What is the difference between meiosis and mitosis yahoo answers

There are 2 divisions, meiosis I and meiosis II. What happens in prophase I? Chromosomes condense, nuclear envelope breaks down, homologous chromosomes pair up and cross over.

What is crossing over, when does it occur, and why is it important? Occurs in prophase, one portion of each chromatid is exchanged, causes genetic recombination.

What happens in metaphase I Homologous chromosomes move to the middle of the cell. When does the cell go from diploid to haploid? Anaphase I or telophase I of meiosis I. What happens in telophase I? Chromosomes gather at poles, nuclear envelope forms, cytoplasm divides.

At the end of meiosis I, how many cells are there and are they haploid or diploid? What happens during metaphase II? Chromosomes align in center, spindle fibers attach to centromeres. What happens during anaphase II? Centromere divides, chromatids move to opposite poles.

What happens during telophase II? What is independent assortment and why is it important? Each pair of chromosomes separate independently; causes multiple gametes to be produced. What is random fertilization and why is it important? A lot of different possibilities for the gamete combination of the zygote. What is the difference between anaphase I and anaphase II? Anaphase I separates homologous chromosomes; anaphase II separates chromatids. How many parents are needed for this process to occur?

Process by which organisms produce more of their own kind; 2 parents. What is that diploid cell called? Are the cells Haploid or Diploid?

Exact duplication of nucleus to form 2 identical nuclei; diploid. Give an example of an organism that reproduces this way. What part of the cell is smaller than the parent in this process? New individuals split off from the parent the bud is the part that splits off. Unfertilized eggs develop into new individuals. What parts can a new plant develop from? Asexual Advantage: produce a lot of offspring in short period of time without a mate Disadvantage: DNA does not vary.

Sexual advantage: makes different combinations of genes Disadvantage: individuals have to find a mate. Buka menu navigasi. Tutup saran Cari Cari. Pengaturan Pengguna. Lewati carousel. Karusel Sebelumnya. Karusel Berikutnya. Apa itu Scribd? Study Guide Answers. Diunggah oleh misterbrowner. Apakah menurut Anda dokumen ini bermanfaat? Apakah konten ini tidak pantas? Laporkan Dokumen Ini. Tandai sebagai konten tidak pantas.

Unduh sekarang. Judul terkait. Karusel Sebelumnya Karusel Berikutnya. Lompat ke Halaman. Cari di dalam dokumen. Meiosis 2. There are 2 divisions, meiosis I and meiosis II 4. Chromosomes condense, nuclear envelope breaks down, homologous chromosomes pair up and cross over 5. Occurs in prophase, one portion of each chromatid is exchanged, causes genetic recombination 6. What happens in metaphase I Homologous chromosomes move to the middle of the cell 7.

What happens in anaphase I? Homologous chromosomes separate 8. Addition of the inhibitor at 5 hours completely prevented both the modification and nuclear localisation of Clb1 Figure 3A and 3B. These results indicate that Clb1 modification and nuclear localisation are dependent on CDK but not Ime2 activity. Samples were taken hourly from 5 hours onwards for whole cell extracts and for in situ immunofluorescence. Whole cell extracts were analysed by Western blotting using anti-myc and anti-tubulin antibodies.

Localization of Clb1 was assayed by in situ immunofluorescence green-nuclear, red-cytoplasmic, blue-no signal. Data for additional time points are indicated in the Figure S3.

CDK is not meiosis-specific; to explain the meiosis-specific nature of the phosphorylation, another regulatory step must be involved.

Cdc5 is also active during meiosis and has a number of meiosis-specific functions [30] , [31]. Cdc5 expression also coincides with Clb1 phosphorylation Figure S3.

The requirement for Cdc5 activity was examined by depleting Cdc5 in meiosis by replacing the endogenous promoter with that of CLB2. This also shows that Clb1 nuclear localisation is independent of its phosphorylation. Since Cdc5 is required for exit from meiotic prophase [31] , our results also indicate that exit from prophase is not required for nuclear localisation of Clb1. A Samples were taken hourly throughout the time course for in situ immunofluorescence to determine Clb1 localisation green-nuclear, red-cytoplasmic, blue-no signal.

B Samples were taken hourly from 4 hours for preparing whole cell extracts. Whole cell extracts were analysed by Western blotting using anti-myc Clb1 , anti-Cdc5 and anti-tubulin antibodies. Asterisk represents a cross-reactive band seen in anti-Cdc5 blots. In each case, two sequences were added in tandem to overcome any endogenous localisation signals Figure 5A. A Schematic showing the variants of Clb1 constructed to alter its nuclear localization.

Clb1 localization was determined by immunofluorescence. Samples were taken hourly to determine Clb1 localisation. To determine the effect of altering nuclear localization of cyclin Clb1 during meiosis, we induced wild type and nuclear localization mutant strains to enter meiosis and examined nuclear division and Clb1 phosphorylation Figure 6A—C. These results concur with the idea that nuclear import of Clb1 is a prerequisite for its modification during meiosis I.

We therefore propose that Clb1 is imported to the nucleus by a meiosis-specific mechanism, and phosphorylated in a Cdc5-dependent manner upon nuclear entry. Nuclear division in the three cultures was determined by DAPI staining and the data are represented graphically.

Whole cell extracts were analysed by Western blotting for Clb1 phosphorylation. Samples were taken at time 0 and hourly from 4—10 hours for whole cell extracts and analysed by Western blotting. Activation of FEAR during meiosis I but not during mitosis is sufficient to cause disassembly of anaphase spindles.

