A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.     

Probing meiosis in hybrids of Lolium (Poaceae) with a discriminatory repetitive genomic sequence

A moderately repetitive genomic DNA sequence (designated pLPBB2-123) derived from Lolium perenne L. (Poaceae) is considerably more abundant in the genome of this species than in that of the closely related L. temulentum. The repetitive sequence probe is clearly able to discriminate between the genomic DNA of both species in Southern analysis, and effectively ’paints’ only the chromosome set of L. perenne in diploid and triploid hybrids with L. temulentum. Fluorescence in situ hybridisation of this sequence onto homoeologous chromosomes during meiosis I of the hybrids shows that the sequence is evenly distributed along all of the chromosomes of L. perenne and appears to have little effect on the structural integrity or recombination potential of hybrid bivalents. Discrimination between chromatin of different parental origin in hybrid bivalents shows for the first time a progressive relaxation of relational coiling of homoeologues throughout meiotic prophase. It also highlights structural irregularities that can now be unequivocally assigned to the longer chromosomes of L. temulentum. The advantages of the use of specific differentially amplified sequences instead of whole genome probes are discussed within the context of introgression breeding programmes within the Lolium/Festuca complex. Received: 14 December 1999; in revised form: 15 February 2000 / Accepted: 15 February 2000     

Chromosome association and pollen fertility of parental and interspecific hybrids of Lycopersicon esculentum X L. hirsutum and L. pennellii

Cytological studies were carried out on two wild species (L. hirsutum and L. pennellii) and the cultivated species (L. esculentum) of tomato and their F1 hybrids. Both parents and hybrids show a diploid chromosome number of 2n=24. The meiotic behaviour of the cultivated species showed a high degree of chromosome homology resulting in a high level of chiasmata frequency per bivalent. In contrast, the two wild species showed a slight increase in uniyalent frequency and a decrease in bivalent formation and chiasmata frequency. The meiotic behaviour of the hybrids showed a high level of univalents and low levels of bivalents as well as trivalents. Highly significant decreases in chiasmata frequency and increases in meiotic abnormalities, especially in the L. esculentum X L. pennellii hybrid, also were detected. The high meiotic irregularity and low chiasmata frequency recorded in the second hybrid indicated the disharmony and difference between its parental genomes and also served to predict its sterility. With regard to degree of pairing recorded in the hybrids, there is a possibility that sterility in such cases may refer to genetic factors in addition to the previously mentioned reasons. Pollen fertility showed no great difference between L. esculentum and L. hirsutum and their F1 hybrid, but a significant decrease was recorded in the L. esculentum X L. pennellii hybrid, which was clearly associated with high meiotic irregularity, low chiasmata frequency and chromosome association.     

THE QUESTION OF POST-REDUCTION IN SPHAGNUM

The 19 spatially distinct chromosomal units at first meiotic metaphase in sporophytically diploid species of Sphagnum have usually been considered to be bivalents, but one investigator (Sorsa, 1956) has interpreted them as chromosomes from dissociated bivalents and meiosis as post-reductional. The present studies on diploid S. squarrosum (Pers.) Crome establish the chromosome number on the basis of the following evidence: there are in addition to m-chromosomes, 19 pairs of chromosomes in early prophase, 19 bivalents at diakinesis, 19 chromosomes in each of the two sets at second metaphase, 19 daughter chromosomes in each of the four sets at late second anaphase, and 19 chromosomes in gametophytic mitoses. The 19 bodies at first meiotic metaphase in diploid species are true bivalents in loose secondary association, which has led to their erroneous interpretation as chromosomes of dissociated bivalents. The gametic chromosome number in sporophytically diploid Sphagnum is therefore, without doubt, n = 19, and this evidence negates the claim for post-reduction in Sphagnum.     

