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 Meiosis 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

Meiosis Associated with Sex! Sexual Reproduction involves 2 parents Mixing of genetic information Life cycles, with MEIOSIS & FERTILIZATION

Life Cycles HAPLOID GAMETIC DIPLOID

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 2n1n VARIATION!

Meiosis I

Meiosis II Prophase II Metaphase II Anaphase II Telophase II Separation of sister chromatids 1n1n Results in 4 DIFFERENT cells.

Meiosis II

MEIOSIS -- Spermatogenesis

MEIOSIS -- Oogenesis Stimulated by Fertilization

MITOSIS vs MEIOSIS