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MITOSIS VS. MEIOSIS Body Cell Division MITOSIS AND MEIOSIS • Mitosis: -division of somatic (body) cells • Meiosis -division of gametes (sex cells) I. STEPS OF • • • • • MITOSIS Interphase Prophase Metaphase Anaphase Telophase (& cytokenesis) II. INTERPHASE • Cell goes through its regular functions • Visible nucleus, nuclear envelope and nucleolus III. PROPHASE • DNA inside the cell condenses and makes visible chromosomes • Nucleus begins to disappear • Spindle fibers begin to form IV. METAPHASE • Chromosomes line up along the center (equator) of the cell • This step is “quality control” and makes sure each chromosome divides equally V. ANAPHASE • Chromosomes split apart to become sister chromatids • Sister chromatids move to opposite sides of the cell VI. TELOPHASE • Chromosomes arrive at separate ends of the cell • Chromosomes relax and begin to uncoil • Nuclear membrane begins to reform • Spindle fibers disappear CYTOKINESIS • • Animal Cell Plant Cell The division of the cell cytoplasm that usually follows mitotic or meiotic division of the nucleus. General Definitions • Diploid – normal number of chromosomes in a body cell after mitosis (2n) o • Example: Humans have 46 chromosomes in each body cell Haploid – half the normal number of chromosomes after meiosis (n) o Example: Human sex cells (sperm and egg) have 23 chromosomes Meiosis Big Ideas • • • • Meiosis makes sex cells or gametes In meiosis, cell division happens twice and forms four cells with half the genetic material Meiosis reduces the number of chromosomes to half of the original number of chromosomes Meiosis provides genetic variation because all of the sex cells produced at the end have different genetic information Interphase • • • Cell goes through its regular functions DNA copies DNA is in the form of chromatin Prophase I • Chromatin (DNA) organizes to form visible chromosomes • Nuclear membrane breaks down • Spindle fibers start to form • Crossing over occurs Crossing Over (Prophase I) Crossing over – exchange of DNA from one homologous chromosome to another • It is responsible for genetic variation • After crossing over, no two sister chromatids are alike • Metaphase I • Homologous Chromosomes line up at the equator (middle) of the cell • Spindle fibers attach to the centromere of each chromosome Anaphase I • Homologous chromosomes move to the poles of the cell Telophase I • Cells divide for the first time • Cytokenesis separates the • • • • cytoplasm of each cell Two new cells are formed – they are NOT genetically identical Nuclear membrane reforms Chromosomes relax to form chromatin Spindle fibers disappear Prophase II • Chromatin (DNA) organizes to form visible chromosomes • Spindle fibers begin to form • Nuclear membrane breaks down Metaphase II • Chromosomes line up along the equator (middle) of the cell • Spindle fibers attach to the centromere of each chromosome Anaphase II • Sister chromatids are pulled apart • Chromosomes are pulled to the poles of each cell Telophase II • Cells divide • Cytokinesis fully • • • • separates the cytoplasm of each cell Nuclear membrane reforms Chromosomes relax Spindle fibers disappear Four genetically different sex cells (gametes) are Why do sex cells have HALF the chromosome number? Study Tools • P. 275 www.cellsalive.com • • Mitosis (body cell division) animation Meiosis (sex cell production) animation • Link: http://www.cellsalive.com/meiosis.htm