 0.90 for most comparisons) for all species. Uniformly high identities among all taxa made it difficult to discern patterns of relationships among the species in sect. Coreopsis. Similar levels of gene diversity were found in perennial and annual species in the section, and between geographically widespread vs. more restricted species. It is suggested that the high identities result from the recent divergence among the species in sect. Coreopsis, which is viewed as a highly evolved section within North American Coreopsis. The genus Coreopsis in North America consists of 11 sections containing a total of about 44 species. The genus is distributed throughout Mexico, California, and the eastern and southeastern United States. The sections are welldefined with regard to chromosome number, morphology, and geographic distribution (Smith 1975). Attempts to produce artificial hybrids between plants of different sections have, for the most part, failed, while there is some intercompatibility and interfertility between species within sections (Smith 1975, 1976). Section Coreopsis is the largest of the North American sections. Smith (1975) viewed it as one of the most advanced groups of North American Coreopsis. The section is native to and centered within the eastern and southeastern United States, with certain species widely distributed throughout this range while others are restricted in distribution. It consists of nine species, four of which are annuals and five are perennials. Perennial species include C. pubescens Elliott, C. auriculata L., C. intermedia Sherff, C. lanceolata L., and C. grandiflora Hogg ex Sweet. The annual species are C. basalis (Dietr.) Blake, C. wrightii (A. Gray) H. M. Parker, C. nuecensoides E. B. Smith, and C. nuecensis A. Heller. The base chromosome number for the section is n = 13. Two species, C. nuecensis and C. nuecensoides, exhibit aneuploidy (n = 6, 7, 8 and n = 9, 10, 11, respectively), and one taxon, C. grandiflora var. longipes (Hook.) Torrey & A. Gray, is hexaploid (n = 39). All species are self-incompatible and presumably strongly outcrossing (Smith 1975, 1976). Discerning evolutionary relationships within the section has proven problematical. Although the section itself is a well-defined, monophyletic group, relationships among the perennial species and origin of the annual species within the section remain unclear. However, available evidence suggests that the four annual species consist of two progenitorderivative species pairs, C. basalis-C. wrightii and C. nuecensoides-C. nuecensis, the former species in each pair representing the progenitor species (Crawford and Smith 1982a, 1982b; Smith 1974; Smith and Crawford 1981). Smith (1982) constructed a phylogenetic hypothesis for the section based largely on morphology (fig. la). He suggested that C. pubescens may represent the basal taxon within the section, and that the two progenitor-derivative annual species pairs are relatively advanced, but their origin from the perennials is obscure. His phylogeny also indicates a close relationship between C. lanceolata and C. auriculata (fig. la). The cladistic analysis of North American Coreopsis by Jansen et al. (1987) agrees in many respects with Smith's proposed phylogeny, including the separation of annuals and perennials into two distinct lines (fig. lb). Annuals are composed of two pairs, namely C. basalis-C. wrightii and C. nuecensoidesC. nuecensis, in their treatment as well. However, the cladistic study differs in that C. auriculata shows closer affinities with C. pubescens rather than with C. lanceolata as suggested by Smith (1982). Preliminary chloroplast DNA data (Crawford et al. 1988; unpubl. data) suggest that C. pubescens and C. auriculata are closely allied, and that one of these taxa (or a common ancestor) could

Mevalonate deprivation leads to aneuploidy in Chinese hamster ovary cells.

After exposure to compactin, the competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, 22% of CHO-K1 cells contained abnormally high numbers of chromosomes. In two populations of cells selected for compactin resistance 31 and 33% of the cells contain more than 22 chromosomes. Some cell lines isolated from these populations have the wild type chromosome number of 20-21, while others have a broad distribution of chromosome number, often with a mean around 36-40. Finally, Chinese hamster ovary cells that are mutant for 3-hydroxy-3-methylglutaryl-CoA reductase and therefore auxotrophic for mevalonate were starved for that compound. This treatment also increased the number of cells containing extra chromosomes. These results indicate that interruption of the cellular supply of mevalonate results in abnormal chromosome number.

