9th Grade Cellular reproduction

Chromosomes are condensed DNA.

  • The Centromere is part of chromosome where sister chromatids are held together.
  • 1chromosome = 2 chromatids 

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MITOSIS (ASEXUAL REPRODUCTION)

  • Mitosis’s function is to grow and repair/maintain body.   * A cell grows, and divides, and repeats during its life.
  • 1parentcell(46chromosomes)produces2<strong>identical</strong>daughtercells(46chromosomeseach).1 parent cell (46 chromosomes) produces 2 <strong>identical</strong> daughter cells (46 chromosomes each). 
  • Your cells do not divide (perform mitosis) continually. Most of the time, they are in interphase.
  • Cancer is when cells uncontrollably divide. 

\ INTERPHASE (PRE MITOSIS)

  • The cell grows in size and performs regular functions.
  • Chromosomes are replicated (doubled).

\ FOUR STAGES OF MITOSIS

  • PMAT : Prophase, Metaphase, Anaphase, Telophase
  • Prophase    * Centrioles (poles) appear and move to opposite ends of cell.   * Spindle fibers form between the poles.
  • Metaphase   * Chromatids line up in the middle of the cell and attach to the spindle fibers.
  • Anaphase   * Chromatids separate and begin to move to opposite ends of of the cell.
  • Telophase   * Two new nuclei form and the chromosomes appear as chromatin (threads rather than rods).   * Mitosis ends.

\ Cytokinesis 

  • Cell membrane moves inward to create two daughter cells (each with its own nucleus and identical chromosomes). 

\ \ MEIOSIS (SEXUAL REPRODUCTION) 

  • Prophase 1   * Chromosomes line up with their homologous pairs.      * Homologous chromosomes are 2 chromosomes that are about the same size & have the same gene type in the same place.   * Crossing over occurs (homologous pairs transfer their genetic info, creating recombinant chromosomes).
  • Metaphase 1    * Chromosomes line up in the middle of the cell in pairs and attach to spindle fibers.
  • Anaphase 1   * The spindle fibers pull the homologous chromosomes apart and they move to opposite ends of the cell.
  • Telophase 1 and Cytokinesis (ends meiosis one)   * The nuclear membranes reform around the chromosomes, the two cells are separate.
  • Prophase 2   * The two haploid cells start to go through meiosis 2.   * The cells nuclear membrane breaks back down, and spindle fibers begin to form. 
  • Metaphase 2   * Chromosomes line up in the middle of the cell and attach to spindle fibers (single file).
  • Anaphase 2    * Sister chromatids separate and are pulled to opposite sides of the cell by spindle fibers.
  • Telophase 2 and Cytokinesis   * The nuclear membranes reforms.   * Four new haploid cells (23 chromosomes) have formed!   * These cells are gametes, and each one is unique and different from each other (NO identical cells, unlike cells from mitosis). 
  • Nondisjunction occurs when chromosomes don't separate correctly.   * A cell may receive too many or too little chromosomes in the separation. 

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