Mitosis and Meiosis Overview of Mitosis G2 of Interphase • Mitosis produces two Chromatin (duplicated) identical cells – Stages of mitosis – Alignment and separation of chromosomes – Cytokinesis • Meiosis produces DNA replication during Interphase 17 October 2011 Overview of Mitosis Metaphase Anaphase Metaphase plate Daughter chromosomes Metaphase: Chromosomes align in center of cell Anaphase: Sister chromatids separate Spindle fibers shorten at the kinetochore Mark Telophase: Complete set of chromosomes at each pole 3 Chromosome movement 4 Cytokinesis Kinetochore Animal cells divide by constriction Tubulin subunits Motor protein Plant cells build a partition Kinetochore Cleavage furrow Microtubule Prophase: Chromosomes begin to condense. Spindle starts to form Prometaphase Nuclear envelope breaks down. Chromosomes attach to 2 spindle Telophase and Cytokinesis Cleavage furrow Centrosome at one spindle pole Prometaphase Centromere Chromosome, consisting of two sister chromatids genetically variable, haploid, cells – Stages of meiosis – Sexual life cycles Spindle Prophase Early mitotic spindle Chromosome 100 !m Vesicles forming cell plate 1 !m Contractile ring of microfilaments 5 6 1 How do the cytoplasmic organelles divide? The human life cycle Key • Mitochondria (and chloroplasts) are present in multiple copies, and randomly segregate into the two daughter cells. Ovary Mitosis Meiosis 1 Meiosis 2 MEIOSIS I: Separates homologous chromosomes METAPHASE I Diploid zygote (2n = 46) Testis Multicellular diploid adults (2n = 46) Figure 13.5 PROPHASE I FERTILIZATION MEIOSIS 7 INTERPHASE Ovum (n) Sperm Cell (n) Meiosis only occurs during gamete formation • Membrane bound organelles (e.g. ER) fragment along with the nuclear membrane and are reconstructed in the daughter cells Gametes are the only haploid cells Haploid gametes (n = 23) Haploid (n) Diploid (2n) ANAPHASE I MEIOSIS II: Separates sister chromatids TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Sister chromatids remain attached Sister chromatids Chiasmata Spindle Cleavage furrow Tetrad Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange Figure 13.8 segments; 2n = 6 in this example Homologous chromosomes separate Pairs of homologous Tertads line up chromosomes split up Haploid daughter cells forming chromosomes are still double Figure 13.8 Mitosis vs Meiosis Not paired Sister chromatids separate Some species reproduce asexually diploid • Produce genetically identical offspring by mitosis. • (basically just branching) Parent Bud Homologs pair in meiosis 1 haploid Sister chromatids separate in meiosis 2 0.5 mm Dandelion Hydra 2
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