Division Of Meiosis Research Articles

The role of meiotic cohesin REC8 in chromosome segregation in γ irradiation-induced endopolyploid tumour cells

Escape from mitotic catastrophe and generation of endopolyploid tumour cells (ETCs) represents a potential survival strategy of tumour cells in response to genotoxic treatments. ETCs that resume the mitotic cell cycle have reduced ploidy and are often resistant to these treatments. In search for a mechanism for genome reduction, we previously observed that ETCs express meiotic proteins among which REC8 (a meiotic cohesin component) is of particular interest, since it favours reductional cell division in meiosis. In the present investigation, we induced endopolyploidy in p53-dysfunctional human tumour cell lines (Namalwa, WI-L2-NS, HeLa) by gamma irradiation, and analysed the sub-cellular localisation of REC8 in the resulting ETCs. We observed by RT-PCR and Western blot that REC8 is constitutively expressed in these tumour cells, along with SGOL1 and SGOL2, and that REC8 becomes modified after irradiation. REC8 localised to paired sister centromeres in ETCs, the former co-segregating to opposite poles. Furthermore, REC8 localised to the centrosome of interphase ETCs and to the astral poles in anaphase cells where it colocalised with the microtubule-associated protein NuMA. Altogether, our observations indicate that radiation-induced ETCs express features of meiotic cell divisions and that these may facilitate chromosome segregation and genome reduction.

Development of juman male meiosis in vitro.

Testes material from 16 men was used to study the development of human meiosis in vitro. The present report deals with the results from the analysis of the cells from the organ cultures of five of these men. H3-thymidine was added to the culture medium for 75 to 90 minutes. The isotope was removed and the cells were thoroughly washed in 3 changes of fresh medium without tritium. Subsequently they were incubated at 36°C for 14 days. Feulgen squashes and sections were prepared and labelled cells were photographed. After this procedure the silver grains were removed from the autoradiographs in order to identify the meiotic stages. The most advanced stages found labelled, after the cells had been in culture for 14 days, were the following: prometaphase I, metaphase I, prophase II and telophase II. Under the culture conditions used human spermatocytes are able to develop in vitro from DNA synthesis to the end of the second division of meiosis.

A Misclassification Model for the Non‐Disjunction Fraction in Meiosis I

In this paper we introduce a misclassification model for the meiosis I non-disjunction fraction in numerical chromosomal anomalies named trisomies. We obtain posteriors, and their moments, for the probability that a non-disjunction occurs in the first division of meiosis and for the misclassification errors. We also extend previous works by providing the exact posterior, and its moments, for the probability that a non-disjunction occurs in the first division of meiosis assuming the model proposed in the literature which does not consider that data are subject to misclassification. We perform Monte Carlo studies in order to compare Bayes estimates obtained by using both models. An application to Down Syndrome data is also presented.

ADP-Ribosylation Factor 1 Regulates Asymmetric Cell Division in Female Meiosis in the Mouse1

Mouse oocytes undergo two successive meiotic divisions to generate one large egg with two small polar bodies. The divisions are essential for preserving the maternal resources to support embryonic development. Although previous studies have shown that some small guanosine triphosphatases, such as RAC, RAN, and CDC42, play important roles in cortical polarization and spindle pole anchoring, no oocytes undergo cytokinesis when the mutant forms of these genes are expressed in mouse oocytes. Here, we show that the ADP-ribosylation factor 1 (ARF1) plays an important role in regulating asymmetric cell division in mouse oocyte meiosis. Microinjection of mRNA of a dominant negative mutant form of Arf1 (Arf1(T31N)) into fully grown germinal vesicle oocytes led to symmetric cell division in meiosis I, generating two metaphase II (MII) oocytes of equal size. Subsequently, the two MII oocytes of equal size underwent the second round of symmetric cell division to generate a four-cell embryo (zygote) when activated parthenogenetically or via sperm injection. Furthermore, inactivation of mitogen-activated protein kinase (MAPK) but not MDK (also known as MEK) has been discovered in the ARF1 mutant oocytes, and this further demonstrated that ARF1, MAPK pathway plays an important role in regulating asymmetric cell division in meiosis I. Similarly, ARF1(T31N)-expressing, superovulated MII oocytes underwent symmetric cell division in meiosis II when activation was performed. Rotation of the MII spindle for 90 degrees was prohibited in ARF1(T31N)-expressing MII oocytes. Taken together, our results suggest that ARF1 plays an essential role in regulating asymmetric cell division in female meiosis.

