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MEIOSIS NOTES (11.4) (MEIOSIS NOTES 11.4) REPRODUCTION • Asexual- all of the parent DNA goes to offspring (miTosis-mainTains) • Sexual -used to create sex cells(mEiosis-rEduce) 2 TYPES OF CELLS BODY CELLS 2) SEX CELLS Chromosomes are: 1) autosomes 2) sex chromosomes 1) BODY CELLS -All cells other than sex cells -Also called somatic cells -Made by mitosis This scanning electron micrograph (courtesy of Dr. Marion J. Barnhart) shows the characteristic biconcave shape of red blood cells. BODY CELLS -Contain 2 copies of each chromosome -homologous chromosomes -have diploid #, 2n EX. Humans =46 SEX CELLS -Gametes -Eggs and sperm -Made by meiosis -Have haploid #, n -EX. Humans =23 HOW DO WE GET 46 CHROMOSOMES? Egg (haploid #) + Sperm(haploid #) ZYGOTE (diploid #) Ex. Humans 23 + 23 =46 MEIOSIS SEX CELLS mEiosis = rEduction division -starts with 1 diploid cell and ends up with 4 haploid cells **Meiosis I and Meiosis II MEIOSIS I CROSSING OVER Occurs during Prophase I of meiosis *synapsis Tetrads form and DNA is exchanged XX ADVANTAGE: genetic variation CROSSING OVER Adapted from: Morgan T.H., Sturtevant A.H., Muller H.J., and Bridges C.B., "The Mechansim of Mendelian Heredity", 1915. INDEPENDENT ASSORTMENT –ANAPHASE I MEIOSIS II Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Anaphase II The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells. MEIOSIS DIAGRAM EGG FORMATION (UNEQUAL CYTOKINESIS) AUTOSOMES VS. SEX CHROMOSOMES COMPARING MITOSIS AND MEIOSIS HOW MANY CELLS ARE MADE? Mitosis 2 Meiosis 4 COMPARING MITOSIS AND MEIOSIS ARE RESULTING CELLS GENETICALLY THE SAME OR DIFFERENT? MitosisGenetically the same Meiosis Genetically different COMPARING MITOSIS AND MEIOSIS WHAT TYPES OF CELLS RESULT IN THE PROCESS? (BODY CELLS OR GAMETES) Mitosis = Body cells Meiosis = Gametes COMPARING MITOSIS AND MEIOSIS WHAT ARE THE ADVANTAGES OF EACH PROCESS? MitosisGrowth and repair MeiosisFormation of sex cells and genetic variation