Meiosis Chapter 11 Sec. 4 Meiosis Reduces # of chromosomes to half Diploid (2n) to haploid (1n) Meiosis Produces gametes = sperm and egg Each contains 23 chromosomes Stages of Meiosis Goes through G1, S, G2 Basically go through mitosis twice 1 cell divides into 4 cells with half of information Meiosis I Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 and cytokinesis 1 Prophase 1 DNA coils into chromosomes Spindle fibers appear Nuclear envelope disappears Prophase 1 Homologous pairs form tetrads Crossing over can occur here Exchange of genetic material between chromosomes Prophase 1 Crossing over results in genetic recombination Produces new genes Metaphase 1 Tetrads line up along the equator of cell Kinetochore attach to centromeres Anaphase 1 Kinetochore pulls tetrads apart to separate poles Randomly separates= independent assortment Provides variation Telophase 1 Chromosomes reach separate ends Cytokinesis begins Meiosis 1 Original cell produces two new cells Each contains one chromosome= haploid Meiosis 2 Second stage of meiosis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 and Cytokinesis Prophase 2 Spindle fibers form Nuclear envelope disappears Metaphase 2 Chromosomes move to middle of cell Anaphase 2 The chromatids separate and move towards opposite poles Telophase 2 Nuclear membrane forms Cytokinesis occurs Results in 4 new cells each with haploid # meiosis Gametes In animals meiosis = gametes Occurs in testes and ovaries Only in sex chromosomes Spermatogenesis Production of sperm cells Oogenesis Production of eggs Asexual Reproduction Production of offspring from one parent Mitosis, binary fission or budding Genetically identical Sexual Reproduction Production of offspring through meiosis and union of sperm and egg Genetically different from parents