MEKANISME SEL DAN SIKLUS HIDUP TANAMANMITOSIS Istilah mitosis : proses yg menghasilkan dua sel anak yg identik. Mitosis memegang peranan dalam pertumbuhan dan perkembangan organisme. Pada tanaman mitosis terjadi pd sel-sel meristematis, misalnya ujung-ujung akar, dan ujung batang, kambium. Mitosis Prophase • • • • • In prophase, the cell begins the process of division. 1. The chromosomes condense. The proteins attached to the DNA cause the chromosomes to go from long thin structures to short fat one, which makes them easier to pull apart. 2. The nuclear envelope disappears. The double membrane that surround the nucleus dissolves into a collection of small vesicles, freeing the chromosomes to use the whole cell for division 3. The centrosomes move to opposite poles. During interphase, the pair of centrosomes were together just outside the nucleus. In prophase they separate and move to opposite ends of the cell. 4. The spindle starts to form, growing out of the centrosomes towards the chromosomes. Metaphase • Metaphase is a short resting period where the chromosomes are lined up on the equator of the cell, with the centrosomes at opposite ends and the spindle fibers attached to the centromeres. Everything is aligned for the rest of the division process to occur. the centromeres divide. and the chromosomes are pulled to opposite poles. each individual chromosome goes from: – 1 chromosome with 2 chromatids – to: – 2 chromosomes with one chromatid each. . At this point. towards the centrosomes. • Then the spindle fibers contract.Anaphase • In anaphase. • The cytoplasm is divided into 2 separate cells. • The chromosomes are at the poles of the spindle.Telophase • In telophase the cell actually divides. . the process of cytokinesis. • The spindle disintegrates • The nuclear envelope reforms around the two sets of chromosomes. Plant and animal cells divide the cytoplasm in different ways. Cell membranes form along the surfaces of this wall. In plant cells. • . the 2 cells have become separate. When the new wall joins with the existing side wall. a ring of actin fibers (microfilaments are composed of actin) forms around the cell equator and contacts.Cytokinesis • • • The organelles (other than the chromosomes) get divided up into the 2 daughter cells passively: they go with whichever cell they find themselves in. a new cell wall made of cellulose forms between the 2 new nuclei. about where the chromosomes lined up in metaphase. pinching the cell in half. In animal cells. Meiosis • Reduces the number of chromosomes in new cells to half the number in the original cell • Produces gametes (sperm and egg cells) . Terjadi 4 kejadian penting pada meiosis • Perpasangan kromosom yg homolog (synapsis) • Pertukaran bagian kromosom (crossing over) • Distribusi kembali kromosom • Susunan materi genetik mungkin berbeda dg tetua akibat crossing over . eggs) • Arise from germ cells ovaries testes anther ovary .Gamete Formation • Gametes are sex cells (sperm. Stages of Meiosis Meiosis I • Prophase I Meiosis II • Prophase II • Metaphase I • Anaphase I • Telophase I • Metaphase II • Anaphase II • Telophase II . DNA Replication . Meiosis . Meiosis . . Meiosis I Each homologue in the cell pairs with its partner. then the partners separate . Stages Prophase I Metaphase I Anaphase I Telophase I .Meiosis I . condensed chromosome pairs with its homologue (synapsis) • Homologues swap segments (crossing over) .Prophase I • Each duplicated. Homologous Chromosomes . Homologous Chromosomes . Synapsis . Crossing Over . each chromosome contains both maternal and parental segments • Creates new allele combinations in offspring .Effect of Crossing Over • After crossing over. . . Metaphase I • Chromosomes are pushed and pulled into the middle of cell • Sister chromatids of one homologue orient toward one pole. and those of other homologue toward opposite pole . . . Anaphase I • Homologous chromosomes segregate from each other randomly (independent assortment) • Independent assortment results in genetic variation . Independent Assortment . Telophase I and Cytokinesis • The chromosomes arrive at opposite poles • The cytoplasm divides • There are now two haploid cells • This completes Meiosis I . Meiosis II • The two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated) . Stages Prophase II Metaphase II Anaphase II Telophase II .Meiosis II . Prophase II • Microtubules attach to the kinetochores of the duplicated chromosomes • Chromosomes move toward the spindle’s equator . midway between the poles .Metaphase II • All of the duplicated chromosomes are lined up at the spindle equator. Anaphase II • Sister chromatids separate to become independent chromosomes and move to opposite poles . Telophase II and Cytokinesis • The chromosomes arrive at opposite ends of the cell • A nuclear envelope forms around each set of chromosomes • The cytoplasm divides • There are now four haploid cells Meiosis Animation I Meiosis Animation II . Results of Mitosis and Meiosis • Mitosis – Two diploid cells produced – Each identical to parent • Meiosis – Four haploid cells produced – Differ from parent and one another * Buatlah Uraian tentang Mitosis dan Miosis . SIKLUS HIDUP TANAMAN . . J. Tassel Microsporocyte Megasporocyte (2n) Meiosis Microspore (n) Germinated pollen grain Sperm nuclei (n) Fertilization Ear shoot Mature spotophyte (2n) Endosperm (3n) Embryo (2n) Mature kernel (2n) 4 megaspores (n) Degenerating megaspores Surviving megaspores Mature embryo sac Polar nuclei (n) . B. H. D. L. F. I.MAIZE LIFE CYCLE A. Q. E. N. R. C. O. G. P. M. K. Gametogenesis Tumbuhan • Mikrosporogenesis (pada anther) • Megasporogenesis (pada bunga betina/ovarium) . Canna Hibiscus . Microsporogenesis . Megasporogenesis . Megasporogenesis & Megagametogenesis . . Megasporogenesis & Megagametogenesis . Megasporogenesis & Megagametogenesis .
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