Autosyndetic pairing in Gibasis (Commelinaceae) hybrids revealed by C-banding

Two closely related species of Gibasis, G. karwinskyana and G. consobrina, and their F₁ hybrids were studied cytologically at the diploid and tetraploid level. Despite similarity in their basic karyotype, pairing was extremely limited in the diploid hybrid and almost exclusively autosyndetic in the tetraploid, except for multivalent formation due to interchange heterozygosity. The analysis was considerably facilitated by the use of C-banding techniques at meiosis, by which the chromosomes of each species could be readily identified. In the parents, quadrivalents were formed between homologous but non-identical chromosomes, which also formed autosyndetic bivalents in the hybrids. Meiotic pairing in the hybrids was unaffected by polytypy for C-bands among different populations of the parental species.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

A single dominant gene for Fusarium wilt resistance in protoplast-derived tomato plants

Summary Autotetraploids were established from 8 diploid wild species of section Arachis. In all the autotetraploids the chromosomes paired largely as bivalents even though they possess the ability to pair as multivalents. Pollen and pod fertility in the C₁ generation were not directly associated with chromosome pairing. The C₂ generation autotetraploids showed a gradual increase in bivalent associations and pollen and pod fertility. The identification of two genomes, A and B, in the diploid species and in the tetraploid, A. hypogaea, of the section Arachis, a fairly good crossability, and the type of chromosome associations observed in hybrids between A. hypogaea and the autotetraploids of wild Arachis species indicated good prospects of utilizing autotetraploids as genetic bridges in transferring desired traits from these taxa into groundnut.Submitted as Journal Article No. 516 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Genome relationships between Hordeum vulgare L. and H. bulbosum L.

Interrelationships between H. vulgare (2x=14) and H. bulbosum (2x=14; 4x=28) were estimated on the basis of the karyotypes and the pairing behaviour of the chromosomes in diploid, triploid and tetraploid hybrids obtained with the aid of embryo culture. — A comparison of the karyotypes of the two species revealed similarities as well as differences. It was concluded that at least 4 or more of the chromosomes were similar in morphology and probably closely related. — Diploid and tetraploid hybrids are rarely obtained and their chromosome numbers tend to be unstable whereas triploid hybrids (1 vulgare + 2 bulbosum genomes) were stable and relatively easy to produce. In the diploid hybrid only 40% of the meiotic cells contained 14 chromosomes while the numbers ranged from 7 to 16 in other cells. All hybrids exhibited pairing between the chromosomes of the two species. Diploid hybrids had a mean of 5.0 and a maximum of 7 bivalents per cell in those cells having 14 chromosomes. Triploid hybrids from crosses between 2x H. vulgare and 4x H. bulbosum exhibited a mean of 1.5 and a maximum of 5 trivalents per cell. In a hexaploid sector found following colchicine treatment of a triploid the mean frequencies of chromosome associations per cell were: 5.5_I+8.0_II+0.7_III+3.7_IV+0.3_V+0.4_VI. One unstable 27 chromosome hybrid obtained from crosses between the autotetraploid forms had a mean of 1.1 and a maximum of 4 quadrivalents per cell. The chromosome associations observed in these hybrids are consistent and are taken as evidence of homoeologous pairing between the chromosomes of the two species. Interspecific hybridization between these two species also reveals that chromosome stable hybrids are only obtained when the genomes are present in a ratio of 1 vulgare2 bulbosum. Based upon the results obtained, the possibility of transferring genetic characters from H. bulbosum into cultivated barley is discussed.     

Cytogenetics of the hybrid Gilia millefoliata × achilleaefolia

Summary Gilia millefoliata andG. achilleaefolia, two annual diploid (n=9) species ofPolemoniaceae, crossed readily in certain combinations but not in others. The F₁ hybrids were vigorous but sterile. They gave rise, apparently by the union of unreduced gametes, to an F₂ generation of tetraploids, which were mostly fertile.Chromosome pairing in the hybrids varied markedly according to the state of nutrition of the plants. The F₁ hybrids formed fewer clear diakinesis figures, fewer bivalents, fewer chiasmata per bivalent, and more attenuated or stretched bivalents when grown in 2 pots of sand than when grown in rich soil (Table 3). A pot-bound allotetraploid individual derived from this hybrid showed the same meiotic irregularities as the starved F₁s until irrigated with a solution of mineral nutrients, after which its chromosomes paired regularly in bivalents (Table 2, Fig. 38).The capacity of the F₁ hybrids to produce polyploids also differed strikingly in the two cultures. The rate of polyploidy of the stunted sand-grown hybrids was 2381 viable tetraploid zygotes per million flowers, while the corresponding figure for the luxuriant field hybrids was only 2.7 per million flowers.For the production of polyploid progeny by diploid parents — a process which should be clearly distinguished from normal fertility — the termpolyploidy rate is proposed. It is suggested that starvation of a structural hybrid may sometimes increase its polyploidy rate by reducing chromosome pairing to the point where restitution nuclei and hence unreduced gametes can be formed.     