The mutant cells undergo two divisions on the same spindle forming dyads. This is consistent with the possibility that increased nuclear localization of Clb1 promotes FEAR activation during meiosis I. Percentage of cells forming dyads, tetrads and monads were calculated after 48 h.

Nucleolar separation in cells containing anaphase I and metaphase II spindles was assayed by immunofluorescence. Representative images of cells are shown on the right. C Data obtained in B are presented graphically. E Sample images of cells with nucleolar Cdc14 or Cdc14 released are shown on the right. To determine whether increased nuclear localization of Clb1 promotes efficient activation of FEAR, we compared the kinetics of nucleolar separation in wild type and nuclear localization mutants of CLB1.

We quantified nucleolar splitting in cells with either anaphase I or metaphase II spindles. This is consistent with the idea that nuclear localization of Clb1 increases the efficiency of FEAR activation. This supports the idea that the meiosis-specific nuclear localization of Clb1 amplifies FEAR activation. However the NES-tagged Clb1 had little effect on the kinetics of Cdc14 release and nucleolar division.

Taken together our results are consistent with the hypothesis that increased nuclear localization of Clb1 enhances activation of FEAR during meiosis I. Phosphorylation and nuclear localization of Clb1 during meiosis in budding yeast has been previously reported [22] , [23]. However the functional significance of these observations and the mechanistic correlation between the two events, if any, was not known. In this paper, we demonstrate that phosphorylation and nuclear localization of Clb1 do not occur during mitosis and are therefore meiosis-specific.

Phosphorylation of Clb1 requires its localization to the nucleus but not vice versa. Altering Clb1 localisation during meiosis did not lead to a loss of sporulation efficiency or viability in otherwise wild-type backgrounds, implying that Clb1 localisation is not essential for successful meiosis.

Functional redundancy amongst B-cyclins could mask the effects of altering Clb1 nuclear localization. However the synthetic effects observed with FEAR mutants suggests that Clb1 nuclear localization contributes to efficient exit from meiosis I. Our data support the idea that Clb1 localisation to the nucleus might amplify FEAR activation during exit from meiosis I and cause disassembly of anaphase I spindles.

Increased nuclear localization of Clb1 could result in enhanced access to its nucleolar substrate Net1. Moreover Clb1's nuclear localization is unaffected by premature activation of Cdc14 Figure 1B and therefore phosphorylation of Net1 could proceed at an increased rate compared to mitotic anaphase despite FEAR activation. Mutations in genes encoding two karyopherins Mtr and Srp1 suppress the null phenotype of MEN mutants [35]. It will be interesting to test whether these karyopherins regulate nuclear localization of Clb1 during meiosis I.

Our work raises a number of interesting questions. How Clb1 is transported to the nucleus during meiosis I? What is the functional significance of Clb1 phosphorylation? How is Clb1 phosphorylation and nuclear localization reversed after meiosis I? Answers to these questions might help in understanding how meiotic yeast cells modulate their CDK activity to undergo two rounds of nuclear division without an intervening S-phase.

Nuclear division in CLB1-myc 9 cells. Samples were taken for in situ immunofluorescence hourly and nuclear division was scored by DAPI staining. Kinase activity of Ime2 is not required for nuclear localization and phosphorylation of Clb1.

Blots were also probed with anti-myc to detect Ime2 and anti-tubulin antibody. CDK activity is required for Clb1 phosphorylation and nuclear localization. Samples were taken hourly from 5 hours for whole cell extracts A and hourly throughout the time course for imaging B.

A Immunoprecipitated Clb1 from the three cultures was detected by western blotting. B Purified Clb1 was incubated with 3. List of yeast strains. All yeast strains used are derivatives of SK1 and have the following markers, unless otherwise stated stated. The strains used for experiments described in the Main and Supplementary figures are listed in Table 1A and 1B respectively.

Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Cyclin-dependent kinases CDK are master regulators of the cell cycle in eukaryotes. Introduction Meiosis is a specialised form of cell division required for sexual reproduction, in which a diploid cell divides to form four haploid gametes.

Materials and Methods The genotypes of all strains used in the experiments are listed in Table S1. Immunoprecipitation of Clb1 For meiotic samples, 25 ml samples of cell cultures at OD of 3 were used.

Results Clb1 modification and nuclear localisation is specific to metaphase I of meiosis Clb1 has been observed to be post-translationally modified and localized to the nucleus during meiosis I [22] , [23]. Download: PPT. Figure 1. Clb1 is phosphorylated and localizes to the nucleus during metaphase I. Figure 2.

Clb1 modification and nuclear localisation are meiosis—specific. CDK and Cdc5 activity are required for Clb1 phosphorylation The meiosis-specific nature of Clb1 phosphorylation led us to consider Ime2 as a candidate kinase. Figure 3. CDK activity is required for Clb1 phosphorylation and nuclear localization during meiosis I. Cdc5 activity is required for Clb1 modification but not nuclear localization CDK is not meiosis-specific; to explain the meiosis-specific nature of the phosphorylation, another regulatory step must be involved.

Figure 4. Cdc5 is required for phosphorylation, but not nuclear localisation, of Clb1 during meiosis I. Figure 5. Figure 6. Phosphorylation of Clb1 during meiosis requires its localization to the nucleus. Figure 7. Discussion Phosphorylation and nuclear localization of Clb1 during meiosis in budding yeast has been previously reported [22] , [23]. Supporting Information. Figure S1. Figure S2. Figure S3. Figure S4. Table S1. References 1. Cell Mol Life Sci — View Article Google Scholar 2. Cell — View Article Google Scholar 3.