Notes on pondweeds — outlines for a monographical treatment of the genus Potamogeton L.

SummaryA review of the systematics of the genus Potamogeton L. on a world wide scale is presented. There exist several problems, the causes of which are analyzed, and for which solutions are outlined as far as possible.The variability of many Potamogeton species is often underestimated leading still to superfluous descriptions of new species and hybrids. Based on own experience and reliable literature records the species are classified into three groups according to their degree of variability.The value of stem anatomical and fruit morphological characters both having received special recognition in the history of Potamogeton systematics is investigated. Both groups of characters, if handled carefully. can give a valuable contribution to the distinction of species.The hybrid problem is discussed extensively. The frequency of hybrids shows strong regional differences, which led to different judgement in the past. Those hybrids that can be regarded as sufficiently described are presented in a list. Only few of them really occur frequently.The importance of the analysis of life history and growth form in Potamogeton systematics is stressed. There exists a strong deficit in knowledge, particularly as to quantitative data. Necessary requirement for progress in study of this subject is a more precise definition of morphological terms in Potamogeton.The analysis of the geographical distribution of the species is still preliminary, as identity or non‐identity of various species of different parts of the world is un‐proven. Nevertheless, species can be classified in appr. 17 distribution types. The highest density of species occurs in Eastern North America.Evolutionary questions are discussed using certain species groups as models. The broad‐leaved, reticulateveined species are considered as most primitive, which is supported by morphological, physiological and biogeographical evidence. Appr. 15 species groups can be distinguished the actual relation of which, however, is not yet clear. Also the distribution of chromosome numbers gives no direct information, as polyploidy and aneuploidy are more frequent than so far assumed.The biosystematical problems described have caused a great taxonomical confusion. A literature research revealed more than 1300 names (incl. hybrid combinations), which most probably refer to only 80 to 90 actually existing species (plus appr. 40 confirmed hybrids). The recognized species are presented in a list ordered according to their supposed affinity. Herbarium studies showed that several not yet described species may be added in the future. Some controversial cases like P. pusillus, P. tepperi, P. fluitans, and P. pedersenii are used to illustrate typical taxonomical problems.

Comparison of Anther Culture and the Hordeum bulbosum Method for the Production of Doubled Haploids in Winter Barley

AbstractThe comparison, between the efficiency of anther culture and the Hordeum bulbosum method in barley was extended to the chromosome number distributions of all planes derived from the two techniques and the proportions of fertile doubled haploid plants which survived until maturity.The frequencies of haploid and spontaneously doubled haploid plants which were useful for practical breeding purposes were found to be around 90 % for both techniques. The remainder consisted of polyploid, mixoploid and aneuploid variants in the case of microspore‐derived plants and diploid interspecific hybrids in the progeny of the H. bulbosum method. The ploidy level distributions of the microspore‐ and H. bulbosum‐derived plants appeared to be independent of the genotype of the donor.There were no significant differences between techniques regarding the proportions, of plants which survived a severe winter and the production of fertile doubled haploid plants. Both techniques can therefore complement each other in a breeding programme and their relative merits are discussed.Possible ways of improving doubled haploid production in barley are suggested for increasing its use in breeding schemes.