Dbf4-Dependent Cdc7 Kinase Links DNA Replication to the Segregation of Homologous Chromosomes in Meiosis I

Meiosis differs from mitosis in that DNA replication is followed by the segregation of homologous chromosomes but not sister chromatids. This depends on the formation of interhomolog connections through crossover recombination and on the attachment of sister kinetochores to microtubules emanating from the same spindle pole. We show that in yeast, the Dbf4-dependent Cdc7 kinase (DDK) provides a link between premeiotic S phase, recombination, and monopolar attachment. Independently from its established role in initiating DNA replication, DDK promotes double-strand break formation, the first step of recombination, and the recruitment of the monopolin complex to kinetochores, which is essential for monopolar attachment. DDK regulates monopolin localization together with the polo-kinase Cdc5 bound to Spo13, probably through phosphorylation of the monopolin subunit Lrs4. Thus, activation of DDK both initiates DNA replication and commits meiotic cells to reductional chromosome segregation in the first division of meiosis.

Regulation of APC/C Activators in Mitosis and Meiosis

The anaphase-promoting complex/cyclosome (APC/C) is a multisubunit E3 ubiquitin ligase that triggers the degradation of multiple substrates during mitosis. Cdc20/Fizzy and Cdh1/Fizzy-related activate the APC/C and confer substrate specificity through complex interactions with both the core APC/C and substrate proteins. The regulation of Cdc20 and Cdh1 is critical for proper APC/C activity and occurs in multiple ways: targeted protein degradation, phosphorylation, and direct binding of inhibitory proteins. During the specialized divisions of meiosis, the activity of the APC/C must be modified to achieve proper chromosome segregation. Recent studies show that one way in which APC/C activity is modified is through the use of meiosis-specific APC/C activators. Furthermore, regulation of the APC/C during meiosis is carried out by both mitotic regulators of the APC/C as well as meiosis-specific regulators. Here, we review the regulation of APC/C activators during mitosis and the role and regulation of the APC/C during female meiosis.

An uncommon H3/Ser10 phosphorylation pattern inCestrum strigilatum(Solanaceae), a species with B chromosomes

Cestrum strigilatum (Solanaceae) is a South American shrub with B chromosomes. Bs show a univalent behavior when a single B is present, have non-Mendelian segregation, and are poor in genes and rich in repetitive DNA. In this study, the histone H3 at serine 10 (H3/Ser10) phosphorylation pattern was investigated during mitosis and meiosis of C. strigilatum collected from the wild and was compared in A and B chromosomes. The results revealed that H3/Ser10 phosphorylation of A chromosomes occurred only in the pericentromeric region in both mitosis and meiosis, whereas in the B univalent, phosphorylation appeared in almost the whole extent of the chromosome, except in the terminal portion of the long arm. In meiosis II, the phosphorylation of A chromosomes was similar to that in the first division of meiosis, but the Bs did not show H3/Ser10 phosphorylation. Our results suggest that phosphorylation at the pericentromeric region may be associated with chromosome motility during cell divisions and with the cohesion of B chromatids in a univalent structure in meiosis I.

ARF1 Determines Asymmetric Cell Division in Oocyte Meiosis.