The effect of B chromosomes on homoeologous pairing in species hybrids

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.     

CHROMOSOMES AND CROSSING BEHAVIOR OF HIBISCUS CANNABINUS,H. ACETOSELLA,AND H. RADIATUS

Menzel , Margaret Y. (Florida State U., Tallahassee), and F. D. Wilson . Chromosomes and crossing behavior of Hibiscus cannabinus, H. acetosella, and H. radiatus. Amer. Jour. Bot. 48(8): 651–657. Illus. 1961.—Chromosomes of diploid H. cannabinus L. (kenaf) form 18 bivalents at metaphase I. In autotetraploid H. cannabinus (2n = 72), more than 50% of the chromosomes pair as trivalents or quadrivalents. In the tetraploid species H. radiatus Cav. and H. acetosella Welw. ex Hiern (H. eetveldeanus De Wild. & Dur.) (2n = 72), only 4% of the chromosomes pair as multivalents and the rest pair as bivalents. Vigorous, highly fertile F₁ hybrids between H. acetosella and H. radiatus are easily obtained, show complete chromosome pairing, and give rise to a freely segregating, vigorous, fertile F₂: apparently the parental species have similar genome constitutions and are closely related. Chromosome pairing in the triploid hybrids of H. radiatus and H. acetosella with H. cannabinus, in hexaploids obtained by doubling the chromosome number of H. acetosella-cannabinus F₁, and in pentaploid and tetraploid backcrosses of the hexaploids to H. cannabinus shows that the tetraploid species each contain 1 genome (A) very similar to, but not identical with, that of H. cannabinus and 1 dissimilar genome (B). Morphology, fertility, and other characteristics of the various hybrids are discussed in connection with the problem of recombining the resistance to root-knot nematodes found in the tetraploid species with the desirable fiber properties of H. cannabinus.     

A novel intergeneric hybrid in the Triticeae: Triticum aestivum x Psathyrost achys juncea

Summary Two hybrid embryos of intergeneric origin between Triticum aestivum cv Fukuho (2n=6x=42, AABBDD) and Psathyrostachys juncea (2n=2x=14, NN) were successfully rescued. One hybrid plant had the expected chromosome number of 28 (ABDN), whereas the second plant had 35 chromosomes. The average meiotic chromosome pairing in the 35-chromosome hybrid was 21.87 univalents + 6.38 bivalents + 0.11 trivalents + 0.009 quadrivalents, which indicates that two copies of the N genome were present. Chromosome pairing in the 28-chromosome hybrid was low (1.35 bivalents), and pointed out the lack of homology between the wheat genomes and the P. juncea genome. These new hybrids showed some necrosis and chlorosis, which caused severe floral abortion in the plant that had 35 chromosomes. These problems became gradually less severe after 18 months.Contrib. no. 372     

Cytological studies on meiosis and male gametophyte development in autotetraploid cucumber

With improved staining and chromosome preparation techniques, meiosis of pollen mother cells (PMCs) and male gametophyte development in autotetraploid cucumber (Cucumis sativus L.) was studied to understand the correlation between chromosomes behaviour and fertility. Various chromosome configurations, e.g. multivalent, quadrivalents, trivalents, bivalents and univalents were observed in most PMCs at metaphase I. Lagging chromosomes were frequently observed at anaphase in both meiotic divisions. In addition, chromosomes segregations were not synchronous and equal in some PMCs during anaphase II and telophase II. Dyads, triads, tetrads with micronuclei and polyads were observed at tetrad stage, and the frequencies of normal tetrad with four microcytes were only 55.4 %. The frequency of abnormal behaviour in each stage of meiosis was counted, and the average value was 37.2 %. The normal meiotic process could be accomplished to form the microspore tetrads via simultaneous cytokinesis. Most microspores could develop into fertile gametophytes with 2 cells and 3 germ pores through the following stages: single-nucleus early stage, single-nucleus late stage and 2-celled stage. The frequency of abnormalities was low during the process of male gametophyte development. The germination rate of pollen grains was 46.9 %. These results suggested that abnormal meiosis in PMCs was the reason for low pollen fertility in the autotetraploid cucumber.     