Differential transmission of extra genome chromosomes in pentaploid blueberry

Transmission of extra genome chromosomes by three Vaccinium ashei (2n=6x=72)/V. corymbosum (2n=4x=48) pentaploid hybrids backcrossed to the hexaploid species V. ashei was examined. Chromosome numbers were determined for 36 and 31 progeny representing 5x × 6x and 6x × 5x type crosses, respectively. Chromosome numbers ranged from hypopentaploid (2n=4x+11=59) to hexaploid with means of 2n=66.2 for 5x × 6x progeny and 2n=68.0 for 6x × 5x progeny, representing overall extra genome chromosome gains of 3.3% and 33.3%, respectively. Extra chromosome number distributions for both the 5x × 6x and x × 5x progeny deviated significantly from the theoretical distribution assuming random chromosome transmission and were also found to be heterogeneous. The 2n=5x+9=69 class predominated in 6x × 5x progeny, while a predominate class was lacking in the 5x × 6x progeny. Higher than expected frequencies of plants with chromosome numbers near the pentaploid and hexaploid levels were found in the 5x × 6x progeny, whereas the frequency was only greater at the hexaploid number in 6x × 5x progeny. Present and previous results (Vorsa et al. 1986) indicate that extra genome chromosome transmission in oddploids can be influenced by selection at both gametophytic (pollen) and post-zygotic stages. However, post-zygotic selection may involve two different mechanisms acting concurrently: 1) chromosome imbalance due to aneuploidy and/or 2) endosperm imbalance referring to maternal: paternal genome ratios deviating from 2∶1. Such a mechanism could result in differential transmission rates of extra genome chromosomes in oddploids when crosses are made to differing ploidy levels, and to reciprocal differences as well.

Taxonomic Notes and Chromosome Numbers in Antennaria Gaertner (Asteraceae: Inuleae) from Arctic North America

Chromosome numbers of 156 individuals representing 19 species from western arctic North America are reported. Previously unreported species include A. alborosea (2n = 56, 70), A. crymophila (2n = 28, 56, 70), A. densifolia (2n = 28), A. ekmaniana (2n = 56, 70), A. elegans (2n = 28, 56, 70), A. isolepis (2n = 56), A. laingii (2n = 56), A. neoalaskana (2n = 28), A. oxyphylla (2n = 56), A. pallida (2n = 56, 70), A. philonipha (2n = 28), and A. subviscosa (2n = 28, 56, 60, 70). Two species were represented by cytotypes previously unreported, A. angustata (2n = 70) and A. monocephala (2n = 42). The remaining counts support previously reported chromosome number determinations for the respective species and are presented to supplement our knowledge relative to chromosome number distributions for these. In populations where staminate and pistillate plants co-occurred, the sex ratios were generally 1:1, but deviations from this ratio existed among the diploid species.

Cytotaxonomical studies of South Indian Capparidaceae.

Cytotaxonomical studies have been made in 18 species coming under 6 genera of South Indian Capparidaceae, of which first record of chromosome number has been made in Cleome tenella, C. felina, C. aspera, Cadaba triphylla, Capparis brevispina, C. diversifolia, C. rotundifolia and C. divaricata.The basic chromosome number ranges from n=9 to n=80. The graph drawn on the frequency distribution of basic chromosome numbers shows a polymodel curve indicating thereby the evolution of species in many directions.The basic chromosome number may be n=7, from which species with n=9, n=10, n=11 and n=13 might have arisen by aneuploidy. The basic numbers n=16, n=17 and n=18 are secondarily balanced tetraploids by means of euploidy and aneuploidy. The basic numbers n=20, n=21 and n=22 may be secondarily balanced higher polyploids. The basic numbers n=49 and n=80 may be secondarily balanced allopolyploids which might have been evolved by hybridization of any two species followed by polyploidization. Therefore, autopolyploidy as well as allopolyploidy might have played important role in the the origin and evolution of the species of South Indian Capparidaceae.

Characterization of a Human Chorionic Gonadotropin-Producing Testicular Choriocarcinoma Cell Line

A testicular choriocarcinoma cell line designated JHTK-1 was established in vitro from a mixed germ cell tumor xenografted into nude mice, and may prove to be the first human choriocarcinoma cell line of testicular origin in long-term culture. The cells have been kept in culture for three years and produce human chorionic gonadotropin persistently. The chromosome number distribution ranged from tetraploidy to septaploidy, and trypsin G-band karyotyping showed that all the chromosomes were of human origin. Dibutyryl cyclic adenosine monophosphate at a concentration of 1mM caused more than 15-fold stimulation of human chorionic gonadotropin secretion with morphological alteration in JHTK-1 cells. This suggests that dibutyryl cyclic adenosine monophosphate induces the differentiation of cytotrophoblastic cells into syncytiotrophoblastic cells among JHTK-1 cells. When JHTK-1 cells were heterotransplanted into the subcutis of BALB/c nude mice, large cystic tumors were produced with histological characteristics similar to choriocarcinoma.