Mouse oocyte undergoes two successive meiotic divisions and forms one large oocyte with two small polar bodies, which is essential for preserving the maternal complement of resources to support further embryonic development. Several small GTPase proteins, including Ran, Rac and Cdc42, have been found play important roles in meiotic spindle organization, anchoring and polar bodies extrusion. However, little is known about the mechanism of this extremely asymmetric cell division occurred in meiosis. Here we show that the ADP-ribosylation factor 1 (ARF1) is the determinant gene to drive the asymmetric cell division in oocyte meiosis. Microinjection of dominant negative isoform of ARF1 (ARF1T31N) mRNA into fully grown germinal vesicle oocytes led to symmetric cell division in meiosis I. Two metaphase II oocytes with equal size were generated from one single oocyte and arrested at M-phase. The similar phenomenon was observed in meiosis II, ARF1T31N expressed metaphase II oocytes underwent symmetric cell division when the oocytes were activated by either parthnogenetic activation or sperm injection. Furthermore, rotating of the metaphase spindle for 90 degree, which is essential for extruding small polar bodies, was prohibited in ARF1T31N mRNA injected oocytes, which might account for the symmetric cell division occurred in ARF1 mutant oocyte. Together, our results indicated that ARF1 plays critical role in determining asymmetric cell division in female meiosis. [Supported by National High Technology Project 863 (2005AA210930)]

RAPD and Cytogenetic Study in F1 and F2 of Interspecific Cross between Gossypium arboreum*Gossypium anomalum

An interspecific hybrid between G. arboreum×G. anomalum was obtained by pollinating previous day bagged flowers of G. arboreum genetic male sterile line MPKV GMS with pollen from wild G. anomalum.The chromosome constitution in all the plants of G. arboreum and G. anomalum were found to be normal while interspecific hybrid showed mean chromosome association 1.081I+10.479II+0.000III+0.990IV with normal sporads. Interspecific hybrid showed anomalous behavior of univalent and formation of single and double chromatin bridges both during fist and second meiotic division of meiosis. Meiotic chromosome association was observed in nine plants of F2 generation. The cytological studies showed that F1 and F2 generations were having irregular pairing and unequal separation of chromosomes. This led to pollen sterility in these generations. In F2 plants some good plants identified with higher pollen fertility and more number of bolls per plant. Selections from these plants can help to introgress desired characters from G. anomalum to G. arboreum. Random Amplified Polymorphic DNA (RAPD) analysis was employed to characterize the F1 interspecific hybrid of G. arboreum MPKV GMS×G. anomalum and its nine segregants. A total fifteen primers of 10 mer were screened of which eight were selected based on polymorphism of amplified fragments, amplification intensity and the presence of informative markers. Maximum 98 amplified fragments were resolved on the gel for parents, F1 and F2's with OPC-19 primers, whereas, minimum 25 fragments were seen with OPD-04 primer. Similarity coefficient based on DNA amplification using amplified RAPD primer was estimated. The values for genetic similarity ranged from 0.14 to 0.77.

Seed set and some cytological characters in different generations of autotetraploid perennial rye (Secale montanum Guss)

Artificial autotetraploids of diploid perennial rye (Secale montanum Guss) plants were obtained by colchicine treatment. C1 C2 and C3 generations of autotetraploid perennial rye were compared for seed set and cytological characteristics such as irregularities in metaphase I (univalents) and anaphase I and II (lagging chromosomes and/or chromatids and bridge formation) and micronuclei in tetrads. In the three generations (C1 C2 and C3) the percentage of cells with univalents was 18.51, 14.56 and 9.38% respectively. The percentage of cells with irregular anaphase I with univalents was 23.43, 15.93 and 7.85%, and for anaphase II cells it was 20.93, 16.47 and 7.16. The percentage of tetrads with micronuclei was 18.17, 14.07 and 6.17% and seed set was 27.72, 43.51 and 59.59% respectively. A negative correlation was found between seed set and the cytological characteristics investigated. The correlations among the characters investigated during meiosis division were statistically significant. Selection of vigorous plants of autotetraploid perennial rye increased seed setting by increasing the cytological balance. However, abnormalities in the early stage of meiosis division were reflected in the later stages of meiosis.

