Mitosis vs. Meiosis: A Comparative Guide to Cell Division

2/20/2018 - Double-stranded molecule made of nucleotides that stores genetic information (double helix) How does it store it? - as a long, continuous thread that consists of many genes    Chromatin: loosely compacted single strand Chromatid: tightly compacted, one of a pair Chromosome: two tightly compacted sister chromatids joined at the centromere Humans have 23 pairs of chromosomes:  Autosomes - chromosome pairs 1 through 22 - contain genes not directly related to the sex of an organism Ex. Eye and hair color  Sex Chromosome - the 23rd pair of chromosomes - control development of sex characteristics 1 2/20/2018  Gametes: sex cells - female (egg) - male (sperm)  Somatic Cells: body cells - make up tissue and organs Why do cells need to divide? *** DNA in gametes is passed on to offspring *** DNA is NOT passed on to offspring through cell division 1. Interphase - where DNA duplicate and form chromosomes 2. Mitosis - where the chromosomes divide and separate from each other 3. Cytokinesis - Cytoplasm divides into two daughter cells 1- growth 2- reproduction 3- repair     Occurs in 4 phases: PMAT 90% of the cell cycle is spent in interphase Chromosomes appear as loose coils called chromatin Three phases:  Gap 1, Synthesis and Gap 2  The cell grows and checks DNA to make sure code is undamaged then it duplicates the DNA and checks it again for any damaged code First stage of Mitosis - DNA long strands condense into short coils - Nuclear envelope breaks down - Centrioles begin to move to opposite poles - Spindle fibers form 2 2/20/2018      Chromosomes line up in the center of the cell Spindle fibers attach to the centromere of each chromosome 2 nuclear membranes begin to form around chromosomes (one for each new cell) Chromosomes begin to uncoil Spindle fibers fall apart  Spindle fibers shorten and pull sister chromatids apart, towards opposite poles  Divides cytoplasm into two cells and completes a full stage of the cell cycle Begins during Telophase  3 2/20/2018   Meiosis consists of two cell divisions without Interphase in the middle Occurs in gametes (sex cells) only   Mitosis is in my toes; Meiosis is in the ovaries OR Meiosis is what makes me unique (genetically unique as opposed to a genetic duplicate)  Egg and sperm each have 1 set of DNA - Sex cells are called haploid cells (n = 23 chromosomes)  When the sperm fertilizes the egg, the resulting zygote now has 2 sets of DNA - Somatic cells are called diploid cells (2n = 46 chromosomes)  When your skin cells replicate, you want them to create an exact copy (mitosis) When creating a new organism (reproduction), genetic variation increases survival of the species (meiosis). Fertilization: - egg and sperm come together and the cell now has a complete set of DNA (23 pairs, one from each parent) Cell makes a copy of DNA from Mom and from Dad. - Copies of each chromatid are made; they join at the centromere (cell must reduce chromosome number) - Homologous chromosomes pair up: one from each parent - Crossing over may occur 23 from egg duplicates to 46 23 from sperm duplicates to 46  Total chromosomes is 92      Nuclear membrane disappears Centrioles move to poles Spindle fibers form 4 2/20/2018   Chromosome pairs line up at equator of cell Spindle fibers attach to one of each chromosome pair  Chromosomes line up randomly on either side of the equator     Nuclear membranes form around two sets of DNA; spindle fibers detach Cytokinesis forms two unique cells, each with 23 pairs of chromosomes Paired chromosomes are pulled apart by spindle fibers  Each side will have some from Mom and some from Dad Second cell division  Prophase II  Metaphase II  Anaphase II  Telophase II  Cytokinesis that results in 4 genetically unique daughter cells egg + sperm = zygote haploid + haploid = diploid n + n = 2n 5 2/20/2018 Diploid or Haploid daughter cells # of Divisions Cell Type Number of daughter cells Daughter cells are:  Interphase     Mitosis      Gap 1 (G1) Synthesis (S) Gap 2 (G2) Prophase Metaphase Anaphase Telophase Mitosis Meiosis Diploid (2n=46) Haploid (n=23) 1 2 Somatic cells (body cells) Sex Cells (gametes) 2 4 Genetically identical Genetically unique INTERPHASE HAS THREE PHASES  Interphase    Gap 1 (G1) Synthesis (S) Gap 2 (G2) Cytokinesis 6 2/20/2018  Interphase  Gap 1 (G1)    During G1 the cell grows, caries out normal functions, and replicates its organelles. There is also a CRTICAL CHECKPOINT. The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged.  Interphase    Gap 1 (G1) Synthesis (S) Gap 2 (G2) Interphase During Synthesis (S phase) DNA is synthesized (made) that is: copied, replicated, duplicated.   Interphase Mitosis    During G2 the cell undergoes additional growth. There is also a CRITICAL CHECKPOINT. The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged. Gap 1 (G1) Synthesis (S)   Prophase Metaphase Anaphase Telophase Cytokinesis Cytoplasm divides, the cell divides. 7