Chromosomal aneuploidy in sarcoid granuloma cells.

Chromosomal examination and measurement of DNA content were performed in cultured sarcoid granuloma cells obtained from lymph node specimens of 11 patients with sarcoidosis. Chromosomal studies revealed that most of the cells were aneuploid; the chromosome number ranged from the near-haploid number to the near-diploid number, and the distribution of chromosome number was fairly wide. The DNA content of individual cells was measured by Feulgen microfluorospectrophotometry. The distribution of DNA content of the granuloma cells was fairly wide and did not show any recognizable peak. Flow cytofluorometry of DNA content of the cells also revealed wide frequency distribution of the DNA content in sarcoid granuloma cells. The majority of the sarcoid granuloma cells were aneuploid or hypodiploid in the short-term primary culture, suggesting that hypodiploidy may exist in granuloma cells of patients with sarcoidosis.

In vitro culture ofBellevalia romana (L.) Rchb.

Bellevalia romana (L.) Rchb., a monocotyledonous plant characterized by few (2 n=2 x=8) and very large chromosomes, is a useful subject for studying developmental problemsin vitro. Cytological analysis of callus revealed that the majority of cells were diploid, but the remaining cells had aneuploid nuclei with a wide range of chromosome numbers, tetraploid and haploid nuclei. The frequency of aneuploid and polyploid cells was higher in callus grown in the presence of 2,4-D than in callus grown in NAA plus BAP. These nuclei seemed to increase with the duration of culture. The chromosome number distribution as determined by chromosome counts in calli at different culture times was confirmed by DNA cytophotometry. Chromosome number mosaicism (mixoploidy and aneusomaty) also occurred in all root apices of 9 out of 46 plantlets regenerated from callusvia adventitious shoots.

Breeding, genetics and cytogenetics of the soft-furred rat, Millardia meltada. IV. Karyotype analyses of 18 mammary tumors developed spontaneously in the inguinal regions of the male specimens.

The distribution of the chromosome number and the karyotype in 18 spontaneous mammary tumors developed at the inguinal regions of the male soft-furred rat (Millardia meltada) are analysed. Among them 17 tumors show a modal occurrence of 50 chromosomes which are the normal chromosome number of this species. The karyotype of the tumor cells is not different from the normal somatic cells. One specimen has 51 chromosomes among which one trisomy (no. 16) is included. The normal karyotype of the tumor cells does not change during 10 passages in vitro cultivation. Based on the karyotype analysis the mammary tumor of the soft-furred rat is suggested to be a benign type depending on the male hormone. Table I. Chromosome number distribution of the 18 mammary tumors developed in the males of the soft-furred rat

Multiple phenotypic divergence of mammary adenocarcinoma cell clones. I. In vitro and in vivo properties.

The properties of cell clones derived from locally growing and spontaneous metastases of 13762NF mammary adenocarcinoma change during in vitro growth. This has been termed phenotypic drift and is reproducible in independent experiments using different cryoprotected cell stocks. To determine whether phenotypic drift in 13762NF cell clones is the result of an en bloc shift in the properties of all tumor cells, or independent phenotypic divergence of tumor cells to produce a mixed cell population, local tumor-derived clone MTF7 was subcloned at low and high culture passage numbers in vitro. Each subclone was analyzed in vitro for cell morphology, growth rate, saturation density, karyotype and ploidy, and in vivo for experimental metastatic behavior. Subclones derived from low passage clone MTF7 (T11; tissue culture passage number 11) were relatively homogeneous in their growth rates (doubling times of 16.8-17.4 h) and saturation densities (approximately 2 X 10(5) cells/cm2); yet, these same subclones were heterogeneous in their in vitro cell morphologies, experimental metastatic potentials (means range from 0 to greater than 100 tumor nodules per lung), size distributions of lung tumor nodules, marker chromosomes and modal chromosome numbers. High passage MTF7 (T35; tissue culture passage number 35) subclones had similar growth rates and saturation densities, except for subclone 2, which had a doubling time of approximately 26 h. Cell morphologies, experimental metastatic potentials (means range from 3 to greater than 600 tumor nodules per lung), size distribution of lung tumor nodules, marker chromosomes and modal chromosome numbers varied between MTF7 (T35) subclones. The results suggest that simultaneous, independent divergence of several phenotypes from a single cloned cell occurred to form a mixed cell population containing cells with independently segregated, unrelated phenotypes. Thus, the reproducibility of phenotypic drift in clonal cell populations was probably the result of tumor cell divergence and was not an en bloc shift in phenotypic properties of all cells.