What Did Sutton See?: Thirty Years of Confusion Over the Chromosomal Basis of Mendelism

IN December 1902, 2 years after the rediscovery of Mendel's 1865 article, America's leading cytologist, Edmund Beecher Wilson, announced to the readers of Science that a graduate student of his at Columbia University had discovered the physical basis of the “Mendelian principle,” by which Wilson meant the segregation of Mendelian factors (Wilson 1902). In an article published the following year, which became a classic of genetics, this student, Walter Stanborough Sutton, explained how the behavior of chromosomes during meiosis—as he interpreted it in his observations of spermatogenesis of the grasshopper Brachystola magna—could explain not only Mendelian segregation but also Mendelian assortment. Sutton had done much of the cytological work as a student of Clarence Erwin McClung at the University of Kansas, but his interpretation of his results in light of Mendelism was done at Columbia. Supposing that Mendel's factors were located on chromosomes, he realized that the “association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division [of meiosis]” could explain Mendelian segregation (Sutton 1902, p. 39) and that Mendelian factors on different chromosomes would assort independently if, at the division in which paternal and maternal chromosomes separate “any chromosome pair may lie with maternal or paternal chromatid indifferently toward either pole irrespective of the positions of other pairs” (Sutton 1903, p. 234). Although Sutton's conclusions gained general acceptance only gradually (Morgan 1910; Bateson 1922), his brilliant insight brought cytology and genetics together, initiating the long path of discovery leading to the present understanding of the chromosomal basis of inheritance. Although correct in its essentials, Sutton's analysis contained a critical flaw. As did others at the time, Sutton identified the wrong division of meiosis as the reducing division, the division in which paternal and maternal chromosomes separate. Sutton thought that the separation of paternal and maternal chromosomes and their independent assortment take place during the second meiotic division, while actually they (or, more precisely, their centromeres2) separate and independently assort at the first division. Estella Eleanor Carothers, who in 1913 presented the first clear cytological evidence for the independent assortment of chromosomes, nevertheless perpetuated Sutton's misconception. Carothers followed Sutton as a student of McClung at the University of Kansas and, like Sutton, studied spermatogenesis in Brachystola. Examining slides that Sutton had left behind as well as those she and McClung prepared, Carothers correctly described the segregation and independent assortment of certain recognizable chromosomes in the first division of meiosis. Nevertheless, she supposed that segregation and assortment take place in the second division for all other chromosomes. Confusion over which of the two meiotic divisions was reductive would linger for another 20 years. Despite histories of genetics crediting Sutton for explaining the chromosomal basis of Mendelism, no single work marks the clarification of the understanding of the meiotic divisions. Instead, clarification came from the gradual accumulation and integration of cytological and genetic observations over more than a quarter of a century.

Hop2/Mnd1 acts on two critical steps in Dmc1-promoted homologous pairing

Meiotic recombination between homologous chromosomes ensures their proper segregation at the first division of meiosis and is the main force shaping genetic variation of genomes. The HOP2 and MND1 genes are essential for this recombination: Their disruption results in severe defects in homologous chromosome synapsis and an early-stage failure in meiotic recombination. The mouse Hop2 and Mnd1 proteins form a stable heterodimer (Hop2/Mnd1) that greatly enhances Dmc1-mediated strand invasion. In order to elucidate the mechanism by which Hop2/Mnd1 stimulates Dmc1, we identify several intermediate steps in the homologous pairing reaction promoted by Dmc1. We show that Hop2/Mnd1 greatly stimulates Dmc1 to promote synaptic complex formation on long duplex DNAs, a step previously revealed only for bacterial homologous recombinases. This synaptic alignment is a consequence of the ability of Hop2/Mnd1 to (1) stabilize Dmc1-single-stranded DNA (ssDNA) nucleoprotein complexes, and (2) facilitate the conjoining of DNA molecules through the capture of double-stranded DNA by the Dmc1-ssDNA nucleoprotein filament. To our knowledge, Hop2/Mnd1 is the first homologous recombinase accessory protein that acts on these two separate and critical steps in mammalian meiotic recombination.