ARTIFICIAL INTERSPECIFIC HYBRIDIZATION IN RUELLIA (ACANTHACEAE)

Observations were made on the morphology, seed fertility, pollen viability and meiotic configurations of 22 different interspecific hybrids of 12 North American taxa representative of 3 sections of Ruellia. The hybrids were classified as (1) fully vigorous and fertile; (2) vigorous but with reduced fertility; (3) reduced vigor and fertility; (4) weak and sterile. Hybrids showed meiotic irregularities in microsporogenesis: univalents, chains, precocious separation of bivalents, nondisjunction, and micronuclei were commonly observed. Interspecific pollinations within sect. Dipteracanthus resulted in fertile or partially sterile F₁ hybrids. Intersectional crosses produced partially or completely sterile hybrids or failed. Assuming that crossability is correlated with degree of evolutionary relationship, the parental species are interpreted in genecological terms to be grouped in polytypic ecospecies. Hybridization experiments doubtless would be of value in clarifying relationships in tropical and subtropical species of Ruellia.     

Introgression of chromosomes of Festuca arundinacea var. glaucescens into Lolium multiflorum revealed by genomic in situ hybridisation (GISH)

An F₁ hybrid (n=4x=28) between the tetraploid species Festuca arundinacea var. glaucescens (GGG′G′) and a synthetic tetraploid Lolium multiflorum (LmLmLmLm) was backcrossed to diploid L. multiflorum to produce triploid (2n=3x=21) BC₁ hybrids (LmLmG). At metaphase I of meiosis the triploids had a preponderance of ring bivalents and univalents with some linear and frying-pan trivalents. Genomic in situ hybridisation (GISH) differentiated the Festuca chromosomes from Lolium and revealed that the bivalents were exclusively between Lolium homologues, while the univalents were Festuca. Despite the limited amount of homoeologous chiasmata pairing in the triploids, some recombinant chromosomes were recovered in the second backcross when the hybrids were further crossed to diploid L. multiflorum. The progeny from the second backcross was predominantly diploid. Genotypes with recombinant chromosomes and chromosome additions involving an extra Festuca chromosome were identified using GISH. Changes in plant phenotype were related to the presence of Festuca chromatin. Received: 20 September 2000 / Accepted: 05 January 2001     

EXPERIMENTAL HYBRIDS IN EPILOBIUM (INCLUDING SECT. ZAUSCHNERIA) SPECIES WITH N = 15 (ONAGRACEAE)

Experimental hybrids involving the three diploid subspecies of Epilobium sect. Zauschneria formed 15 bivalents at meiotic metaphase I, as did experimental hybrids between the three other species of Epilobium (comprising sect. Cordylophorum) with n = 15. The gametic chromosome number of E. suffruticosum Nutt., n = 15, and its relationship to the other two species are reported for the first time. Although we have not obtained hybrids between the species of these two sections, their morphological similarities are impressive and they are surely closely related.     

Indeterminate meiotic restitution (IMR): a novel type of meiotic nuclear restitution mechanism detected in interspecific lily hybrids by GISH