Chromosomal alteration and the development of tumors. XXVI. A mammary cancer of the domestic cat characterized by hypodiploid and hypotetraploid modes, with a special note on increase of diploid cells after deep freezing.

Karyotypes of a mammary cancer spontaneously developed in the domestic cat were analysed in comparison with those of normal somatic cells (2n=38). This tumor was characterized by having bimodal distribution of chromosome numbers: one at hypodiploid and another at hypotetraploid ranges. Based on comparison of karyotypes between the hypodiploid and hypotetraploid cells, the former was suggested to be developed primarily and the latter by duplication of the hypodiploid karyotype. Malignant transformation of this tumor was assumed to be due to the occurrence of monosomics in some chromosome pairs. Although only 2 per cents of the tumor cells were eudiploid so far they were maintained in in vitro culture, the cell population changed markedly to an eudiploid mode (88%) after storage in deep freezing (-80°C). This phenomenon was explained due to the fact that the diploid cells had a more resistance to the hostile condition than the other cells with altered karyotypes.

Does 8-Azaguanine induce or select for chromosome number instability in human cell hybrids?

Segregant clones resistant to 8-Azaguanine (8AG) obtained from hybrids between clonal derivatives of the EUE line were analysed for chromosome number distribution. In almost all cases the 8AG R clones show chromosome losses and a greater variability in chromosome numbers than that of the parental hybrids and their non-selected subclones. A study of the karyotypic evolution of 8AG R segregant clones maintained for a prolonged period either in 8AG or in drug-free medium did not reveal any correlation between chromosome variability and the presence of 8AG. The preadaptive nature of the segregation to 8AG resistance is also indicated by the results of a fluctuation test.

CHROMOSOME NUMBERS OF NORTH AMERICAN SPECIES OF ANTENNARIA GAERTNER (ASTERACEAE: INULEAE)

Chromosome numbers are presented for 99 populations of 13 species of Antennaria, including A. plantaginifolia, A. neglecta, A. virginica, A. solitaria, A. racemosa, A. corymbosa. A. rosea, A. media, A. Parlinii, A. fallax, A. neodioica, A. canadensis, and A. petaloidea. Four species from the eastern United States (A. plantaginifolia, A. neglecta, A. solitaria, and A. virginica) were determined as diploid (n = 14), and these are all sexual. Diploid counts were also obtained for two sexual species (A. racemosa and A. corymbosa) from the western United States. Chromosome counts are presented for two heteroploid agamic complexes occurring in the eastern United States; these include what have traditionally been referred to as A. Parlinii, A. fallax, A. neodioica, A. canadensis, and A. petaloidea. Determinations of 2n = 56, 70, 84, and 112 were obtained for the A. Parlinii and A. fallax groups, where 2n = 84 had been the only number previously reported. Numbers of 2n = 84 were confirmed for A. petaloidea and A. canadensis and 2n = 56 for A. neodioica. The western United States polyploid species (A. rosea and A. media) are reported as 2n = 56. The presence of apomixis is correlated with polyploidy. The distribution of chromosome numbers in eastern United States Antennaria demonstrates that two diploids and many polyploids occur above the glacial margin, and thus there is an increase in the frequency of polyploidy with latitude. Colonization of the glaciated region by Antennaria following the recession of the Wisconsin ice sheet is also discussed. Many of the polyploids occur only in the glaciated region, thus suggesting a recent origin for these cytotypes. There is evidence indicating that the original base number in Antennaria may be x = 7.