Ultrastructure and development of the megagametophyte in Eleusine tristachya (Lam.) Lam. (Poaceae)

Eleusine tristachya (Lam.) Lam. is native from subtropical South American climates. Widespread in Argentina and Uruguay, it is frequently found in landscape prairies of the province of Buenos Aires. Megasporogenesis and megagametogenesis in this species were studied using light and transmission microscopy. The ovule is hemitropous, bitegmic and tenuinucellate. The megaspore mother cell enlarges and undergoes meiosis division resulting in a T-shaped tetrad of megaspores. The three micropylar megaspores degenerate, and the chalazal one develops into the Polygonum-type megagametophyte. The synergid cells have the cytoplasm very electron dense because it has got a rich complement of organelles. The synergid wall is strongly thickened at the micropylar pole, developing the filiform apparatus. At maturity, the antipodals originate a wall with large projections into the cytoplasm, acquiring transfer cells characteristics. The antipodals cytoplasm, enriched with organelles shows a high metabolic activity, and it is suggested that these cells perform as an efficient system for metabolites transport.

Single Holliday Junctions Are Intermediates of Meiotic Recombination

Crossing-over between homologous chromosomes facilitates their accurate segregation at the first division of meiosis. Current models for crossing-over invoke an intermediate in which homologs are connected by two crossed-strand structures called Holliday junctions. Such double Holliday junctions are a prominent intermediate in Saccharomyces cerevisiae meiosis, where they form preferentially between homologs rather than between sister chromatids. In sharp contrast, we find that single Holliday junctions are the predominant intermediate in Schizosaccharomyces pombe meiosis. Furthermore, these single Holliday junctions arise preferentially between sister chromatids rather than between homologs. We show that Mus81 is required for Holliday junction resolution, providing further in vivo evidence that the structure-specific endonuclease Mus81-Eme1 is a Holliday junction resolvase. To reconcile these observations, we present a unifying recombination model applicable for both meiosis and mitosis in which single Holliday junctions arise from single- or double-strand breaks, lesions postulated by previous models to initiate recombination.

Chemical Inactivation of Cdc7 Kinase in Budding Yeast Results in a Reversible Arrest That Allows Efficient Cell Synchronization Prior to Meiotic Recombination

Genetic studies in budding yeast have provided many fundamental insights into the specialized cell division of meiosis, including the identification of evolutionarily conserved meiosis-specific genes and an understanding of the molecular basis for recombination. Biochemical studies have lagged behind, however, due to the difficulty in obtaining highly synchronized populations of yeast cells. A chemical genetic approach was used to create a novel conditional allele of the highly conserved protein kinase Cdc7 (cdc7-as3) that enables cells to be synchronized immediately prior to recombination. When Cdc7-as3 is inactivated by addition of inhibitor to sporulation medium, cells undergo a delayed premeiotic S phase, then arrest in prophase before double-strand break (DSB) formation. The arrest is easily reversed by removal of the inhibitor, after which cells rapidly and synchronously proceed through recombination and meiosis I. Using the synchrony resulting from the cdc7-as3 system, DSB-dependent phosphorylation of the meiosis-specific chromosomal core protein, Hop1, was shown to occur after DSBs. The cdc7-as3 mutant therefore provides a valuable tool not only for understanding the role of Cdc7 in meiosis, but also for facilitating biochemical and cytological studies of recombination.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3-5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3–5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

Dual Role of the Cdc7-regulatory Protein Dbf4 during Yeast Meiosis

The Dbf4-dependent Cdc7 kinase (DDK) is essential for chromosome duplication in all eukaryotes, but was proposed to be dispensable for yeast pre-meiotic DNA replication. This discrepancy led us to investigate the role of the unstable Cdc7-regulatory protein Dbf4 in meiosis. We show that, when Dbf4 is depleted at the time of meiotic induction, cells enter the meiotic program but do not replicate their chromosomes. Surprisingly when Dbf4 is depleted after the initiation of DNA synthesis, S phase goes to completion, but most cells arrest before anaphase I. Deletion of the cohesin Rec8 suppresses this phenotype, suggesting a distinct role of DDK for meiotic chromosome segregation. As after Cdc5 depletion, a fraction of cells undergo a single equational division suggesting a failure to mono-orient sister kinetochores. Our results demonstrate that Dbf4 is essential for DNA replication during meiosis like in vegetative cells and provide evidence for an additional role in setting up the reductional division of meiosis I.