A detailed analysis of microsporogenesis was carried out in three diploid lily cultivars (2n=2x=24) and three diploid interspecific hybrids (2n=2x=24) using DNA in situ hybridisation methods (GISH and FISH). In cvs. Gelria (Lilium longiflorum; L genome), Connecticut King and Mont Blanc (both Asiatic hybrids; Agenome) meiosis was regular and only haploid gametes were formed while the three interspecific hybrids between L. longiflorum×Asiatic hybrid (LA) showed a variable frequency of meiotic nuclear restitution and stainable 2n-pollen formation ranging from 3% to 30%. An analysis of meiotic chromosome behaviour of the LA hybrids through GISH and FISH revealed that: (1) the parental chromosomes could be clearly discriminated into univalents, half-bivalents and bivalents in the PMCs; (2) in some of the PMCs the entire complement was present either as univalents or half-bivalents which had the potential to divide equationally (following centromere division) during the first division leading to first division restitution (FDR) gametes; (3) more frequently, however, in one and the same PMC the univalents and half-bivalents divided equationally whereas the bivalents disjoined reductionally at the same time giving rise to 2n-gametes that could vary from the well-known FDR or SDR 2n-gametes. We indicate this novel type of restitution mechanism as Indeterminate Meiotic Restitution (IMR). In order to confirm the occurrence of IMR gametes, the chromosome constitutions of eight triploid BC₁ progenies derived from backcrossing the 2n-gamete producing the LAhybrids to the Asiatic hybrid parents were analysed through in situ hybridisation. The results indicated that there were seven BC₁ plants in which FDR 2n-gametes, with or without homoeologous recombinations, were functional, whereas in one case the 2n-gamete resulting from IMR was functional. In the latter, there was evidence for the occurrence of genetic recombination through homoeologous crossing-over as well as through the assortment of homoeologous chromosomes. A singular feature of the IMR 2n-gamete was that although it transmitted a euploid number of 24 chromosomes to the BC₁ progeny, the number of chromosomes transmitted from the two parental species was dissimilar: 9 L-genome chromosomes and 15 A-genome chromosomes instead of 12 of each. Received: 15 May 2000 / Accepted: 4 December 2000     

Cytotypes within the family Umbelliferae with special reference to the genera Seseli L. and Oenanthe L. (subtribe Seselinae)

Cytotypes within the genera Seseli L. and Oenanthe L. show variation in chromosome number in pollen mother cells. A correlation of low chiasma frequency with meiotic irregularities and pollen sterility was noted. In addition to the meiotic irregularities in the two genera occurrence of polyspory and triple pollen formation during meiosis have been observed in Seseli diffusum (Roxb.) Sant. Wagh. The presence of different chromosome numbers in different populations of the same species and karyological investigation in 4 species of Oenanthe L. suggests that structural changes of chromosomes associated with numerical differences have possibly played a role in their evolution. Diminution in chromosome size and complete absence of metacentric chromosomes in Oenanthe lachenalli Gmel. suggest that probably this species is more evolved than 3 species of Oenanthe (i.e., O. benghalensis Benth., O. pimpinelloides L. and O. thomsoni Clarke). The interrelationships of the two genera are discussed.     

GENOME RELATIONSHIPS IN INTERSPECIFIC AND INTERGENERIC HYBRIDS OF RENANTHERA

Kamemoto , H., and K. Shindo . (U. Hawaii, Honolulu.) Genome relationships in interspecific and intergeneric hybrids of Renanthera. Amer. Jour. Bot. 49(7): 737–748. Illus. 1962.—Chromosome numbers and meiotic behavior of species and hybrids of Renanthera (Orchidaceae) were investigated. Renanthera elongata, R. histrionica, R. matutina, R. monachica, and R. storiei were diploid (2n = 38). The race of R. coccinea commonly grown in Hawaii was found to be hexaploid (2n = 114), while a recently introduced clone from Thailand was diploid (2n = 38). Diploid interspecific hybrids formed about 18 bivalents at M-I, indicating a relatively strong homology of parental chromosomes. The tetraploid hybrid of diploid R. monachica and hexaploid R. coccinea showed predominantly 37 or 38 bivalents, indicating good homology of genomes of the 2 parental species, and autosyndetic pairing in the 2 additional genomes of R. coccinea. Intergeneric hybrids involving Renanthera spp. could be classified into 2 distinct groups: those with 14–11 bivalents that are generally oriented at the metaphase plate and eventually lead to a preponderance of tetrads or tetrads with microcytes, and those with fewer bivalents (9–5) many of which are unoriented pseudobivalents and which ultimately give rise to dyads and dyads with microcytes. Relationships of parental species on a taxonomic basis are closer in the former than the latter group.