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Cell Division Making New Cells Cell Division • Cells come from pre-existing cells… • Cells need to reproduce! – Single-celled organisms -- asexual reproduction. – Multi-celled organisms – growth. • Cell Division = Cytokinesis • Nuclear Division = Karyokinesis Prokaryotes – Binary Fission • Simple Eukaryotes – more complex • Chromosomes • Chromosome Structure – Chromatin – Unduplicated – Duplicated • Chromosome Number – Diploid • Somatic cells (body cells) – Haploid • Germ cells (sex cells) Karyokinesis • Mitosis – Somatic cells (body cells) – “Cloning” of genetic information – exact copies made and distributed to new cells. – Chromosome # is retained (stays the same). • Meiosis – Germ cells (sex cells) – Genetic information is shuffled – new cells are each different. – Chromosome # is cut in half. Cell Cycle Chromosome Duplication • During S-phase = “Synthesis” • Why?.... • So that later, the sister chromatids can separate into different (new) cells! Mitosis • • • • Prophase Metaphase Anaphase Telophase Prophase •Nuclear Envelope Disappears •Nucleolus Disappears •Chromosomes Condense •Chromatin Chromosomes •Spindle Fibers (Microtubules) •Attach to Centromeres •Attach to M.T.O.C.s Metaphase •Chromosomes line up on the ‘Metaphase Plate’ •pushed & pulled by the spindle fibers •Spindle Apparatus well developed. Anaphase •Chromosomes each broken at their centromeres •spindle fibers on each side shorten •New (unduplicated) chromosomes move toward the M.T.O.C.s Telophase •Chromosomes stop moving when they reach the spindle poles (at the M.T.O.C.s) •Nuclear Envelope re-forms (2x) •Nucleolus re-forms (2x) •Spindle fibers disappear •Cytokinesis Cytokinesis Cleavage Furrow divides the cells Cell Plate divides the cells Meiosis • Associated with Sex! • Sexual Reproduction involves – 2 parents – Mixing of genetic information – Life cycles, with MEIOSIS & FERTILIZATION Life Cycles HAPLOID DIPLOID GAMETIC Meiosis • Mixing of Genetic Information • Germ Cells (Sex Cells) • Reduction in Chromosome Number – Diploid Haploid • 2 Divisions – Meiosis I --- P,M,A,T – Meiosis II --- P,M,A,T • Results in 4 cells Meiosis I • • • • Prophase I Metaphase I Anaphase I Telophase I • Pairing and separation of Homologous Chromosomes • Crossing Over • Independent Assortment • 2n1n VARIATION! Meiosis I Meiosis II • • • • Prophase II Metaphase II Anaphase II Telophase II • Separation of sister chromatids • 1n1n • Results in 4 DIFFERENT cells. Meiosis II MEIOSIS -- Spermatogenesis MEIOSIS -- Oogenesis Stimulated by Fertilization MITOSIS vs MEIOSIS