The presence of cumulus cells on nuclear maturation of sheep oocytes during in vitro maturation

This study was carried out to investigate the role of maturation by cumulus cells and the initial bond between the cumulus cells and the oocyte on nuclear maturation of sheep oocytes. Ovaries collected from the local abattoir were transported to the laboratory in saline at 30–35 °C within 1–3 h after collection. The oocytes of follicles, 2–6 mm in diameter, were recovered by aspiration and collected in a pre-incubated (at 38.6 °C, 5% CO 2, and 100% humidity) Hepes-modified TCM 199 medium. After preliminary evaluation, the oocytes with evenly granulated cytoplasm and which were surrounded with at least two layers of cumulus cells (good quality oocytes) were selected and subjected to culture in pre-incubated bicarbonate-buffered TCM 199 supplemented with 0.05 IU/ml recombinant human follicle stimulating hormone (rhFSH), 1 IU/ml human chorionic gonadotropin (hCG), and 1 μg/ml estradiol (OCM: oocyte culture medium). Before culturing, the selected oocytes were randomly divided into four treatment groups: Group 1, cumulus enclosed oocytes cultured in OCM; Group 2, denuded oocytes cultured in OCM; Group 3, denuded oocytes co-cultured with a cumulus cell monolayer in OCM; Group 4, denuded oocytes cultured in OCM in the presence of cumulus cells-conditioned medium. After an incubation period (26–27 h), the nuclear status of the oocytes in each treatment group was assessed using a 2% orcein stain. The rate of oocytes reaching the metaphase II (MII) stage (metaphase of second stage of meiosis division) was 82%, 5%, 11%, and 47% for Groups 1, 2, 3, and 4, respectively. The differences between groups were significantly ( P < 0.05) different. The percentage of MII oocytes in Group 4 (47%) was higher than that obtained in Group 3 (11%), indicating a higher efficiency in a cumulus cell-conditioned medium, compared to the cumulus cells monolayer in providing the proper condition for sheep oocyte nuclear maturation. The results suggest the ability of sheep oocytes to resume meiosis in the absence of gap junctional communication (GJC) between the cumulus cells and oocyte being drastically interrupted while for optimum oocyte nuclear maturation, the intact physical contact between the oocyte and cumulus cells is essential.

Genetic analysis of the position of meiosis in Porphyra haitanensis Chang et Zheng (Bangiales, Rhodophyta)

Crossing experiments were carried out between artificial pigmentation mutants and the wild type in Porphyra haitanensis Chang et Zheng to ascertain where meiosis occurs in its life history by confirming whether the color segregation and the color-sectored blades appear in F1 gametophytic blades developed from conchospores which are released from heterozygous conchocelis. Two red-type pigmentation mutants (R-10 and SPY-1) were used as the female parent. Their blades are red or red orange in color, thinner than the wild type and weak in elasticity, and have no denticles on their margins. The wild type (W) was used as the male parent; its blades are light brown in color, thick and good in elasticity, and have many marginal denticles. The F1 gametophytic blades developed from conchospores which were released from heterozygous conchocelis produced in the crosses of R-10(♀)×W(♂) and SPY-1(♀)×W(♂) showed two parental colors (R and W) and two new colors (R', lighter in color than R; W', wild-type-like color and redder than W). Linear segregation of colors occurred in the F1 blades, forming color-sectored blades with 2–4 sectors. In the color-sectored blades, R and R' sectors were thinner than W and W' sectors, and had weak elasticity and no denticles on their margins, whereas W and W' sectors were thick and had good elasticity and many marginal denticles. Of the F1 gametophytic blades, 95.2–96.7% were color-sectored and only 3.3–4.8% were unsectored. These results indicate that meiosis of P. haitanensis occurs during the first two cell divisions of a germinating conchospore, and thus it is considered that the initial four cells of a developing conchosporeling constitute a linear genetic tetrad leading to the formation of a color-sectored blade. The new colors of R' and W' were recombinant colors due to the chromosome recombination during the first cell division in meiosis. It is considered that color phenotypes of the two mutants used in this paper were result of two (or more) recessive mutations in different genes, and that they also have mutations concerned with blade thickness and formation of marginal denticles, which are linked with the color mutations.